ip advanced.pdf
TRANSCRIPT
-
8/22/2019 IP advanced.pdf
1/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 1
Alcatel University - 8AS 90200 1140 VT ZZA Ed.011
Routing
-
8/22/2019 IP advanced.pdf
2/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 2
2
Page intentionally left blankPage intentionally left blank
-
8/22/2019 IP advanced.pdf
3/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 3
3
1 TitleSession presentation
Objective: to be able to configure RIP and OSPF dynamic
routing
program:
1 Overview
2 RIP protocol
3 OSPF protocol
-
8/22/2019 IP advanced.pdf
4/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 4
4
Page intentionally left blank
-
8/22/2019 IP advanced.pdf
5/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 5
Alcatel University - 8AS 90200 1140 VT ZZA Ed.015
Routing
1. Overview
-
8/22/2019 IP advanced.pdf
6/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 6
6
Page intentionally left blank
-
8/22/2019 IP advanced.pdf
7/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 7
7
1- OverviewVarious types of routing
Static
Prevent traffic due to routing protocol
Easy design on small network
Risk of errors
Programmed manually
No re-routing in case of failure
Dynamic
Re-route automatically the traffic in case of network failure
Ideal for large network
Involve over processing in the routers
Generate over traffic on the network
Static routing
Static routing is manually performed by the network administrator. The administrator is responsible for discoveringand propagating routes through the network. These definitions are manually programmed in every routing devicein the environment.
Once a device has been configured, it simply forwards packets out the predetermined ports. There is nocommunication between routers regarding the current topology of the network.
In small networks with minimal redundancy, this process is relatively simple to administer. However, there areseveral disadvantages to this approach for maintaining IP routing tables:
Static routes require a considerable amount of coordination and maintenance in non-trivial networkenvironments.
Static routes cannot dynamically adapt to the current operational state of the network. If a destinationsubnetwork becomes unreachable, the static routes pointing to that network remain in the routing table. Trafficcontinues to be forwarded toward that destination. Unless the network administrator updates the static routes toreflect the new topology, traffic is unable to use any alternate paths that may exist.
Dynamic routing:
Dynamic routing algorithms allow routers to automatically discover and maintain awareness of the paths throughthe network.
-
8/22/2019 IP advanced.pdf
8/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 8
8
1- OverviewPrinciple of routing tables :
Fill-in this table
Network Mask Next hop If
Network Mask Next hop If
204.92.77.0 255.255.255.0
192.168.201.0 255.255.255.0
204.92.76.0 255.255.255.0 e0
e1
204.92.76.2
204.92.75.0 255.255.255.0 e2
204.92.75204.92.75.0.0
192.168.201192.168.201.0.0204.92.76204.92.76.0.0204.92.77204.92.77.0.0R1
R2R2
.1.1 .1.1.1.1.2.2
0.0.0.0(default) 0.0.0.0
192.168.201.0 255.255.255.0
204.92.76.0 255.255.255.0 e1e1
204.92.76.1
e0
.2.2
e0e0e1e1
e2
e1e1
e0
Fill-in this table
Network Mask Next hop If
An important function of the IP layer is IP routing. This provides the basic mechanism for routers to interconnectdifferent physical networks.
The router only has information about various kinds of destinations:
networks that are directly attached to one of the physical networks to which the router is attached.
Hosts or networks for which the router has been given explicit definitions.
The metrics provide indication about cost of a route to a destination.
Metrics are based on :
the number of hops,
the bandwidth,
the delay, ...
-
8/22/2019 IP advanced.pdf
9/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 9
9
1- OverviewRouting table : the metric
R1
R2
192.168.201.0
204.92.76.0
204.92.77.0
.1 .1.1.2
204.92.75.0
.2
.2
Network Mask Next hop metric
204.92.77.0 255.255.255.0192.168.201.0 255.255.255.0204.92.76.0 255.255.255.0
204.92.76.1
204.92.75.0 255.255.255.0 204.92.76.1 e1
204.92.77.0 255.255.255.0 e2
001
1
0
Secondary route
Primary routePrimary route
204.92.75.0 255.255.255.0 204.92.77.1 e2 1
If
e1e1e0
e1e1
e0e0e1e1
e2
e2
The metrics provide indication about cost of a route to a destination and allow the choice when several routes areavailable.
-
8/22/2019 IP advanced.pdf
10/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 10
10
ISDN
1- OverviewOther advantage of static routing
If dynamic routing on ISDN linkIf dynamic routing on ISDN link
The connection should beThe connection should be continiouselycontiniousely onon
for routing information updatefor routing information updateHigh costHigh cost
Normally, static routes are used only in simple network topologies. However, there are additional circumstanceswhen static routing can be attractive. For example, static routes can be used:
To manually define a default route. This route is used to forward traffic when the routing table does not contain amore specific route to the destination.
To define a route that is not automatically advertised within a network.
When utilization or line tariffs make it undesirable to send routing advertisement traffic through lower-capacityWAN connections.
When complex routing policies are required. For example, static routes can be used to guarantee that trafficdestined for a specific host traverses a designated network path.
To provide a more secure network environment. The administrator is aware of all subnetworks defined in theenvironment. The administrator specifically authorizes all communication permitted between these subnetworks.
To provide more efficient resource utilization. This method of routing table management requires no networkbandwidth to advertise routes between neighboring devices. It also uses less processor memory and CPU cyclesto calculate network paths.
-
8/22/2019 IP advanced.pdf
11/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 11
11
network
140.252.13.32
1- OverviewExample of routing (1)
140.252.1.92 140.252.1.32 140.252.1.11
140.252.1.4
Internet
140.252.1.183
140.252.1.29
140.252.13.33 140.252.13. 34140. 252.13.35
140.252.13.66
140.252.13.65
network
140.252.1
140 252. .13 35.IP @ :
1 0 0 0 1 1 1 0 1 1 1 1 1 1 0 0 0 0 1 0 0 0 1 10 0 0 0 1 1 0 1
140 252. .13 32.Network :
1 0 0 0 1 1 1 0 1 1 1 1 1 1 0 0 0 0 1 0 0 0 0 00 0 0 0 1 1 0 1
1 1 1 1 1 1 1 11 1 1 1 1 1 1 11 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0
Masque :
/27
-
8/22/2019 IP advanced.pdf
12/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 12
12
Destination Gateway Flags InterfaceRefcnt Use
1- OverviewExample of routing (2)- Routing table
140.252.1.92 140.252.1.32 140.252.1.11
140.252.1.4
Internet
140.252.1.183
140.252.1.29
140.252.13.33 140.252.13. 34140. 252.13.35
140.252.13.66
140.252.13.65Network
140.252.13.32
Network
140.252.1
140.252.13.65/32
To go to :
UU
U: This routeU: This route isis UpUp
Refcnt: nb of TCP session
Use : nb of packets sent on this @
0 0 eth0
ethernet
140.252.13.35
G: Go througth Gateway
G
H: This address is a full IP@ of host
H
-
8/22/2019 IP advanced.pdf
13/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 13
13
Network
140.252.13.32
1- OverviewExample of routing (3)- Routing table
140.252.1.92 140.252.1.32 140.252.1.11
140.252.1.4
Internet
140.252.1.183
140.252.1.29
140.252.13.33140.252.13.35
140.252.13.66
140.252.13.65
Network
140.252.1
Direct route : route connected to this machine , on this interface
140.252.13.34
Destination Gateway Flags InterfaceRefcnt Use
140.252.13.65/32 140.252.13.35 U G H eth00 0
To go to :
140.252.13.32/27
U: This routeThis route isis UpUp
U 4 2543
_: This address is an IP@ of network
_
_: direct route
140.252.13.34 _ eth0
ethernet
-
8/22/2019 IP advanced.pdf
14/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 14
14
1- OverviewExample of routing (4)- Routing table
140.252.1.92 140.252.1.32 140.252.1.11
140.252.1.4
Internet
140.252.1.183
140.252.1.29
140.252.13.33140.252.13.35
140.252.13.66
140.252.13.65
Network
140.252.13.32
Network
140.252.1
Destination Gateway Flags
140.252.13.65/32 140.252.13.35 U G H
140.252.13.32/27 140.252.13.34 U _ _
Loopback between 2 applications
Interface
eth0
Refcnt Use
0 0
140.252.13.34
eth04 2543
To go to :
127.0.0.1 /32
U:U: thisthis routeroute isis UpUp
UU 0 0 lo0
loopback
_: direct route
127.0.0.1 _
H: This address is a full IP@ of host
H
-
8/22/2019 IP advanced.pdf
15/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 15
15
1- OverviewExample of routing (5)- Routing table
140.252.1.92 140.252.1.32 140.252.1.11
140.252.1.4
Internet
140.252.1.183
140.252.1.29
140.252.13.33140.252.13.35
140.252.13.66
140.252.13.65
Network
140.252.13.32
Network
140.252.1
Destination Gateway Flags
140.252.13.65 /32 140.252.13.35 U G H
140.252.13.32 /27 140.252.13.34U _ _
InterfaceRefcnt Use
0 0
140.252.13.34
eth04 2543
127.0.0.1 /32U _ H
lo00 0127.0.0.1default
Default route
U
U: This routeU: This route isis UpUp
eth0
140.252.13.33
Go through
G: indirect route
G_ 0 0 eth0
ethernet
-
8/22/2019 IP advanced.pdf
16/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 16
16
1- OverviewExample of routing (6)- routing table using
140.252.1.92 140.252.1.32 140.252.1.11140.252.1.4
Internet
140.252.1.183
140.252.1.29
140.252.13.33140.252.13.35
140.252.13.66
140.252.13.65
Network
140.252.13.32
Network
140.252.1
140.252.13.34
Destination Gateway Flags
140.252.13.65 /32 140.252.13.35 U G H
140.252.13.32 /27 140.252.13.34 U _ _
Interface
eth0
Refcnt Use
0 0
eth04 2543
default 140.252.13.33 eth00 0U G _
127.0.0.1 /32 U _ H lo00 0127.0.0.1
Example :Search IP@ 140.252.13.35
1- Search of precise IP @ (among entries with flag=H)=> fail
2- Search on network@, The network@ 140.252.13.32 is found=> send the packet to the MAC@ of the search host (140.252.13.35) on Ethernet interface : eth0
-
8/22/2019 IP advanced.pdf
17/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 17
17
1- OverviewExample of routing (7)- routing table using
140.252.1.92 140.252.1.32 140.252.1.11 140.252.1.4
Internet
140.252.1.183
140.252.1.29
140.252.13.33140.252.13.35
140.252.13.66
140.252.13.65Network
140.252.13.32
Network
140.252.1
140.252.13.34
Destination Gateway Flags
140.252.13.65 /32 140.252.13.35 U G H
140.252.13.32 /27 140.252.13.34 U _ _
Interface
eth0
Refcnt Use
0 0
eth04 2543
default 140.252.13.33 eth00 0U G _
127.0.0.1 /32 U _ H lo00 0127.0.0.1
Example :search IP @ 140.252.13.65
1- Search of precise IP @ (among entries with flag=H)=>the @ 140.252.13.65 is found
=> indirect route (G), sends the packet to MAC@ of the router (140.252.13.35) on Ethernet interface : eth0
-
8/22/2019 IP advanced.pdf
18/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 18
18
1- OverviewExample of routing (8)- routing table using
140.252.1.92 140.252.1.32 140.252.1.11140.252.1.4
Internet
140.252.1.183
140.252.1.29
140.252.13.33140.252.13.35
140.252.13.66
140.252.13.65
Network
140.252.13.32
Network
140.252.1
140.252.13.34
Destination Gateway Flags
140.252.13.65 /32 140.252.13.35 U G H
140.252.13.32 /27 140.252.13.34 U _ _
Interface
eth0
Refcnt Use
0 0
eth04 2543
default 140.252.13.33 eth00 0U G _
127.0.0.1 /32 U _ H lo00 0127.0.0.1
1- Search of precise IP @ (among entries with flag=H)=> fail
3- Selection of dfault => indirect route (G), sends the packet to MAC@ of the router (140.252.13.33)on Ethernet interface : eth0
Exemple :recherche @IP 192.207.117.2
2- Search on network@, => fail
-
8/22/2019 IP advanced.pdf
19/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 19
19
1- OverviewExample of routing (9)- Configuration
% netstat -rnDestination Gateway Flags InterfaceRefcnt Use
140.252.1.92 140.252.1.32 140.252.1.11
140.252.1.4
Internet
140.252.1.183
140.252.1.29
140.252.13.33140.252.13.35
140.252.13.66
140.252.13.65
Network
140.252.13.32
Network
140.252.1
140.252.13.34
Creation of direct routes : at the (ifconfig) : route creation : command route .Examples:
default 140.252.13.33 eth00 0U G _
route add default 140.252.13.33
140.252.13.65 /32 140.252.13.35 U G H 0 0 eth0
route add -host 140.252.13.65 140.252.13.35
127.0.0.1 /32U _ H
lo00 0127.0.0.1
One entry for loopback
140.252.13.32 /27 140.252.13.34 U _ _ eth00 0
One entry for the local network
-
8/22/2019 IP advanced.pdf
20/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 20
20
1- OverviewExample of routing (12)
140.252.1.92 140.252.1.32 140.252.1.11
140.252.1.4
Internet
140.252.1.183
140.252.1.29
140.252.13.33 140.252.13.34140.252.13.35
140.252.13.66
140.252.13.65
Network
140.252.13.32
Network
140.252.1
Destination Gateway Flags InterfaceRefcnt Use
0 0
H: This address is a full IP@ of host
H140.252.13.65 /32
To go to :
UU
U: This routeU: This route isis UpUp
eth0
ethernet
140.252.13.35
G: go through Gateway
G
-
8/22/2019 IP advanced.pdf
21/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 21
21
1- OverviewExample of routing (13)
140.252. 1.92 140.252.1.32 140.252.1.11
140.252.1.4
Internet
140.252.1.183
140.252.1.29
140.252.13.33140.252.13.35
140.252.13.66
140.252.13.65
network
140.252.13.32
network
140.252.1
140.252.13.34
Direct route : route connected to this machine , on this interface
Destination Gateway Flags
140.252.13.65 /32 140.252.13.35 U G H
Interface
eth0
Refcnt Use
0 0
eth0
ethernet
_: H: This address is a network IP @
_
To go to :
140.252.13.32 /27
_: direct route
140.252.13.33 _
U: This route is Up
U 0 0
-
8/22/2019 IP advanced.pdf
22/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 22
22
1- OverviewExample of routing (14)
140.252. 1.92 140.252.1.32 140.252.1.11
140.252.1.4
Internet
140.252.1.183
140.252.1.29
140.252.13.33140.252.13.35
140.252.13.66
140.252.13.65
Network
140.252.13.32
Network
140.252.1
140.252.13.34
Destination Gateway Flags
140.252.13.65 /32 140.252.13.35 U G H
Interface
eth0
Refcnt Use
0 0
eth0_140.252.13.32 /27 140.252.13.33 _U 0 0
Loopback between 2 applications
127.0.0.1 /32 UU 0 0 lo0
loopback
127.0.0.1_ H
-
8/22/2019 IP advanced.pdf
23/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 23
23
1- OverviewExample of routing (15)
140.252. 1.92 140.252.1.32 140.252.1.11
140.252.1.4
Internet
140.252.1.183
140.252.1.29
140.252.13.33140.252.13.35
140.252.13.66
140.252.13.65
Network
140.252.13.32
Network
140.252.1
140.252.13.34
Destination Gateway Flags
140.252.13.65 /32 140.252.13.35 U G H
Interface
eth0
Refcnt Use
0 0
eth0_140.252.13.32 /27 140.252.13.33 _
U
0 0
127.0.0.1 /32
UU
0 0 lo0127.0.0.1 _ H
140.252.1.29
G: go through Gateway
G s0
SerialInterface
To go to :
default
U: This routeU: This route isis UpUp
UU 0 0_
-
8/22/2019 IP advanced.pdf
24/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 24
24
Cisco- Static route command
ipip routeroute netnet--idid netmasknetmask {nextnext--hophop--ipip@@ | interface} [distancedistance]
ipip routeroute 172.31.10.0172.31.10.0 255.255.255.0255.255.255.0 10.10.10.210.10.10.2 101101
Examples :
ipip routeroute 0.0.0.00.0.0.0 0.0.0.00.0.0.0 Serial3Serial3 192.168.20.1192.168.20.1
2- Get out by this interface
3- pass by this gateway1- To go to this destination
4- The cost to reach the destination is
ipip routeroute 0.0.0.00.0.0.0 0.0.0.00.0.0.0 Ethernet0Ethernet0broadcast interface : the route will be insertedinto the routing table only when the broadcast
interface is up
If you point a static route to a broadcast interface,
for example, ip route 0.0.0.0 0.0.0.0 Ethernet0
the route will be inserted into the routing table only when the broadcast interface is up.
This configuration is not recommended because when the next hop of a static route points to an interface, the router considerseach of the hosts within the range of the route to be directly connected through that interface.
With this type of configuration, a router will perform Address Resolution Protocol (ARP) on the Ethernet for every destination therouter finds through the default route because the router will consider all of these destinations as directly connected to Ethernet0.
Specifying a numerical next hop on a directly connected interface will prevent the router from performing ARP or eachdestination address.
However, if the interface with the next hop goes down and the numerical next hop is reachable through a recursive route, youshould specify both the next hop IP address and the interface through which the next hop should be found.
For example, ip route 0.0.0.0 0.0.0.0 Serial3 192.168.20.1
Administrative distance is the feature used by routers to select the best path when there are two or more different routes tothe same destination from two different routing protocols. Administrative distance defines the reliability of a routing protocol.
Each routing protocol is prioritized in order of most to least reliable (believable) using an administrative distance value. Thesmaller the administrative distance value, the more reliable the protocol.
-
8/22/2019 IP advanced.pdf
25/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 25
25
172.31.10.0172.31.10.0
/24/24
E0
.2.2
.1.1
192.168.20.0 /30192.168.20.0 /30
.11
S3.22
S1
10.10.10.0 /3010.10.10.0 /30
.11
S2
.22S0
192.168.10.0 /30192.168.10.0 /30
.22
S0.11S0
Cisco - Static routing configuration example
Internet R1R1 R2R2
64kb/s
2Mb/s2Mb/s
R2#show ip route
Codes: C - connected, S - static, * - candidate default
Gateway of last resort is 10.10.10.1 to network 0.0.0.0
C 172.31.10.0172.31.10.0/24 is directly connected, Ethernet0
C 192.168.20.0192.168.20.0/30 is directly connected, Serial1
C 10.10.10.010.10.10.0/30 is directly connected, Serial0
ip route 0.0.0.0 0.0.0.0 Serial0 10.10.10.110.10.10.1default route
Other administrative distance
ip route 0.0.0.0 0.0.0.0 Serial1 192.168.20.1192.168.20.1 250250
Defaultadministrativedistance = 1
S* 0.0.0.0/0 [1/0] via 10.10.10.110.10.10.1
Only the primary route is inserted
R1#show ip route
Codes: C - connected, S - static, * - candidate default
Gateway of last resort is 0.0.0.0 to network 0.0.0.0
C 10.10.10.010.10.10.0/30 is directly connected, Serial2
C 192.168.10.0192.168.10.0/30is directly connected, Serial0
C 192.168.20.0192.168.20.0/30is directly connected, Serial3
ip route 0.0.0.0 0.0.0.0 Serial3/0
ip route 172.31.10.0172.31.10.0 255.255.255.0 Serial3 192.168.20.2192.168.20.2 250250
ip route 172.31.10.0172.31.10.0 255.255.255.0 Serial2 10.10.10.210.10.10.2
primary
S* 0.0.0.0/0 is directly connected, Serial3/0
S 172.31.10.0172.31.10.0/24 [250/0] via 10.10.10.210.10.10.2, Serial2
By default, static routes have an administrative distance of one, which gives them precedence over routes fromdynamic routing protocols. By increasing the administrative distance to a value greater than that of a dynamicrouting protocol, the static route can be a safety net in the event that dynamic routing fai ls.
If you would specify an administrative distance for a static route.This kind of static route is called "floating" static.It is installed in the routing table only when the preferred route disappears.
-
8/22/2019 IP advanced.pdf
26/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 26
26
1- OverviewExercise : Static routing
Internet
172.16.0.0
/16
10.2.0.0/16
10.1.0.0/16
192.168.2.0
/24
192.168.1.0
/24
172.17.0.0/16
IP@:1
IP@:2
IP@:3
IP@:4
IP@:5
IP@:6
IP@:7
IP@:8
IP@:9
IP@:10
10.1.0.0/16@IP1
10.2.0.0/16@IP2
Routing Table
172.16.0.0/16@IP4
10.2.0.0/16@IP3
Routing Table
172.17.0.0/16@IP5
172.16.0.0/16@IP9
Routing Table
192.168.1.0/24@IP7
172.17.0.0/16@IP6
Routing Table
192.168.2.0/24@IP8
0.0.0.0 / 00.0.0.0 / 0 @IP3@IP3
0.0.0.0 / 00.0.0.0 / 0 @IP5@IP5
192.168.0.0/16192.168.0.0/16 @IP6@IP6
10.1.0.0/1610.1.0.0/16 @IP2@IP2
0.0.0.0 / 00.0.0.0 / 0 @IP10@IP10
10.0.0.0 / 810.0.0.0 / 8 @IP4@IP4
192.168.0.0/16192.168.0.0/16 @IP4@IP4
172.17.0.0/16172.17.0.0/16 @IP4@IP4
0.0.0.0 / 00.0.0.0 / 0 @IP9@IP9
Complete the routing tables of the various routers to get access to all destinations.
-
8/22/2019 IP advanced.pdf
27/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 27
27
1- OverviewDynamic routing principle
Routers advertise the networks
they can reach
Routers calculate the routes from
advertisementsadvertisements
-
8/22/2019 IP advanced.pdf
28/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 28
28
1- OverviewVarious routing protocols algorithms
Algorithm of routing
Distance VectorDistance Vector Link StateLink State
RIP
BGP
IGRP (CISCO)DECnet (Phase IV)
OSPF
IS-IS
DECnet (Phase V)
RIP : Routing Information Protocol
IS-IS : Intermediate System to Intermediate System
OSPF : Open Shortest Path First
IGRP: Internet Gateway Routing Protocol
BGP: Border Gateway Protocol
The automatic discovery of routes can use a number of currently available dynamic routing protocols. Thedifference between these protocols is the way they discover and calculate new routes to destination networks.They can be classified into three broad categories:
- Distance vector protocols
- Link state protocols
-
8/22/2019 IP advanced.pdf
29/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 29
29
1- OverviewDistance vector : principle
NetworkNetwork11 NetworkNetwork
55
NetworkNetwork44R1R1
R2R2 R3R3
R4R4
NetworkNetwork22
NetworkNetwork33
Network 2Network 2
Network
2
Network
2(1hop,R
3)
Network 3Network 3Network 3Network 3 (1 hop, R4)
Network 4Network 4
Network4Network4(0hop,e0)
Network 5Network 5
Network5
Network5(0hop,e2)
Routers based onRouters based on
number of hopsnumber of hops
(D, V)
(Alternative routes are not kept.)
Netw
ork1
Netw
ork1(0hop
,e1)
Network 1Network 1
R1R1View of R1
e0
e2e1
Distance vector algorithms
they allow each device in the network to automatically build and maintain a local IP routing table. The principlebehind distance vector routing is simple.
Each router in the internetwork maintains the distance orcostfrom itself to every known destination. This valuerepresents the overall desirability of the path. Paths associated with a smaller cost value are more attractive to usethan paths associated with a larger value. The path represented by the smallest cost becomes the preferred pathto reach the destination. This information is maintained in a distance vector table.
The table is periodically advertised to each neighboring router. Each router processes these advertisements todetermine the best paths through the network.
-
8/22/2019 IP advanced.pdf
30/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 30
30
(no optimal route)
1- OverviewDistance vector : cost problem
NetworkNetwork11
R1R1
R2R2
R3R3
NetworkNetwork22
NetworkNetwork33
High throughput
High throughput
Low throughput
Network 3Network 3 (1 hop, R3)
Network 2Network 2 (0 hop, e1)
Network 1Network 1 (0 hop, e0)
R1R1
e0
e1
-
8/22/2019 IP advanced.pdf
31/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 31
31
1- OverviewLink state
NetworkNetwork11 NetworkNetwork
55
NetworkNetwork44R1R1
R2R2 R3R3
R4R4
NetworkNetwork22
NetworkNetwork33
NetworkNetwork11
R4R4
R3R3R2R2
NetworkNetwork
44
NetworkNetwork33
NetworkNetwork22
Network
Network55
Each router makes the network
topology
R1R1View of R1
Link state routing
The growth in the size and complexity of networks in recent years has necessitated the development of morerobust routing algorithms. These algorithms address the shortcoming observed in distance vector protocols. Thesealgorithms use the principle of a link state to determine network topology. A link state is the description of aninterface on a router (for example, IP address, subnet mask, type of network) and its relationship to neighboringrouters. The collection of these link states forms a link state database. The process used by link state algorithmsto determine network topology is straightforward:
Each router identifies all other routing devices on the directly connected networks.
Each router advertises a list of all directly connected network links and the associated cost of each link. This isperformed through the exchange of link state advertisements (LSAs) with other routers in the network.
Using these advertisements, each router creates a database detailing the current network topology. Thetopology database in each router is identical.
Each router uses the information in the topology database to compute the most desirable routes to eachdestination network. This information is used to update the IP routing table.
-
8/22/2019 IP advanced.pdf
32/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 32
32
2 classes of protocols:2 classes of protocols:
INTERNETINTERNET
1- OverviewVarious routing protocol classes
SprintSprintDFNDFN
RenaterRenater
Autonomous
system
IInteriornterior GGatewayateway PProtocolrotocol (RIP, IGRP, OSPF, )
EExteriorxterior GGatewayateway PProtocolrotocol (EGP, BGP, IS-IS, )
Autonomous
system
SphinxSphinx
JanetJanet
BGPBGP
(OSPF)
(RIP)
(OSPF)
(EIGRP)
(IGRP)
An AS is defined as a logical portion of a larger IP network. An AS is normally comprised of an internetwork withinan organization. It is administered by a single management authority.
Some routing protocols are used to determine routing paths within an AS. Others are used to interconnect a set ofautonomous systems:
Interior Gateway Protocols (IGPs): Interior gateway protocols allow routers to exchange informationwithin an AS. Examples of these protocols are Open Short Path First (OSPF) and Routing InformationProtocol (RIP).
Exterior Gateway Protocols (EGPs): Exterior gateway protocols allow the exchange of summaryinformation between autonomous systems. An example of this type of routing protocol is Border GatewayProtocol (BGP).
The interior protocols used to maintain routing information within each AS. The figure also shows the exteriorprotocols maintaining the routing information between autonomous systems.
Within an AS, multiple interior routing processes may be used. When this occurs, the AS must appear to otherautonomous systems as having a single, coherent interior routing plan. The AS must present a consistent view of
the internal destinations
-
8/22/2019 IP advanced.pdf
33/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 33
Alcatel University - 8AS 90200 1140 VT ZZA Ed.0133
Routing
2 RIP protocol
RFC 1058 and 1723
Routing Information Protocol (RIP)
RIP is an example of an interior gateway protocol designed for use within small autonomous systems.
In mid-1988, the IETF issued RFC 1058, which describes the standard operations of a RIP system. However, the RFCwas issued after many RIP implementations had been completed. For this reason, some RIP systems do not supportthe entire set of enhancements to the basic distance vector algorithm (for example, poison reverse and triggeredupdates).
-
8/22/2019 IP advanced.pdf
34/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 34
34
-
8/22/2019 IP advanced.pdf
35/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 35
35
RIP: router start-up
A B
C
D E
N1N1 N2N2
N6N6
N5N5
N3N3 N4N4
12
2
1
2
2
2
1
1
1
1
2
N1 11
0N3 3
20
Net HopCost
N1 12
0
N2 21
0N4 4
10
Net HopCost
N3 31
0
N6 62
0
Net HopCost
N5 51
0
N2 22
0
Net HopCost
N5 52
0
N6 61
0N4 4
20
Net HopCost
The distance vector table describes each destination network. The entries in
this table contain the following information:
The destination network (vector) described by this entry in the table.
The associated cost (distance) of the most attractive path to reach this destination. This provides theability to differentiate between multiple paths to a destination. In this context, the terms distance and costcan be misleading. They have no direct relationship to physical distance or monetary cost.
The IP address of the next-hop device used to reach the destination network.
At router initialization, each device contains a distance vector table listing each directly attached networks andconfigured cost. Typically, each network is assigned a cost of 1.
-
8/22/2019 IP advanced.pdf
36/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 36
36
IP@src
:3.2IP@
dest:broadcast
IP@src
:1.11.1IP@
dest:broadcast
N1 1
N3 1
RIP : Update of the routing tables (1)
N1 11
0
N3 32
0N1 1
20
N2 21
0
A B
C
D E
N1N1
N2N2
N6N6 N5N5
N3N3 N4N4
12
2
1
2
2
2
1
1
1
1
2
N4 41
0
N5 52
0
N6 61
0N4 4
20
N3 31
0
N6 62
0
N5 51
0
N2 22
0
Net HopCost Net HopCost
Net HopCost
Net HopCost
Net HopCost
N3 11
+1+1
N1 1
N1 1N3 1
1111
32
RIP packet types
The RIP protocol specifies two packet types. These packets may be sent by any device running the RIP protocol:
Request packets: A request packet queries neighboring RIP devices to obtain their distance vector table.The request indicates if the neighbor should return either a specific subset or the entire contents of thetable.
Response packets: A response packet is sent by a device to advertise the information maintained in itslocal distance vector table.
- The table is automatically sent every 30 seconds.
- The table is sent as a response to a request packet generated by another RIP node.
When a response packet is received by a device, the information contained in the update is compared against thelocal distance vector table. If the update contains a lower cost route to a destination, the table is updated to reflectthe new path.
-
8/22/2019 IP advanced.pdf
37/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 37
37
RIP : Update of the routing tables(2)
N1 11
0
N3 32
0N1 1
20
N2 21
0
A B
C
D E
N1N1
N2N2
N6N6 N5N5
N3N3 N4N4
12
2
1
2
2
2
1
1
1
1
2
N4 41
0
N5 52
0
N6 61
0N4 4
20
N3 31
0
N6 62
0
N5 51
0
N2 22
0
Net HopCost Net HopCost
Net HopCost
Net HopCost
Net HopCost
N3 1111
11
N1 32
1
N3 1
N6 1N1 2
+1
N3 62
1
N1 62
2
N3 1N6 1N1 2
+1
N6 31
1
-
8/22/2019 IP advanced.pdf
38/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 38
38
RIP : Update of the routing tables(3)
N1 11
0
N3 32
0N1 1
20
N2 21
0
A B
C
D E
N1N1
N2N2
N6N6 N5N5
N3N3 N4N4
12
2
1
2
2
2
1
1
1
1
2
N4 41
0
N5 52
0
N6 61
0N4 4
20
N3 31
0
N6 62
0
N5 51
0
N2 22
0
Net HopCost Net HopCost
Net HopCost
Net HopCost
Net HopCost
N3 1111
11
N1 32
1
N3 62
1
N1 62
2
N1 1
N2 1
N4 1N3 22
+1
N1 41
1
N2 41
1
N1 1N2 1N4 1
N3 22
N1 21
1N4 2
11
N3 2211
22
+1N6 3
11
-
8/22/2019 IP advanced.pdf
39/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 39
39
N2 61
2
N5 42
1
RIP : Update of the routing tables(4)
N1 11
0
N3 32
0N1 1
20
N2 21
0
A B
C
D E
N1N1
N2N2
N6N6 N5N5
N3N3 N4N4
12
2
1
2
2
2
1
1
1
1
2
N4 41
0
N5 52
0
N6 61
0N4 4
20
N3 31
0
N6 62
0
N5 51
0
N2 22
0
Net HopCost Net HopCost
Net HopCost
Net HopCost
Net HopCost
N3 1111
11
N1 32
1
N3 62
1
N1 41
1
N2 41
1
N5 1
N6 1N4 1N3 2
N1 2N2 2
N1 21
1N4 2
11
N3 2211
22
N6 52
1
+1
N5 1N6 1N4 1N3 2N1 2N2 2
+1
N6 31
1
N5 1N6 1N4 1N3 2N1 2N2 2
N5 61
1
N4 61
1
+1
N6 42 1
-
8/22/2019 IP advanced.pdf
40/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 40
40
N2 61
2
N5 42
1
RIP : Update of the routing tables(5)
N1 11
0N3 3
20
N1 12
0
N2 21
0
A B
C
D E
N1N1
N2N2
N6N6 N5N5
N3N3 N4N4
12
2
1
2
2
2
1
1
1
1
2
N4 41
0
N5 52
0
N6 61
0N4 4
20
N3 31
0
N6 62
0
N5 51
0
N2 22
0
Net HopCost Net HopCost
Net HopCost
Net HopCost
Net HopCost
N3 1111
11
N1 32
1
N3 62
1
N1 61
2N1 41
1
N2 41
1
N1 21
1N4 2
11
N3 2211
22
N6 52
1
N6 31
1
N5 61
1
N4 61
1
N6 42 1
N5 2
N1 1N2 1
N4 1N3 22
N6 2
+1
N5 2
N1 1
N2 1N4 1N3 22
N6 2
+1
N5 12 2
N2 12
1N4 1
21
N5 2
N1 1N2 1N4 1N3 22
N6 2
+1
-
8/22/2019 IP advanced.pdf
41/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 41
41
N2 61
2
N5 42
1
RIP : Update of the routing tables(6)
N1 11
0N3 3
20
N1 12
0
N2 21
0
A B
C
D E
N1N1
N2N2
N6N6 N5N5
N3N3 N4N4
12
2
1
2
2
2
1
1
1
1
2
N4 41
0
N5 52
0
N6 61
0N4 4
20
N3 31
0
N6 62
0
N5 51
0
N2 22
0
Net HopCost Net HopCost
Net HopCost
Net HopCost
Net HopCost
N3 1111
11
N1 32
1
N3 62
1
N1 61
2N1 41
1
N2 41
1
N1 21
1N4 2
11
N3 2211
22
N6 52
1
N6 31
1
N5 61
1
N4 61
1
N6 42 1N5 12 2
N2 12
1N4 1
21
N1 1
N3 1N6 2
N5 3
N2 2N4 2
N1 1
N3 1N6 2
N5 3
N2 2N4 2
+1
+1
-
8/22/2019 IP advanced.pdf
42/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 42
42
N2 61
2
N5 42
1
RIP : Update of the routing tables(7)
N1 12
0
N2 21
0
A B
C
D E
N1N1
N2N2
N6N6 N5N5
N3N3 N4N4
12
2
1
2
2
2
1
1
1
1
2
N4 41
0
N5 52
0
N6 61
0N4 4
20
N3 31
0
N6 62
0
Net HopCost
Net HopCost Net HopCost
N3 1111
11
N1 32
1
N3 62
1
N1 61
2N1 41
1
N2 41
1
N5 61
1
N4 61
1
N6 42 1+1
N5 1N2 1
N1 2
N4 2
N3 33N6 2
N5 1N2 1
N1 2N4 2N3 33
N6 2
+1
N1 11
0N3 3
20
Net HopCost
N6 31
1
N5 12 2
N2 12
1N4 1
21
N5 51
0
N2 22
0
Net HopCost
N1 21
1N4 2
11
N3 2211
22
N6 52
1
During an adverse condition, the length of time for every device in the network to produce an accurate routingtable is called the convergence time.
-
8/22/2019 IP advanced.pdf
43/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 43
43
RIP: slow convergence
B CAN1N1
30s
N1;N1;costcost=1=1
advertisementadvertisement
30s
N1;N1;costcost=2=2
advertisementadvertisement
In RIP the time convergence could be very long:
-
8/22/2019 IP advanced.pdf
44/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 44
44
The route selected by RIP is not the fastest
RIP: metric = hop count
A
B
C
2Mb/s2Mb/s
64kb/s64kb/s
2Mb/s2Mb/sN5N5
N4N4
N1N1 1
2
E1
Solution : Assign a minimum cost to a route
N2N2
N3N3
2
N6N6
1
21
N1 11
0
N2 21
0N3 3
10
Net HopCost
N4 22
1
N5 32
1
N6 22 1
-
8/22/2019 IP advanced.pdf
45/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 45
45
N2 61
2
N5 42
1
RIP: Failure in the network (1)
N1 12
0
N2 21
0
A B
C
D E
N1N1
N2N2
N6N6 N5N5
N3N3 N4N4
12
2
1
2
2
2
1
1
1
1
2
N4 41
0
N5 52
0
N6 61
0N4 4
20
N3 31
0
N6 62
0
N5 51
0
N2 22
0
Net HopCost
Net HopCost
Net HopCost
Net HopCost
N3 1111
11
N1 32
1
N3 62
1
N1 61
2N1 41
1
N2 41
1
N1 21
1N4 2
11
N3 2211
22
N6 52
1
N5 61
1
N4 61
1
N6 42 1
N1 11
0N3 3
20
Net HopCost
N6 31
1
N5 12 2
N2 12
1N4 1
21
N3 1N6 2
N5 2
N2 1
N4 1
N6 2
N5 2
N2 1N4 1
N6 2
+1
+1
+1
While the routing tables are converging, networks are susceptible to inconsistent routing behaviour. This cancause routing loops or other types of unstable packet forwarding.
-
8/22/2019 IP advanced.pdf
46/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 46
46
N2 61
2
N5 42
1
RIP: Failure in the network(2)
N1 12
0
N2 21
0
A B
C
D E
N1N1
N2N2
N6N6 N5N5
N3N3 N4N4
12
2
1
2
2
2
1
1
1
1
2
N4 41
0
N5 52
0
N6 61
0N4 4
20
N3 31
0
N6 62
0
N5 51
0
N2 22
0
Net HopCost
Net HopCost
Net HopCost
Net HopCost
N3 1111
11
N1 32
1
N3 62
1
N1 61
2N1 41
1
N2 41
1
N1 21
1N4 2
11
N3 2211
22
N6 52
1
N5 61
1
N4 61
1
N6 42 1
N1 11
N3 32
0
Net HopCost
N6 31
1
N5 12
N2 12
N4 12
N2 3
N3 1
N6 1
N5 2N4 2
+1
N2 3
N3 1N6 1
N5 2
N4 2
+1
231
331
231
-
8/22/2019 IP advanced.pdf
47/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 47
47
N2 61
2
N5 42
1
RIP: Failure in the network(3)
N1 12
0
N2 21
0
A B
C
D E
N1N1
N2N2
N6N6 N5N5
N3N3 N4N4
12
2
1
2
2
2
1
1
1
1
2
N4 41
0
N5 52
0
N6 61
0N4 4
20
N3 31
0
N6 62
0
N5 51
0
N2 22
0
Net HopCost
Net HopCost
Net HopCost
Net HopCost
N3 1111
N1 32
1
N3 62
1
N1 61
2N1 41
1
N2 41
1
N1 21
1N4 2
11
N3 2211
N6 52
1
N5 61
1
N4 61
1
N6 42 1
N1 11
N3 32
0
Net HopCost
N6 31
1
N5 31
N2 31
N4 31
2
2
3
N5 1N6 1N4 1N3 2
N1N2 2
N5 1
N6 1N4 1N3 2
N1N2 2
N5 1N6 1N4 1N3 2N1N1N2 2
+1
+1
224422
225522
+1
-
8/22/2019 IP advanced.pdf
48/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 48
48
Counting to infinity (1)
BA
N1N1 N2N2 N3N3
N1 11
N2 22
0
Net HopCost
N3 21
1
0
112 2
N1 22
N2 21
0
Net HopCost
N3 32
0
1
30s
30sRouting table broacasting
Routing table broacasting
Routing table broacasting
Routing table broacasting
-
8/22/2019 IP advanced.pdf
49/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 49
49
2.1broadcast
2.2broadcast
2.1broadcast
Counting to infinity(2)
BA
N1N1 N2N2 N3N3
112 2
t0
30s
N1 11N2 2
20
Net Hop Cost
N3 21
1
0 N1 22
N2 21
0Net HopCost
N3 32
0
1
30s
30s
N1 11N2 2
20
Net Hop Cost
N3 21 1
0
N1N2 1N3 1
2+1N1 1
1
N2 22 0
Net Hop Cost
N3 21 1
2
N1 22
N2 21
0
Net HopCost
N3 32
0
13N1N2 1N3 2
3
N1N2 1N3 1
4+1N1 21
N2 22 0
Net Hop Cost
N3 21 1
24
21
+1
Convergence and counting to infinity
Given sufficient time, this algorithm will correctly calculate the distance vector table on each device. However,during this convergence time, erroneous routes may propagate through the network.
The manner in which the costs in the distance vector table increment gives rise to the term counting to infinity. Thecosts continues to increment, theoretically to infinity. To minimize this exposure, whenever a network isunavailable, the incrementing of metrics through routing updates must be halted as soon as it is practical to do so.In a RIP environment, costs continue to increment until they reach a maximum value of 16. This limit is definedin the RFC.
A side effect of the metric limit is that it also limits the number of hops a packet can traverse from source networkto destination network. In a RIP environment, any path exceeding 15 hops is considered invalid. The routingalgorithm will discard these paths.
-
8/22/2019 IP advanced.pdf
50/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 50
50
2.1broadcast
Split horizon
BA
N1N1 N2N2 N3N3
112 2
t0
30s
N1 11N2 2
20
Net Hop Cost
N3 21
1
0 N1 22
N2 21
0Net HopCost
N3 32
0
1
30s
30s
N1 11N2 2
20
Net Hop Cost
N3 21 1
0
N3 1 +1N1 11N2 22 0
Net Hop Cost
N3 21 1
N1 22
N2 21
0
Net HopCost
N3 32
0
1
N1 22N2 22 0
Net Hop Cost
N3 21 1
2.2
broadcast
N1 1+1
2.1broadcast
N3 1 +1
2.2
broadcast+1
There are two enhancements to the basic distance vector algorithm that can minimize the counting to infinityproblem:
Split horizon with poison reverse
Triggered updates
These enhancements do not impact the maximum metric limit.
Split horizon
The excessive convergence time caused by counting to infinity may be reduced with the use of split horizon. Thisrule dictates that routing information is prevented from exiting the router on an interface through which theinformation was received.
The convergence occurs considerably faster using the split horizon rule. The limitation to this rule is that eachnode must wait for the route to the unreachable destination to time out before the route is removed from thedistance vector table. In RIP environments, this timeout is at least three minutes after the initial outage. During thattime, the device continues to provide erroneous information to other nodes about the unreachable destination.This propagates routing loops and other routing anomalies.
-
8/22/2019 IP advanced.pdf
51/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 51
51
Poison Reverse
BA
N1N1 N2N2 N3N3
112 2
t0
N1 11N2 2
20
Net Hop Cost
N3 21 1
0
N1 22
N2 21
0
Net HopCost
N3 32
0
1
N1 11N2 22 0
Net Hop Cost
N3 21 1
0N1
Poison reversePoison reverse
Split horizonSplit horizon
N1 22
N2 21
0
Net HopCost
N3 32
0
1-
N3 1 +1N1 11N2 22 0
Net Hop Cost
N3 21 1
0
30s
30s
N1 1
30s
30s
+1
Poison reverse
Poison reverse is an enhancement to the standard split horizon implementation. It is supported in RFC 1058. Withpoison reverse, all known networks are advertised in each routing update. However, those networks learnedthrough a specific interface are advertised as unreachable in the routing announcements sent out to that interface.
This drastically improves convergence time in complex, highly-redundant environments. With poison reverse,when a routing update indicates that a network is unreachable, routes are immediately removed from the routingtable. This breaks erroneous, looping routes before they can propagate through the network. This approach differsfrom the basic split horizon rule where routes are eliminated through timeouts.
Triggered updates
Like split horizon with poison reverse, algorithms implementing triggered updates are designed to reduce networkconvergence time. With triggered updates, whenever a router changes the cost of a route, it immediately sendsthe modified distance vector table to neighboring devices. This mechanism ensures that topology changenotifications are propagated quickly, rather than at the normal periodic interval.
-
8/22/2019 IP advanced.pdf
52/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 52
52
Hold-Down
BAN1N1 N2N2 N3N3
1
12 2
N1 11N2 2
20
Net Hop Cost
N3 21 1
N1 22N2 21
0
Net HopCost
N3 32
0
N1N1
1
/0
C1
N1N2 1
Net Cost
N3 2
1
N1N2 1
NetCost
N3 1
2
30s
N1N2 1
Net Cost
N3 2
1
N1N2 1
NetCost
N3 2
1
30s
66 Th.Th.
advertisementadvertisement
30s
N1N2 1
Net Cost
N3 1
2
N1N2
Net
N31
Cost
1
2
N1 22
N2 21
0
Net HopCost
N3 32
0
/11
N1 32N2 32
1
Net HopCost
N3 31
0
N1 32
N2 32
1
Net HopCost
N3 31
0
/22
End of failureEnd of failure
N1 22
N2 21
0
Net HopCost
N3 32
0
/1N1 3
2
N2 32
1
Net HopCost
N3 31
0
/2
N1 11
N2 22
0
Net Hop Cost
N3 21 1
/00
N1 11
N2 22
0
Net Hop Cost
N3 21
1
/0
N1 22
N2 21
0
Net HopCost
N3 32
0
/1
N1 32
N2 32
1
Net HopCost
N3 31
0
/2
Hold-down is the amount of time the router will wait before sending flashes about RIP changes. RIP has a 3-minute hold-down timer.
-
8/22/2019 IP advanced.pdf
53/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 53
53
Format of the RIP 1 message
0 8 16 24 31
Command Version
Address Family Id
Network 1 IP address
Metric (Distance to network 1)
1 : Request
2 : Response
Value 1 to 15Value 1 to 15
Version =1
2 for IP2 for IP
Address Family Id
Network 2 IP address
Metric (Distance to network 2)
RIP packet types
The RIP protocol specifies two packet types. These packets may be sent by any device running the RIP protocol: Request packets: A request packet queries neighboring RIP devices to obtain their distance vector table.
The request indicates if the neighbor should return either a specific subset or the entire contents of thetable.
Response packets: A response packet is sent by a device to advertise the information maintained in itslocal distance vector table.
RIPv1 does not manage subnet mask
-
8/22/2019 IP advanced.pdf
54/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 54
54
Encapsulation of the RIPv1 messages
Version Headerlength
Type OfService Datagram length
Identification Flag Datagram Offset
TTL Protocol: 1717 Checksum
Source IP address
Destination IPDestination IP addressaddress::
IPheader
UDPheader
UDP source port UDP destination port :
UDP message length Checksum UDP
RIP messageRIP message(25 routes maxi)(25 routes maxi)
512 bytesmax
UDPUDP
RIPRIP520520
BroadcastBroadcast255.255.255.255255.255.255.255
MAC src :--.--.--.--.--.--
MAC dest: ffff..ffff..ffff..ffff..ffff..ffff
-
8/22/2019 IP advanced.pdf
55/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 55
55
Advantages / disadvantages of RIPv1
Easy to implement,Easy to implement,
Easy to configure, to maintain, to useEasy to configure, to maintain, to use
Very useful in small networksVery useful in small networks
Vulnerable while convergence timeVulnerable while convergence time,,
Slow convergenceSlow convergence
Large bandwidth used by the protocolLarge bandwidth used by the protocol
Metric difficult to interpretMetric difficult to interpret
no multiple pathsno multiple paths
Arbitrary External route costsArbitrary External route costs
No managing of subnetsNo managing of subnets
No authentication of routing messagesNo authentication of routing messages
The main advantage of distance vector algorithms is that they are typically easy to implement and debug. Theyare very useful in small networks with limited redundancy.
RIP limitations
There are a number of limitations observed in RIP environments:
Path cost limits: The resolution to the counting to infinity problem enforces a maximum cost for a network path.This places an upper limit on the maximum network diameter. Networks requiring paths greater than 15 hops mustuse an alternate routing protocol.
Network-intensive table updates: Periodic broadcasting of the distance vector table can result in increasedutilization of network resources. This can be a concern in reduced-capacity segments.
Relatively slow convergence: RIP, like other distance vector protocols, is relatively slow to converge. Thealgorithms rely on timers to initiate routing table advertisements.
No support for variable length subnet masking: Route advertisements in a RIP environment do not includesubnet masking information. This makes it impossible for RIP networks to deploy variable length subnet masks.
-
8/22/2019 IP advanced.pdf
56/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 56
56
RIPv2
Allows subnet routingAllows subnet routing
Authentication of the routing messagesAuthentication of the routing messages
Multicast transmissionMulticast transmission
Advantages of RIPv2 compared with RIPv1 :Advantages of RIPv2 compared with RIPv1 :
RIP-2 is described in RFC 1723. The standard was published in late 1994.
-
8/22/2019 IP advanced.pdf
57/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 57
57
Multicast
MAC 00.6f.66.32.0b.0800.6f.66.32.0b.08MAC
00.53.27.32.02.c800.53.27.32.02.c8MAC MAC
00.18.55.92.a2.0800.18.55.92.a2.08
00.35.d6.39.00.35.d6.39.cbcb.0a.0a
DestDest :: 01.00.5e.00.00.09 ..01.00.5e.00.00.09 ..
00.80.9f.00.02.0300.80.9f.00.02.03MAC 01.00.5e.00.00.0901.00.5e.00.00.09
01.00.5e.00.00.0901.00.5e.00.00.09
For each multicast address, there exists a set of zero or more hosts that listen for packets transmitted to theaddress. This set of devices is called a host group.
224.0.0.9: All RIP2 routers
-
8/22/2019 IP advanced.pdf
58/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 58
58
Format of the RIP 2 message
0 8 16 24 31
Command Version1 : Request
2 : Response
Value 1 to 15Value 1 to 15
Version =2
Authentic type0: no authentic
2: Password data
Authentication data
2 for IP2 for IP
Address Family Id
x FF FF forauthentication entry
Address Family Id
Network 1 IP address
Subnet Mask
Next Hop
Metric (Distance to network 1)
Route tag
InternalInternal ororexternalexternal routeroute
RIP-2 is described in RFC 1723 it provides these additional benefits not available in RIP-1:
Support for CIDR and VLSM: RIP-2 supports supernetting (that is, CIDR) and variable-length subnet masking.This support was the major reason the new standard was developed. This enhancement positions the standard to
accommodate a degree of addressing complexity not supported in RIP-1.
Support for multicasting: RIP-2 supports the use of multicasting rather than simple broadcasting of routingannoucements. This reduces the processing load on hosts not listening for RIP-2 messages. To ensureinteroperability with RIP-1 environments, this option is configured on each network interface.
Support for authentication: RIP-2 supports authentication of any node transmitting route advertisements. Thisprevents fraudulent sources from corrupting the routing table.
Support for RIP-1: RIP-2 is fully interoperable with RIP-1. This provides backward-compatibility between thetwo standards.
The first entry in the update contains either a routing entry or an authentication entry.
- Route Tag: This field is intended to differentiate between internal and external routes. Internal routes arelearned via RIP-2 within the same network or AS.
- Subnet Mask: This field contains the subnet mask of the referenced network.
- Next Hop: This field contains a recommendation about the next hop the router should use when sendingdatagrams to the referenced network.
The RIP-2 standard does not encrypt the authentication password. It is transmitted in clear text. This makes thenetwork vulnerable to attack by anyone with direct physical access to the environment.
-
8/22/2019 IP advanced.pdf
59/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 59
59
Encapsulation of the RIPv2 messages
Version Headerlength
Type OfService Datagramme length
Identification Flag Datagramme Offset
TTL Protocol: 1717 Checksum
Source IP address
Destination IPDestination IP addressaddress::
IPheader
UDPheader
UDP source port UDP destination port :
UDP message length Checksum UDP
RIP messageRIP message(25 routes maxi)(25 routes maxi)
512 bytesmax
UDPUDP
RIPRIP520520
MulticastMulticast224.0.0.9224.0.0.9
MAC src :--.--.--.--.--.--
MAC dest: 01.00.5E.00.00.0901.00.5E.00.00.09
RIP uses a specific packet format to share information about the distances to known network destinations. RIPpackets are transmitted using UDP datagrams. RIP sends and receives datagrams using UDP port 520. RIPdatagrams have a maximum size of 512 octets.
Updates larger than this size must be advertised in multiple datagrams. In LAN environments, RIP datagrams aresent using the MAC all-stations broadcast address and an IP network broadcast address. In point-to-point or non-broadcast environments, datagrams are specifically addressed to the destination device.
A 512 byte packet size allows a maximum of 25 routing entries to be included in a single RIP advertisement.
-
8/22/2019 IP advanced.pdf
60/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 60
60
Relationship between IP and MAC in multicast mode
MulticastMulticast MACMAC addressaddress
1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 1
0 0 0 0 0 0 0 11 0 0 0 0 0 0 0 0 1 0 1 1 1 1 0 0 0
0 1 - 0 0 5 E- - - -
MulticastMulticast IPIP AddressAddress
Classe D
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 1
AddressAddress of groupof group
0 00 0 0 00 0 0 90 9
224 . .0 00 0 0 00 0 0 90 9.
AddressAddress translationtranslation
Multicast addressing
Multicast devices use Class D IP addresses to communicate. These addresses are contained in the rangeencompassing 224.0.0.0 through 239.255.255.255.
The mapping between the IP multicast destination address and the data-link address is not done with ARP.Instead, a static mapping has been defined. In an Ethernet network, multicasting is supported if the high-orderoctet of the data-link address is 0x'01'. The IANA has reserved the range 0x01005E000000' through0x'01005E7FFFFF' for multicast addresses. This range provides 23 usable bits. The 32-bit multicast IP address ismapped to an Ethernet address by placing the low-order 23 bits of the Class D address into the low-order 23 bitsof the IANA reserved address block.
-
8/22/2019 IP advanced.pdf
61/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 61
61
netid2
netid1
netid3netid4
CISCO : RIP Configuration
R2#
R2(config)#
config terminal
routerrip
R2(config-router)#
Routing protocol
R2
R3
R1
netid5
R2(config-router)#version 2 RIPv2
network
R2(config-router)# network
R2(config-router)# network
RIP routing updates will be sent and
received only through interfaces on
these networks
router rip : Enable a RIP routing process
network network-number :Associate a network with a RIP routing process. RIP routing updates will be sent and received onlythrough interfaces on this network. RIP sends updates to the interfaces in the specified networks. Also, if an interfaces network isnot specified, it will not be advertised in any RIP update.
version 2 : RIP v2 supports authentication, key management, route summarization, classless interdomain routing (CIDR), andvariable-length subnet masks (VLSMs).
no auto-summary Disable automatic summarization. RIP Version 2 supports automatic route summarization by default. Thesoftware summarizes subprefixes to the classful network boundary when crossing classful network boundaries. If you havedisconnected subnets, disable automatic route summarization to advertise the subnets.
Static routes that point to an interface will be advertised via RIP, IGRP, and other dynamic routing protocols, regardless of whetherredistribute static router configuration commands were specified for those routing protocols. These static routes are advertisedbecause static routes that point to an interface are considered in the routing table to be connected and hence lose their staticnature. However, if you define a static route to an interface that is not one of the networks defined in a network command, nodynamic routing protocols will advertise the route unless a redistribute static command is specified for these protocols.
-
8/22/2019 IP advanced.pdf
62/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 62
62
Interface configuration
OnlyOnly one router onone router on thisthis LANLAN((broadcastingbroadcasting of RIPof RIP
messages notmessages not requiredrequired))
RIPRIP should be implementedshould be implemented ininthisthis hosthost havinghaving 2 interfaces in2 interfaces inorderorder to selectto select thethe best routebest route
OnlyOnly one routerone routeronon thisthis LAN but,LAN but,
Passive-interface
PSTN
static route
Example: (config)# router rip
(config-router)# network network-to-be-advertised
(config-router)# network network-to-be- advertised
(config-router)# passive-interface interface
RIP modes of operation
RIP hosts have two modes of operation:
Active mode: Devices operating in active mode advertise their distance vector table and also receive routingupdates from neighboring RIP hosts. Routing devices are typically configured to operate in active mode.
Passive (or silent) mode: Devices operating in this mode simply receive routing updates from neighboring RIPdevices. They do not advertise their distance vector table. End stations are typically configured to operate inpassive mode.
-
8/22/2019 IP advanced.pdf
63/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 63
63
CISCO : Show RIP protocol
#show ip protocolsRouting Protocol is "rip"
Sending updates every 30 seconds, next due in 13 seconds
Invalid after 180 seconds, hold down 180, flushed after 240
Outgoing update filter list for all interfaces is
Incoming update filter list for all interfaces is
Redistributing: rip
Default version control: send version 1, receive any version
Interface Send Recv Key-chain
Ethernet0 1 1 2
Ethernet1 1 1 2
Routing for Networks:
172.16.0.0
Routing Information Sources:
Gateway Distance Last Update
172.16.200.4 120 00:00:22
172.16.200.1 120 00:00:12
172.16.200.3 120 00:00:07
172.16.200.200 120 00:00:05
Distance: (default is 120)
Weight added to the original metric which is function
of routing protocol : RIP120, OSPF110, IGRP100, ...
Next routing table transmissionRouting table
broadcastedevery 30
Route becomesinvalid after 180
without information
After the end offailure, the routekept invalid 180
When a route becomesinvalid (metric=16),router keeps it in
memory during 240
Administrative distance is the feature used by routers to select the best path when there are two or more different routes to thesame destination from two different routing protocols. Administrative distance defines the reliability of a routing protocol. Each
routing protocol is prioritized in order of most to least reliable (believable) using an administrative distance value. Administrative distance is the first criterion that a router uses to determine which routing protocol to use. The smaller the
administrative distance value, the more reliable the protocol.
If two protocols provide route information for the same destination.When several routing protocols are implemented in CISCOrouter, it adds a distance (weight) to the original metric, RIP: 120, OSPF:110, IGRP:100. If there are two routes with the samemetric to a destination, example: one got by Rip and another by Ospf, the router will select the ospf route,
The Cisco IOS software sends routing information updates every 30 seconds; this process is termed advertising.
If a router does not receive an update from another router for 180 seconds or more, it marks the routes served by the nonupdatingrouter as being unusable.
If there is still no update after 240 seconds, the router removes all routing table entries for the nonupdating router.
-
8/22/2019 IP advanced.pdf
64/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 64
64
r202#
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default
U - per-user static route, o - ODR
T - traffic engineered route
Gateway of last resort is not set
172.16.0.0/24 is subnetted, 14 subnets
R 172.16.204.0 [120/1] via 172.16.200.4, 00:00:00, Ethernet0
C 172.16.200.0 is directly connected, Ethernet0R 172.16.201.0 [120/1] via 172.16.200.1, 00:00:20, Ethernet0
C 172.16.202.0 is directly connected, Ethernet1
R 172.16.203.0 [120/1] via 172.16.200.3, 00:00:14, Ethernet0
R 172.16.1.0 [120/1] via 172.16.200.200, 00:00:14, Ethernet0
show ip route
CISCO : show IP route
If two protocols provide route information for the same destination.When several routing protocols are implemented in CISCOrouter, it adds a administrative distance (weight) to the original metric, RIP: 120, OSPF:110, IGRP:100. If there are two routes withthe same metric to a destination, example: one got by Rip and another by Ospf, the router will select the ospf route,
Connected interface 0
Static route 1
Enhanced Interior Gateway Routing Protocol (EIGRP) summary route 5
External Border Gateway Protocol (BGP) 20
Internal EIGRP 90
IGRP 100
OSPF 110
Intermediate System-to-Intermediate System (IS-IS) 115
Routing Information Protocol (RIP) 120
Exterior Gateway Protocol (EGP) 140
On Demand Routing (ODR) 160
External EIGRP 170
Internal BGP 200
Unknown* 255
-
8/22/2019 IP advanced.pdf
65/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 65
65
CISCO : Debug RIP events
r202#deb ip rip events
RIP event debugging is on
r202#
00:45:46: RIP: received v1 update from 172.16.200.4 on Ethernet0
00:45:46: RIP: Update contains 1 routes00:45:52: RIP: sending v1 update to 255.255.255.255 via Ethernet0 (172.16.200.2)
00:45:52: RIP: Update contains 1 routes
00:45:52: RIP: Update queued
00:45:52: RIP: sending v1 update to 255.255.255.255 via Ethernet1 (172.16.202.1)
00:45:52: RIP: Update sent via Ethernet0
00:45:52: RIP: Update contains 13 routes
00:45:52: RIP: Update queued
00:45:52: RIP: Update sent via Ethernet1
00:45:57: RIP: received v1 update from 172.16.200.1 on Ethernet0
00:45:57: RIP: Update contains 1 routes
00:46:02: RIP: received v1 update from 172.16.200.200 on Ethernet0
00:46:02: RIP: Update contains 9 routes
00:46:05: RIP: received v1 update from 172.16.200.3 on Ethernet000:46:05: RIP: Update contains 1 routes
r202#u all
-
8/22/2019 IP advanced.pdf
66/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 66
66
CISCO : Debug RIP
r202#deb ip ripRIP protocol debugging is onr202#00:46:24: RIP: received v1 update from 172.16.200.1 on Ethernet000:46:24: 172.16.201.0 in 1 hops00:46:31: RIP: received v1 update from 172.16.200.200 on Ethernet000:46:31: 172.16.1.0 in 1 hops00:46:31: 172.16.2.0 in 1 hops
00:46:31: 172.16.104.0 in 3 hops00:46:31: 172.16.105.0 in 3 hops00:46:31: 172.16.106.0 in 3 hops00:46:31: 172.16.100.0 in 2 hops00:46:31: 172.16.101.0 in 3 hops00:46:31: 172.16.102.0 in 3 hops00:46:31: 172.16.103.0 in 3 hops00:46:34: RIP: received v1 update from 172.16.200.3 on Ethernet000:46:34: 172.16.203.0 in 1 hops00:46:43: RIP: received v1 update from 172.16.200.4 on Ethernet000:46:43: 172.16.204.0 in 1 hops00:46:46: RIP: sending v1 update to 255.255.255.255 via Ethernet0 (172.16.200.2)00:46:46: subnet 172.16.202.0, metric 100:46:46: RIP: sending v1 update to 255.255.255.255 via Ethernet1 (172.16.202.1)00:46:46: subnet 172.16.204.0, metric 200:46:46: subnet 172.16.200.0, metric 100:46:46: subnet 172.16.201.0, metric 200:46:46: subnet 172.16.203.0, metric 200:46:46: subnet 172.16.1.0, metric 2
00:46:46: subnet 172.16.2.0, metric 200:46:46: subnet 172.16.104.0, metric 400:46:46: subnet 172.16.105.0, metric 400:46:46: subnet 172.16.106.0, metric 400:46:46: subnet 172.16.100.0, metric 300:46:46: subnet 172.16.101.0, metric 400:46:46: subnet 172.16.102.0, metric 400:46:46: subnet 172.16.103.0, metric 400:46:52: RIP: received v1 update from 172.16.200.1 on Ethernet000:46:52: 172.16.201.0 in 1 hops
-
8/22/2019 IP advanced.pdf
67/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 67
Alcatel University - 8AS 90200 1140 VT ZZA Ed.0167
Routing
3. OSPF protocol
Open Shortest Path First (OSPF)
The Open Shortest Path First (OSPF) protocol is another example of an interior gateway protocol. It was developed as a non-proprietary routing alternative to address the limitations of RIP. Initial development started in 1988 and was finalized in 1991.Subsequent updates to the protocol continue to be published. The current version of the standard is documented in RFC 2328.
OSPF provides a number of features not found in distance vector protocols. Support for these features has made OSPF a widely-deployed routing protocol in large networking environments. In fact, RFC 1812 Requirements for IPv4 Routers, lists OSPF as theonly required dynamic routing protocol.
Equal cost load balancing: The simultaneous use of multiple paths may provide more efficient utilization of network resources.
Logical partitioning of the network: This reduces the propagation of outage information during adverse conditions. It also provides theability to aggregate routing announcements that limit the advertisement of unnecessary subnet information.
Support for authentication: OSPF supports the authentication of any node transmitting route advertisements. This prevents fraudulentsources from corrupting the routing tables.
Faster convergence time: OSPF provides instantaneous propagation of routing changes. This expedites the convergence timerequired to update network topologies.
Support for CIDR and VLSM: This allows the network administrator to efficiently allocate IP address resources.
-
8/22/2019 IP advanced.pdf
68/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 68
68
NetworkNetwork
222.211.10222.211.10.00
NetworkNetwork
192.213.11192.213.11.00
Network : 128.213Network : 128.213.0.0.0.0
Shortest path tree
RbRb
RdRd
RcRc
Each router makes a tree-representation of the network
RaRa (view of R1)RaRa
NetworkNetwork
128.213128.213.0.0.0.0
LinkLink--costcost= 100 000 000 / bandwidthbps
55
55
1010
RbRb
1010
RcRc
1010
1010
NetworkNetwork
192.213.11192.213.11.00
55
NetworkNetwork222.211.10222.211.10.00
RdRd
55
55
1010
costcost
00
costcost
The SPF algorithm is used to process the information in the topology database. It provides a tree-representation of the network.The device running the SPF algorithm is the root of the tree. The output of the algorithm is the list of shortest-paths to each
destination network. Because each router is processing the same set of LSAs, each router creates an identical link state database. However,
because each device occupies a different place in the network topology, application of the SPF algorithm produces a differenttree for each router.
cost= 100 000 000 / bandwidthbps
Example :
Cost of 10Mb/s Ethernet link : 108 / 107 = 10
Cost of link T1 1,544Mb/s: 108 / 1544x103 = 64
-
8/22/2019 IP advanced.pdf
69/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 69
69
From To L CostFrom To L Cost
From To L Cost
SPF database (Initialisation)
RbRb
RdRd
RcRc
RaRa
Net: 3Net: 3
Net: 2Net: 2
Net: 1Net: 1
11
11
11
22
22
22
33
AA B 1B 111 33AA C 1C 111 33
From To L Cost
C3
C1
C1
C3
C2
C3
C4
Toutes les Databases sont identiques
AA NN11 1111 33
CC A 1A 133 22CC B 1B 133 22
CC NN11 1133 22CC NN33 3322 11
CC D 3D 322 11
DD B 2B 222 44DD C 3C 311 33
DD NN33 3311 33
BB A 1A 122 11
BB D 2D 211 33
BB NN11 1122 11BB NN22 2211 33
BB C 1C 122 11
DD NN22 2222 44
Link state database
The link state database is also called the topology database. It contains the set of link state advertisements describing theOSPF network and any external connections.
-
8/22/2019 IP advanced.pdf
70/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 70
70
From To L Cost
From To L Cost
SPF database (Updating)
RbRb
RdRd
RcRc
RaRa
Net: 3Net: 3
Net: 2Net: 2
Net: 1Net: 1
11
11
11
22
22
22
33
AA B 1B 111 33AA C 1C 111 33
From To L Cost
C3
C1
C1
C3
C2
C3
C4
All the Databases are identical
AA NN11 1111 33
From To L Cost
CC A 1A 133 22CC B 1B 133 22
CC NN11 1133 22CC NN33 3322 11
CC D 3D 322 11
BB A 1A 122 11
BB D 2D 211 33CC NN11 1133 22
DD B 2B 222 44DD C 3C 311 33
CC A 1A 133 22
DD NN33 3311 33
BB NN11 1122 11BB NN22 2211 33
CC D 3D 322 11CC NN33 3322 11
DD NN22 2222 44
CC B 1B 133 22
BB C 1C 122 11
DD B 2B 222 44DD C 3C 311 33
DD NN33 3311 33
BB A 1A 122 11BB C 1C 122 11
BB NN11 1122 11BB NN22 2211 33
BB D 2D 211 33
CC A 1A 133 22CC B 1B 133 22
CC NN11 1133 22CC NN33 3322 11
AA B 1B 111 33AA C 1C 111 33
AA NN11 1111 33CC D 3D 322 11
BB A 1A 122 11
BB D 2D 211 33
BB NN11 1122 11BB NN22 2211 33
BB C 1C 122 11
AA B 1B 111 33AA C 1C 111 33
AA NN11 1111 33
CC NN11 1133 22
DD B 2B 222 44DD C 3C 311 33
CC A 1A 133 22
DD NN33 3311 33
CC D 3D 322 11CC NN33 3322 11
DD NN22 2222 44
CC B 1B 133 22
DD NN22 2222 44
DD B 2B 222 44DD C 3C 311 33
BB A 1A 122 11BB C 1C 122 11
AA B 1B 111 33AA C 1C 111 33
AA NN11 1111 33
DD NN33 3311 33
BB NN11 1122 11BB NN22 2211 33
BB D 2D 211 33
DD NN22 2222 44
Each router within the area maintains an identical copy of the link state database.
-
8/22/2019 IP advanced.pdf
71/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 71
71CC
AA BB CC DD
AA BB CC DD
BB
CC
DD
AA
BB
AA BB CC DD
BB CC DD
Route
A to
Route
Route
SPF calculation
From To L Cost
RaRaAA B 1B 111 33AA C 1C 111 33
AA NN11 1111 33
BB A 1A 122 11
BB D 2D 211 33CC NN11 1133 22
DD B 2B 222 44DD C 3C 311 33
CC A 1A 133 22
DD NN33 3311 33
BB NN11 1122 11BB NN22 2211 33
CC D 3D 322 11CC NN33 3322 11
DD NN22 2222 44
CC B 1B 133 22
BB
C 1C 122 11
33 3300
00 1111 33
112222
44 33
00
00
3+3+00 3+3+113+3+11 3+3+33
A,B
C=3
A,C
C=3
A,B,DC=6
3+3+113+3+223+3+22 3+3+00
A,C,DC=4
+3+3+3+3
RbRb
RdRd
RcRc
Net: 3Net: 3
Net: 2Net: 2
Net: 1Net: 1
11
11
11
22
22
22
33
C3
C1
C1
C3
C2
C3
C4
primaryprimary
secondarysecondary
There are two algorithms for computing a routing table from a link table. These are:
the forward search algorithm (Also known as Dijkstra's Algorithm) and,
the backward search algorithm (Also known as the Bellman-Ford Algorithm)
-
8/22/2019 IP advanced.pdf
72/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 72
72
SPF example : Network topology
slipslip
11
E12E12
E15E15
N3N3
E12E12 E13E13 E14E14N1N1
N2N2 N4N4
N9N9
N12N12
N11N11
N8N8
N7N7
R1R1
R2R2 R3R3
R4R4 R5R5
R9R9
R12R12
N10N10
R11R11
R7R7
R8R8
R6R6
N6N6R10R10
8888
88 88 88
77
6688
11
33
11
11
11
101022
11 2211
11
44
55
77
66
66
22
99
22
33
33
1133
11
11
66
Inter networks example:
-
8/22/2019 IP advanced.pdf
73/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 73
73
SPF example : Init
E12E12 E13E13 E14E14
8888
88 88 88
77
88
11
1010
22
11 2211
11
44
E12E12
E15E15
55
77
66
66
22
99
22
33
R1R1
R2R2 R3R3
R4R4 R5R5
R9R9
R12R12R11R11
R7R7
R8R8
R6R6
N6N61133 R10R10
11
11
66
N3N3
N2N2
33N1N1
33 N11N11
N9N9
N10N10 N12N12
N8N8
N4N4
11
11
11
Dest Cost
R6R6R10R10 77R6R6R3R3 66R6R6R5R5 66
N7N7
66
Dest Cost
R3R3R6R6 88R3R3N4N4 22R3R3N3N3 11
Dest Cost
R4R4
R5R5 88R4R4N3N3 11
Dest Cost
R1R1N1N1 33R1R1N3N3 11
Dest Cost
R2R2N2N2 33R2R2N3N3 11
Dest Cost
R9R9N11N11 33R9R9N9N9 11
Dest Cost
R12R12N9N9 11
R12R12N10N10 22R12R12N12N12 1010
Dest Cost
R11R11N9N9 11R11R11N8N8 22
Dest Cost
R10R10R6R6 55R10R10N6N6 11R10R10N8N8 33
Dest Cost
R8R8N6N6 11R8R8N7N7 44
Dest Cost
R7R7R5R5 66
R7R7N6N6 11R7R7E12E12 22R7R7E16E16 99
Dest Cost
R5R5R4R4 88R5R5R6R6 77R5R5R7R7 66R5R5E12E12 88R5R5E13E13 88R5R5E14E14 88
Each node knows the directly connected links as well as the adjacent routers.
-
8/22/2019 IP advanced.pdf
74/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 74
74
SPF example : Database exchange
E12E12 E13E13 E14E14
8888
88 88 88
77
88
11
1010
22
11 2211
11
44
E12E12
E15E15
55
77
66
66
22
99
22
33
R1R1
R2R2 R3R3
R4R4 R5R5
R9R9
R12R12R11R11
R7R7
R8R8
R6R6
N6N61133 R10R10
11
11
66
N3N3
N2N2
33N1N1
33 N11N11
N9N9
N10N10 N12N12
N8N8
N4N4
11
11
11
N7N7
66
R6R6Dest Cost
R6R6R10R10 77R6R6R3R3 66R6R6R5R5 66R3R3R6R6 88R3R3N4N4 22
R3R3N3N3 11R2R2N2N2 33R2R2N3N3 11R1R1N1N1 33R1R1N3N3 11R4R4R5R5 88R4R4N3N3 11R9R9N11N11 33R9R9N9N9 11R12R12N9N9 11R12R12N10N10 22R12R12N12N12 1010R11R11N9N9 11R11R11N8N8 22R10R10R6R6 55R10R10N6N6 11R10R10N8N8 33R8R8N6N6 11
R8R8N7N7 44R7R7R5R5 66R7R7N6N6 11R7R7E12E12 22R7R7E15E15 99R5R5R4R4 88R5R5R6R6 77R5R5R7R7 66R5R5E12E12 88R5R5E13E13 88R5R5E14E14 88
After exchanges between routers, each router within the area maintains an identical copy of the link state database.
-
8/22/2019 IP advanced.pdf
75/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 75
75
SPF example : Graph
E12E12 E13E13 E14E1488 88 88
E12E12
E15E15
22
99
R1R1
R2R2 R3R3
R4R4 R5R5
R9R9
R12R12R11R11
R7R7
R8R8
R6R6
N6N6R10R10
N3N3
N2N2
N1N1
N11N11
N9N9
N10N10 N12N12
N8N8
N4N4
N7N7
88
66
11
11
22 22
11
1133
33
11
11
33
33 11
1188
88
66
66
557733
33
1111
11
11
11
11
1010
101022
22
22
22
33
33
11
11
1111
4444
1111
7766
R6R6Dest Cost
R6R6R10R10 77R6R6R3R3 66R6R6R5R5 66R3R3R6R6 88R3R3N4N4 22
R3R3N3N3 11R2R2N2N2 33R2R2N3N3 11R1R1N1N1 33R1R1N3N3 11R4R4R5R5 88R4R4N3N3 11R9R9N11N11 33R9R9N9N9 11R12R12N9N9 11R12R12N10N10 22R12R12N12N12 1010R11R11N9N9 11R11R11N8N8 22R10R10R6R6 55R10R10N6N6 11R10R10N8N8 33R8R8N6N6 11
R8R8N7N7 44R7R7R5R5 66R7R7N6N6 11R7R7E12E12 22R7R7E15E15 99R5R5R4R4 88R5R5R6R6 77R5R5R7R7 66R5R5E12E12 88R5R5E13E13 88R5R5E14E14 88
From its topology database, any router can know the network topology.
-
8/22/2019 IP advanced.pdf
76/306
-
8/22/2019 IP advanced.pdf
77/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 77
77
SPF example : Routing table of R6
E13E13 E14E14
88 88
E12E12E15E15
99
R1R1
R2R2R3R3
R4R4R5R5
R9R9
R12R12
R11R11
R7R7
R8R8
R6R6
N6N6R10R10
N3N3
N2N2
N1N1
N11N11
N9N9
N10N10 N12N12
N8N8
N4N4
N7N7
11
11
66
33
33
6622
77
33
33
11
11
1010
22
11
44
22
Dest. Next Costhop
N1 R3 10
N2 R3 10
N3 R3 7
N4 R3 8N6 R10 8
N7 R10 12
N8 R10 10
N9 R10 11
N10 R10 13
N11 R10 14
N12 R10 21
RT5 R5 6
RT7 R10 8
E12 R10 10
E13 R5 14
N14 R5 14
N15 R10 17
22
11
11
1111
11
Routing tables are constructed by examining a link table whose entries detail the cost of each link in the network.
-
8/22/2019 IP advanced.pdf
78/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 78
78
SPF example : Tree seen by R6
E13E13 E14E14
E12E12 E15E15
R1R1 R2R2
R3R3
R4R4
R5R5
R9R9 R12R12
R11R11 R7R7R8R8
R6R6
N6N6
R10R10
N3N3
N2N2N1N1
N11N11
N9N9
N10N10 N12N12
N8N8
N4N4 N7N7
Each router can see the network as a tree.
-
8/22/2019 IP advanced.pdf
79/306
Alcatel University - 8AS 90200 1140 VH ZZA Ed.01 Page 79
79
OSPF: Router Identifier
IP@= 3.3.3.3IP@= 3.3.3.3
IP@=1.1.1.1IP@=1.1.1.1
IP@=2.2.2.2IP@=2.2.2.2
LoopbackLoopback
IP@= 5.5.5.5IP@= 5.5.5.5
LoopbackLoopbackIP@= 7.7.7.7IP@= 7.7.7.7
IP@= 9.9.9.9IP@= 9.9.9.9
IP@=4.4.4.4IP@=4.4.4.4
RID=RID=
if no loopback,
RID=RID=
RID= (Router ID) highest loopback IP@,
the highest interface IP@.
7.7.7.77.7.7.7
3.3.3.33.3.3.3
In OSPF, an unique identifier is assigned to each node : RID (Router Identity)
The RID is the highest IP address on the box or the loopback interface, calculated at boot time or whenever the OSPF processis restarted.
-
8/2