presentation network routing rip pnni 2
TRANSCRIPT
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Routing
Institute of IT
University of Peshawar
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Connectionless Forwarding
Each router (switch) makes a LOCALdecision to forward the packet towards B
A B
R1 R4
R2
R3
R6
R7
R5
R8
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Connectionless Forwarding
This is termed destination-basedconnectionless forwarding
How does each router know the correct local forwarding decision for any possible destination
address?
Knowledge of the topology state of the network
AND
knowledge is maintained by a routing protocol
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Routing Protocols
Distribute the knowledge ofthe currenttopology state ofthe networktoallrouters
This knowledge is used by each router togenerate a forwarding table, which
contains the local switching decisionfor each known destination address
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Routing Protocols
ManagementofqualitynetworkServicesrequires:
accuracyofthe routinginformation
dynamic adjustmentofthe routinginformation
matchingaggregate traffic flow tonetworkcapacity
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Exterior routing
ISP Routing Tasks
customers
internal
peer / upstream
Interior routing
Customer routing
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Interior Routing
Discovers the topology of a networkthrough the operationof a distributedrouting protocol
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A
20
10
4
10
40
5
6
10
15
10
5
B
5
5
45
R1 R4
R2
R3
R6
R
R5
R8
Path Selection
Minimum cost from A to B is 39 units
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A
20
10
4
10
40
5
6
15
10
5
B
5
5
45
R1 R4
R2
R3
R6
R
R5
R8
Dynamic Path Adjustment
IfR5 R7 breaks, minimum cost path from A to B is
Now 46 units
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Interior Routing Protocols
Describe the currentnetwork topology
Routing protocols distribute how to reachaddress prefix groups where
Routing protocols function through either Distributed computing model (distance vector)
Parallel computing model (link state)
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Routing Protocols
Distance Vector Routing Protocols
Each node sends its routing table (dest,distance) to all neighbors every 30 seconds
Lower distances are updated with the
neighbor as next hop
cannot scalecannot resolve routing loops
quicklyRIPis the main
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Routing Protocols
Link State Routing Protocols Each link, the connected nodes and the metric is flooded
to all routers
Each link up/down status change is incrementallyflooded
Each router re-computes the routing table in parallelusing the common link state database
OSPF is the main protocol in use today
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Interior and Exterior
Routing Protocols
Exterior Routing Space
Interior
Route
Space
InteriorRoute
Space
Interior
Route
Space
Interior
Route
Space
Interior
Route
Space
AS1 AS1221
AS2402
AS3561
AS701
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The Routing Process(NOT A Simple Process)
HOST A
172.16.10.2
HOST B
172.16.20.2
Ethernet 0
172.16.10.1
Ethernet 1
172.16.20.1
A simple scenario of two host and one
router where HOST Apings Hosts B IPAddress
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HOST A
172.16.10.2
HOST B
172.16.20.2
Ethernet 0
172.16.10.1
Ethernet 1
172.16.20.1
The Routing Process(NOT A Simple Process)
STEP 01: ICMP creates an ECHO Message Payload
STEP 02: ICMP hands over the payload to Internet Protocol for creating a
packet(source ,destin address and protocolfield) that tell the host to
whom it should hand the payload when the destination is reached
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HOST A
172.16.10.2
HOST B
172.16.20.2
Ethernet 0
172.16.10.1
Ethernet 1
172.16.20.1
The Routing Process(NOT A Simple Process)
STEP 03: After packet creation IP works with ARP to determine whether
the destination IP host is on the same network or other(Remote in this case)
STEP 04: Since result of step 03 is remote host, the packet is send to the
default gateway The registry in the Windows is parsed to find the
configured default gateway.
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HOST A
172.16.10.2
HOST B
172.16.20.2
Ethernet 0
172.16.10.1
Ethernet 1
172.16.20.1
The Routing Process(NOT A Simple Process)
STEP 05: The default gateway of host A(172.16.10.2) is configured to 172.16.10.1but to send this packet HARDWARE Address of router Ethernet 0 is to be
known so that the packet can be handed over to Data Link Layer
STEP 06: So address Step 05, ARP cache is checked to see if the IP
address of the default gateway is resolved to hardware address
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HOST A
172.16.10.2
HOST B
172.16.20.2
Ethernet 0
172.16.10.1
Ethernet 1
172.16.20.1
The Routing Process(NOT A Simple Process)
STEP 06 (a): if have packet is send to Data link for framing
STEP 06(b): if not ARP broadcast of Local network for h/w addressof 172.16.10.1. The router responds and the host caches the address.
The router also caches the h/w address of Host A in ARP Cache
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HOST A
172.16.10.2
HOST B
172.16.20.2
Ethernet 0
172.16.10.1
Ethernet 1
172.16.20.1
The Routing Process(NOT A Simple Process)
STEP 7: At DLink Layer , LAN driver is used to provide media access A FRAis generated
STEP 8: Once frame is completed . Handed over to physical layer to be
put on the physical medium
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HOST A
172.16.10.2
HOST B
172.16.20.2
Ethernet 0
172.16.10.1
Ethernet 1
172.16.20.1
The Routing Process(NOT A Simple Process)
STEP 9: Bits received by every device in the network and builds the frame andbuild CRC to check answer in the FCS.. If crc matched then H/w destination
address is checked to see if it is matched and if so. Then ethernet type field is
checked to find the protocol used
STEP 10: Packet is pulled from the frame and frame is discarded
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HOST A
172.16.10.2
HOST B
172.16.20.2
Ethernet 0
172.16.10.1
Ethernet 1
172.16.20.1
The Routing Process(NOT A Simple Process)
STEP 11: IP receives check IP address since doesnt match router looks
For the destination network address in its routing table
STEP 12:if no entry of the network in the routing table an ICMP messag
to HOST A with message of destination Network not available