cis 185 ccnp route ch. 4 manipulating routing updates
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CIS 185 CCNP ROUTECh. 4 Manipulating Routing Updates
Rick Graziani
Cabrillo College
graziani@cabrillo.edu
Last Updated: Fall 2011
2
Materials
Book: Implementing Cisco IP Routing
(ROUTE) Foundation Learning Guide: Foundation learning for the ROUTE 642-902 Exam
By Diane Teare Book
ISBN-10: 1-58705-882-0 ISBN-13: 978-1-58705-882-0
eBook ISBN-10: 0-13-255033-4 ISBN-13: 978-0-13-255033-8
Network Performance Issues
Common network performance issues include the following: Excessive routing updates:
Decrease network performance CPU utilization spikes The size of the routing update The frequency of the updates
The presence of any route maps or filters: Incorrectly configured route maps or filters can cause too much or the
wrong data to be sent. The number of routing protocols running in the same AS:
Processing the updates. Routes may also be redistributed between protocols, which can add to
the number of updates that a specific protocol must process.3
Controlling routing updates involves a variety of solutions, including the: Design changes:
Limiting the number of routing protocols used Choice of routing protocol Network design (areas, stub networks, etc.)
Using passive interfaces Route filtering using:
Access lists Route maps Distribute lists Prefix lists 4
Route Redistribution
5
Routing protocols were not designed to interoperate with one another using different: Metrics Reactions to topology changes Timers Processes
Routers using different routing protocols can exchange routing information. Route redistribution is the capability of boundary routers connecting
different routing domains to exchange and advertise routing information between those routing domains. 6
7
Route Redistribution
One-way route redistribution - one protocol receives the routes from another)
Two-way route redistribution - both protocols receive routes from each other.
Boundary routers:Boundary routers: Routers that perform redistribution Borders two or more ASs or routing domains. Note: The term boundary routerboundary router is also sometimes used to
describe a router running a classful routing protocol (like RIP) that has interfaces in more than one classful network.
Redistribution is always performed outbound The router doing redistribution does not change its routing table.
Router A (boundary router) participates in both: OSPF EIGRP
Two-way redistribution does not affect the routing table on Router A However:
Router C will learn about redistributed EIGRP networks (via OSPF) Router B will learn about redistributed OSPF networks (via EIGRP)
Only networks in Router A’s routing table can be redistributed.8
Why configure redistribution? Company mergers and different IGPs are used Company has different divisions with the network under separate
control for business or political reasons Company has connections between business partners To allow multivendor interoperability (OSPF on non-Cisco, EIGRP
on Cisco, for instance)
Route Redistribution
Incompatible routing information Each routing protocol uses different metrics.
EIGRP uses slowest BW and cumulative Delay OSPF use cumulative BW
Metrics cannot be translated exactly into a different protocol Path selection may not be optimal.
Potential Routing loops – Depending on how redistribution is used, routers can send routing information received from one AS back into the AS. (Route Feedback)
Inconsistent convergence times: Different routing protocols converge at different rates.
These potential trouble spots can be avoided with careful planning and implementation.
Configuring Redistribution
My best path to 192.100.10.0 is this way.
My best path to 192.100.10.0 is this way.
192.168.10.0
EIGRP
OSPFRouting Loop!
R3
R2
R1
R2 and R3 are running both OSPF and EIGRP
Selecting the Best Route in a Redistribution Environment Cisco routers use the
following two parameters to select the best path:
Administrative distance: Trustworthiness of the
routing source Modifying the
administrative distance to influence the route-selection process is discussed later
When using route redistribution, you might occasionally need to modify a protocol’s administrative distance so that it is preferred and to prevent routing loops. (later)
Routing metric: Best path
11
Concepts of Redistribution
Multiple Routing Processes
RTA#show running-config router ospf 24 network 10.2.0.0 0.0.255.255 area 0!router ospf 46 network 192.168.2.0 0.0.0.255 area 2!router eigrp 53 network 172.16.0.0 network 172.17.0.0!router eigrp 141 network 10.0.0.0 network 192.168.3.0
Not usually recommended
Not usually recommended
Cisco routers support up to 30 dynamic routing processes on a single router.
Most routing protocols allow an administrator to configure multiple processes of the same routing algorithm
RIP and BGP are notable exceptions.
Route redistribution - The process of exchanging routing information between routing protocols. EIGRP routing domain learns about networks in OSPF routing
domain. OSPF routing domain learns about networks in EIGRP routing
domain. Done by a boundary router which participates in both routing protocols.
Route Redistribution
Redistribution Concepts and Processes
The redistribution command (“take routes from”) Configured on the boundary router. Participates in both routing protocols. Independent of any one protocol Various complexities depending on the routing protocols and
the options.
Router(config-router)# redistribute from-protocol [process-id]
Note: Other parameters may be required and will be discussed.
I run both EIGRP and OSPF.
Redistributing from OSPF into EIGRP
Our Topology
Boundary router R2-E-O is running: EIGRP for 172.30.0.0 subnets and 172.31.0.0 network OSPF for 172.16.0.0 subnets and 172.17.0.0 network 192.168.1.0 or 10.0.0.0 not currently included in either routing
protocol (more on this later)
EIGRP 1 OSPF 1
Redistribution into EIGRP
The syntax differs slightly depending on the routing protocol into which routes will be redistributed.
redistribute protocol [process-id | as-number] [metric bw delay reliability load mtu ] [match {internal | nssa-external | external 1 | external 2}] [tag tag-value] [route-map name]
19
Redistribution into EIGRP
protocol - The source of routing information. Includes RIP, OSPF, EIGRP, IS-IS, BGP, connected, and static.
process-id, as-number - If redistributing a routing protocol that uses a process-id or ASN on the router global config command, use this parameter to refer to that process or ASN value.
metric - A keyword after which follows the four metric components (bandwidth, delay, reliability, link load), plus the MTU associated with the route.
match - If redistributing from OSPF, this keyword lets you match internal OSPF routes, external (by type), and NSSA external routes, essentially filtering which routes are redistributed.
tag - Assigns a unitless integer value to the route, which can be later matched by other routers using a route-map.
route-map - Apply the logic in the referenced route-map to filter routes, set metrics, and set route tags.
redistribute protocol [process-id | as-number] [metric bw delay reliability load mtu ] [match {internal | nssa-external | external 1 | external 2}] [tag tag-value] [route-map name]
Redistribution into EIGRP
Current configurations
R1-E
router eigrp 1
network 172.30.0.0
network 172.31.0.0
auto-summary
R2-E-O
router eigrp 1
network 172.30.0.0
auto-summary
router ospf 1
network 172.16.0.0 0.0.0.3 area 0
R3-O
router ospf 1
network 172.16.0.0 0.0.255.255 area 0
R4-O
router ospf 1
network 172.16.0.0 0.0.255.255 area 0
network 172.17.0.0 0.0.255.255 area 0
Redistribution into EIGRP
R1-E# show ip route
C 172.31.0.0/16 is directly connected, Loopback31
172.30.0.0/16 is variably subnetted, 6 subnets, 3 masks
C 172.30.2.0/24 is directly connected, FastEthernet0/1
C 172.30.3.0/24 is directly connected, Loopback0
C 172.30.0.0/30 is directly connected, Serial0/0
D 172.30.0.0/16 is a summary, 00:02:41, Null0
C 172.30.1.0/24 is directly connected, FastEthernet0/0
C 172.30.4.0/24 is directly connected, Loopback1
R1-E#
What do you expect to see?
Directly Connected and any EIGRP networks – NO OSPF networks
What networks do I know about and how did I learn about them?
Redistribution into EIGRP
R2-E-O# show ip route
O 172.17.0.0/16 [110/846] via 172.16.0.1, 00:02:32, Serial0/1
172.16.0.0/16 is variably subnetted, 4 subnets, 2 masks
O 172.16.0.4/30 [110/845] via 172.16.0.1, 00:02:32, Serial0/1
C 172.16.0.0/30 is directly connected, Serial0/1
O 172.16.1.0/24 [110/782] via 172.16.0.1, 00:02:32, Serial0/1
O 172.16.2.0/24 [110/846] via 172.16.0.1, 00:02:32, Serial0/1
D 172.31.0.0/16 [90/20640000] via 172.30.0.1, 00:03:46, Serial0/0
172.30.0.0/16 is variably subnetted, 5 subnets, 2 masks
D 172.30.2.0/24 [90/20514560] via 172.30.0.1, 01:22:36, Serial0/0
D 172.30.3.0/24 [90/20640000] via 172.30.0.1, 01:22:36, Serial0/0
C 172.30.0.0/30 is directly connected, Serial0/0
D 172.30.1.0/24 [90/20514560] via 172.30.0.1, 01:22:36, Serial0/0
D 172.30.4.0/24 [90/20640000] via 172.30.0.1, 01:22:36, Serial0/0
10.0.0.0/24 is subnetted, 1 subnets
C 10.0.0.0 is directly connected, FastEthernet0/1
C 192.168.1.0/24 is directly connected, FastEthernet0/0
R2-E-O#
What do you expect to see?EIGRP and OSPF networks What networks
do I know about and how did I learn about them?
Redistribution into EIGRP
R3-O# show ip route
O 172.17.0.0/16 [110/65] via 172.16.0.6, 00:09:06, Serial0/2
172.16.0.0/16 is variably subnetted, 4 subnets, 2 masks
C 172.16.0.4/30 is directly connected, Serial0/2
C 172.16.0.0/30 is directly connected, Serial0/1
C 172.16.1.0/24 is directly connected, FastEthernet0/0
O 172.16.2.0/24 [110/65] via 172.16.0.6, 00:09:06, Serial0/2
R3-O#
What do you expect to see?
Only OSPF networks – NO EIGRP networks
What networks do I know about and how did I learn about them?
Redistribution into EIGRP
R4-O# show ip route
C 172.17.0.0/16 is directly connected, FastEthernet0/1
172.16.0.0/16 is variably subnetted, 4 subnets, 2 masks
C 172.16.0.4/30 is directly connected, Serial0/0
O 172.16.0.0/30 [110/128] via 172.16.0.5, 00:09:52, Serial0/0
O 172.16.1.0/24 [110/65] via 172.16.0.5, 00:09:52, Serial0/0
C 172.16.2.0/24 is directly connected, FastEthernet0/0
R4-0#
What do you expect to see?
Only OSPF networks – NO EIGRP networks
What networks do I know about and how did I learn about them?
Redistribution into EIGRP
No change for R1-E! No OSPF networks Let’s see what happened (or didn’t happen)…
R2-E-O(config)# router eigrp 1
R2-E-O(config-router)# redistribute ospf 1
R1-E# show ip route
C 172.31.0.0/16 is directly connected, Loopback31
172.30.0.0/16 is variably subnetted, 6 subnets, 3 masks
C 172.30.2.0/24 is directly connected, FastEthernet0/1
C 172.30.3.0/24 is directly connected, Loopback0
C 172.30.0.0/30 is directly connected, Serial0/0
D 172.30.0.0/16 is a summary, 00:02:41, Null0
C 172.30.1.0/24 is directly connected, FastEthernet0/0
C 172.30.4.0/24 is directly connected, Loopback1
R1-E#
I will redistribute my OSPF learned networks (and OSPF network command networks) into EIGRP, telling my EIGRP neighbors about these networks
Hey! I don’t see any of the networks in the OSPF domain! What happened?
26
Redistribution into EIGRP
R2-E-O# show ip route
O 172.17.0.0/16 [110/846] via 172.16.0.1, 00:02:32, Serial0/1
172.16.0.0/16 is variably subnetted, 4 subnets, 2 masks
O 172.16.0.4/30 [110/845] via 172.16.0.1, 00:02:32, Serial0/1
C 172.16.0.0/30 is directly connected, Serial0/1
O 172.16.1.0/24 [110/782] via 172.16.0.1, 00:02:32, Serial0/1
O 172.16.2.0/24 [110/846] via 172.16.0.1, 00:02:32, Serial0/1
D 172.31.0.0/16 [90/20640000] via 172.30.0.1, 00:03:46, Serial0/0
172.30.0.0/16 is variably subnetted, 5 subnets, 2 masks
D 172.30.2.0/24 [90/20514560] via 172.30.0.1, 01:22:36, Serial0/0
D 172.30.3.0/24 [90/20640000] via 172.30.0.1, 01:22:36, Serial0/0
C 172.30.0.0/30 is directly connected, Serial0/0
D 172.30.1.0/24 [90/20514560] via 172.30.0.1, 01:22:36, Serial0/0
D 172.30.4.0/24 [90/20640000] via 172.30.0.1, 01:22:36, Serial0/0
10.0.0.0/24 is subnetted, 1 subnets
C 10.0.0.0 is directly connected, FastEthernet0/1
C 192.168.1.0/24 is directly connected, FastEthernet0/0
R2-E-O#
Should R2’s routing table change? No
27
Redistribution into EIGRP
R2-E-O(config)# router eigrp 1
R2-E-O(config-router)# redistribute ospf 1
R2-E-O# show ip eigrp top
IP-EIGRP Topology Table for AS(1)/ID(192.168.1.1)
P 172.30.2.0/24, 1 successors, FD is 20514560
via 172.30.0.1 (20514560/28160), Serial0/0
P 172.30.3.0/24, 1 successors, FD is 20640000
via 172.30.0.1 (20640000/128256), Serial0/0
P 172.30.0.0/30, 1 successors, FD is 20512000
via Connected, Serial0/0
P 172.31.0.0/16, 1 successors, FD is 20640000
via 172.30.0.1 (20640000/128256), Serial0/0
P 172.30.1.0/24, 1 successors, FD is 20514560
via 172.30.0.1 (20514560/28160), Serial0/0
P 172.30.4.0/24, 1 successors, FD is 20640000
via 172.30.0.1 (20640000/128256), Serial0/0
For now notice that there are no “OSPF networks” in R2’s topology table.
They are still in the routing table because R2 also runs OSPF, but this is an EIGRP command.
Redistribution into EIGRP
When redistributing into EIGRP from another routing protocol you must convert the other routing protocol’s metric (OSPF’s cost, bandwidth) into EIGRP’s metric (BW, DLY, Reliability and Load).
This metric, referred to as the seed or default metric, is defined during redistribution configuration.
Three methods: Metric parameter with redistribute command
Sets the default for all redistribute commands Default-metric command
Sets the default for all redistribute commands Route-map
Sets different metrics for routes learned from a single source
redistribute protocol [process-id | as-number] [metric bw delay reliability load mtu ]
default-metric bw delay reliability load mtu
BW/DLY BW
Redistribution into EIGRP
router eigrp 1
network 172.20.0.0
redistribute ospf 1
redistribute eigrp 2
default-metric 10000 100 255 1 1500
redistribute rip metric 50000 500 255 1 1500
EIGRP 1 EIGRP 2
OSPF 1
RIP
default-metricdefault-metric command is used where the metric parameter is not being applied in the redistribute command.
metricmetric parameter takes precedence over the default-metricdefault-metric command Note: The metric will give all redistributed networks the same starting
metric. This is known as the seed metric
50000 500 255 1
10000 100 255 1
Redistribution into EIGRP
Note: MTU is NOT one of the EIGRP metrics (never has been, never will
be) MTU is included because it is tracked through the path to find the
smallest MTU.
R2-E-O(config)# router eigrp 1
R2-E-O(config-router)# redistribute ospf 1
R2-E-O(config-router)# default-metric 1000 33 255 1 1500
R2-E-O(config)# router eigrp 1
R2-E-O(config-router)# redistribute ospf 1 metric 1000 33 255 1 1500
ORBW DLY RLY Load MTU
BW DLY RLY Load MTU
1000 33 255 1
31
Redistribution into EIGRP
New Entries
R2-E-O# show ip eigrp top
IP-EIGRP Topology Table for AS(1)/ID(192.168.1.1)
P 172.16.0.4/30, 1 successors, FD is 2568448
via Redistributed (2568448/0)
P 172.16.0.0/30, 1 successors, FD is 2568448
via Redistributed (2568448/0)
P 172.16.1.0/24, 1 successors, FD is 2568448
via Redistributed (2568448/0)
P 172.17.0.0/16, 1 successors, FD is 2568448
via Redistributed (2568448/0)
P 172.16.2.0/24, 1 successors, FD is 2568448
via Redistributed (2568448/0)
All the redistributed routes have the same feasible distance (FD) calculation (2568448), because all use the same component metrics per the configured default-metric command
EIGRP topology table lists the outgoing interface as "via redistributed"
32
Redistribution into EIGRP
R2-E-O# show ip eigrp top 172.16.0.0/30
IP-EIGRP (AS 1): Topology entry for 172.16.0.0/30
State is Passive, Query origin flag is 1, 1 Successor(s), FD is 2568448
Routing Descriptor Blocks:
0.0.0.0, from Redistributed, Send flag is 0x0
Composite metric is (2568448/0), Route is External
Vector metric:
Minimum bandwidth is 1000 Kbit
Total delay is 330 microseconds
Reliability is 255/255
Load is 1/255
Minimum MTU is 1500
Hop count is 0
External data:
Originating router is 192.168.1.1 (this system)
AS number of route is 1
External protocol is OSPF, external metric is 0
Administrator tag is 0 (0x00000000)
From default-metric command
"(this system)", meaning that the router on which the command was issued (R2 in this case) redistributed the route.
Redistribution into EIGRP
R1-E# show ip route
D EX 172.17.0.0/16 [170/3080448] via 172.30.0.2, 00:01:50, Serial0/0
172.16.0.0/16 is variably subnetted, 4 subnets, 2 masks
D EX 172.16.0.4/30 [170/3080448] via 172.30.0.2, 00:01:50, Serial0/0
D EX 172.16.0.0/30 [170/3080448] via 172.30.0.2, 00:01:50, Serial0/0
D EX 172.16.1.0/24 [170/3080448] via 172.30.0.2, 00:01:50, Serial0/0
D EX 172.16.2.0/24 [170/3080448] via 172.30.0.2, 00:01:50, Serial0/0
C 172.31.0.0/16 is directly connected, Loopback31
172.30.0.0/16 is variably subnetted, 6 subnets, 3 masks
C 172.30.2.0/24 is directly connected, FastEthernet0/1
C 172.30.3.0/24 is directly connected, Loopback0
C 172.30.0.0/30 is directly connected, Serial0/0
D 172.30.0.0/16 is a summary, 00:12:08, Null0
C 172.30.1.0/24 is directly connected, FastEthernet0/0
C 172.30.4.0/24 is directly connected, Loopback1
EX: External Route (redistributed) 170: Administrative distance (90 for EIGRP internal
routes) R1-E has the same metric (3080448) for all external
EIGRP networks (from the OSPF domain)
Great! Now I see all the networks in the OSPF domain but as EIGRP routes.
34
Redistribution into EIGRP
R2 redistributed into EIGRP the routes learned via OSPF and its own directly connected network 172.16.0.0/30. But not 192.168.1.0/24 and 10.0.0.0/8 This is because 172.16.0.0/30 is an OSPF enabled interface (network
statement) Redistribute command, redistributes the following:
All routes in the routing table learned by that routing protocol All connected routes of interfaces on which that routing protocol is
enabled Otherwise must be redistributed another way (connected or static) – coming
R2-E-O# show ip eigrp top
P 172.16.0.0/30, 1 successors, FD is 2568448
via Redistributed (2568448/0)
Redistribution into EIGRP
Two ways to redistribute 10.0.0.0/24 network. Redistribute Connected Add OSPF network command
Also propagates 10.0.0.0/24 throughout OSPF domain
R2-E-O(config)# router ospf 1
R2-E-O(config-router)# network 10.0.0.0 0.0.0.255 area 0
R2-E-O# show ip route
10.0.0.0/24 is subnetted, 1 subnets
C 10.0.0.0 is directly connected, FastEthernet0/1
No change to routing table
What about the 10.0.0.0/24 network? How can I redistribute it into EIGRP?
Redistribution into EIGRP
10.0.0.0 is now redistributed into the EIGRP domain with the rest of the OSPF networks.
R1-E# show ip route
D EX 10.0.0.0 [170/3080448] via 172.30.0.2, 00:01:33, Serial0/0
R4-0# show ip route
O 10.0.0.0 [110/129] via 172.16.0.5, 00:04:02, Serial0/0
The 10.0.0.0 network is now included as one of my EIGRP routes.
Redistribution into EIGRP
192.168.1.0/24 is redistributed into EIGRP as a connected network. metric option is not required for this command (default 0, but beyond the scope of this
pres.) 192.168.1.0/24 is redistributed into the EIGRP domain using the default metric but
it is NOT propagated throughout OSPF domain
R2-E-O(config)# router eigrp 1
R2-E-O(config-router)# redistribute connected metric 1000 33 255 1 1500
R1-E# show ip route
10.0.0.0/24 is subnetted, 1 subnets
D EX 10.0.0.0 [170/3080448] via 172.30.0.2, 00:01:57, Serial0/0
D EX 192.168.1.0/24 [170/3080448] via 172.30.0.2, 00:01:57, Serial0/0
R1-E#
What about the 192.168.1.0 network? How can I redistribute it into EIGRP?
Redistribution into EIGRP
Where we left off…
R2: Currently
router eigrp 1
network 172.30.0.0
auto-summary
redistribute ospf 1
default-metric 1000 33 255 1 1500
redistribute connected 1000 33 255 1 1500
!
router ospf 1
network 10.0.0.0 0.0.0.255 area 0
network 172.16.0.0 0.0.0.3 area 0
Redistributing from EIGRP into OSPF
Redistribution into OSPF
Several similarities and differences to redistributing into EIGRP. In this case we must convert the EIGRP metric to the Cisco OSPF
metric of Bandwidth.
BW/DLY BW
redistribute protocol [process-id | as-number] [metric {metric-value | transparent}] [metric-type type-value] [match {internal | external 1 | external 2 | nssa-external}] [tag tag-value] [route-map map-tag] [subnets]
41
Redistribution into OSPF
Metric - Defines the cost metric assigned to the route in the Type 5 (or Type 7 if NSSA) LSA. metric transparent when taking from another OSPF process, pass through the metric with the route.
metric-type {1 | 2} - Defines the external metric type of 1 (E1 routes) or 2 (E2 routes).
Match - If redistributing from OSPF, this keyword lets you match internal OSPF routes, external (by type), and NSSA external routes, essentially filtering which routes are redistributed.
Tag - Assigns a unitless integer value to the route, which can be later matched by other routers using a route-map.
route-map - Apply the logic in the referenced route-map to filter routes, set metrics, and set route tags.
Subnets - Redistribute subnets of classful networks. Without this parameter, only routes for classful networks are redistributed. (This behavior is particular to the OSPF redistribute command.)
redistribute protocol [process-id | as-number] [metric {metric-value | transparent}] [metric-type type-value] [match {internal | external 1 | external 2 | nssa-external}] [tag tag-value] [route-map map-tag] [subnets]
Redistribution into OSPF
Defaults when redistributing into OSPF: When redistributing networks from all other sources the default
metric is 20. External metric type 2 (metric does not change throughout OSPF
routing domain) Only redistributes routes of classful (Class A, B, and C) networks,
and not for subnets
BW/DLY BW=20 BW=20
redistribute protocol [process-id | as-number] [metric {metric-value | transparent}] [metric-type type-value] [match {internal | external 1 | external 2 | nssa-external}] [tag tag-value] [route-map map-tag] [subnets]
Redistribution into OSPF
Where we left off…
R2: Currently
router eigrp 1
network 172.30.0.0
auto-summary
redistribute ospf 1
default-metric 1000 33 255 1 1500
redistribute connected 1000 33 255 1 1500
!
router ospf 1
network 10.0.0.0 0.0.0.255 area 0
network 172.16.0.0 0.0.0.3 area 0
Redistribution into OSPF
R2-E-O# show ip route
O 172.17.0.0/16 [110/846] via 172.16.0.1, 00:02:32, Serial0/1
172.16.0.0/16 is variably subnetted, 4 subnets, 2 masks
O 172.16.0.4/30 [110/845] via 172.16.0.1, 00:02:32, Serial0/1
C 172.16.0.0/30 is directly connected, Serial0/1
O 172.16.1.0/24 [110/782] via 172.16.0.1, 00:02:32, Serial0/1
O 172.16.2.0/24 [110/846] via 172.16.0.1, 00:02:32, Serial0/1
D 172.31.0.0/16 [90/20640000] via 172.30.0.1, 00:03:46, Serial0/0
172.30.0.0/16 is variably subnetted, 5 subnets, 2 masks
D 172.30.2.0/24 [90/20514560] via 172.30.0.1, 01:22:36, Serial0/0
D 172.30.3.0/24 [90/20640000] via 172.30.0.1, 01:22:36, Serial0/0
C 172.30.0.0/30 is directly connected, Serial0/0
D 172.30.1.0/24 [90/20514560] via 172.30.0.1, 01:22:36, Serial0/0
D 172.30.4.0/24 [90/20640000] via 172.30.0.1, 01:22:36, Serial0/0
10.0.0.0/24 is subnetted, 1 subnets
C 10.0.0.0 is directly connected, FastEthernet0/1
C 192.168.1.0/24 is directly connected, FastEthernet0/0
R2-E-O#
What do you expect to see?EIGRP and OSPF networks What networks
do I know about and how did I learn about them?
45
Redistribution into OSPF
No External Type 5 LSAs No EIGRP networks being redistributed into OSPF
R2-E-O# show ip ospf data
OSPF Router with ID (192.168.1.1) (Process ID 1)
Router Link States (Area 0)
Link ID ADV Router Age Seq# Checksum Link count
172.16.1.1 172.16.1.1 85 0x80000005 0x006220 5
172.30.0.6 172.30.0.6 2000 0x80000006 0x006BB4 4
192.168.1.1 192.168.1.1 1117 0x80000003 0x009742 3
R2-E-O#
Redistribution into OSPF
By default, only classful networks will be redistributed from EIGRP into OSPF. Subnets will not be redistributed Supernets will also be redistributed (such as 173.0.0.0/8)
R2-E-O(config)# router ospf 1
R2-E-O(config-router)# redistribute eigrp 1
% Only classful networks will be redistributed
R2-E-O(config-router)#
R2-E-O# show ip ospf data
<Router Link States omitted>
Type-5 AS External Link States
Link ID ADV Router Age Seq# Checksum Tag
172.31.0.0 192.168.1.1 9 0x80000001 0x0094D4 0
R2-E-O#
47
Redistribution into OSPF
R2-E-O# show ip route
O 172.17.0.0/16 [110/846] via 172.16.0.1, 00:03:56, Serial0/1
172.16.0.0/16 is variably subnetted, 4 subnets, 2 masks
O 172.16.0.4/30 [110/845] via 172.16.0.1, 00:03:56, Serial0/1
C 172.16.0.0/30 is directly connected, Serial0/1
O 172.16.1.0/24 [110/782] via 172.16.0.1, 00:03:56, Serial0/1
O 172.16.2.0/24 [110/846] via 172.16.0.1, 00:03:56, Serial0/1
D 172.31.0.0/16 [90/20640000] via 172.30.0.1, 00:18:29, Serial0/0
172.30.0.0/16 is variably subnetted, 5 subnets, 2 masks
D 172.30.2.0/24 [90/20514560] via 172.30.0.1, 01:37:19, Serial0/0
D 172.30.3.0/24 [90/20640000] via 172.30.0.1, 01:37:19, Serial0/0
C 172.30.0.0/30 is directly connected, Serial0/0
D 172.30.1.0/24 [90/20514560] via 172.30.0.1, 01:37:19, Serial0/0
D 172.30.4.0/24 [90/20640000] via 172.30.0.1, 01:37:19, Serial0/0
10.0.0.0/24 is subnetted, 1 subnets
C 10.0.0.0 is directly connected, FastEthernet0/1
C 192.168.1.0/24 is directly connected, FastEthernet0/0
Remember, routes are onlyRedistributed if they are in theRouting table
Redistribution into OSPF
Only the class B network 172.31.0.0/16 is redistributed into OSPF
R3-O# show ip route
O 172.17.0.0/16 [110/65] via 172.16.0.6, 00:01:16, Serial0/2
172.16.0.0/16 is variably subnetted, 4 subnets, 2 masks
C 172.16.0.4/30 is directly connected, Serial0/2
C 172.16.0.0/30 is directly connected, Serial0/1
C 172.16.1.0/24 is directly connected, FastEthernet0/0
O 172.16.2.0/24 [110/65] via 172.16.0.6, 00:01:16, Serial0/2
O E2 172.31.0.0/16 [110/20] via 172.16.0.2, 00:01:16, Serial0/1
10.0.0.0/24 is subnetted, 1 subnets
O 10.0.0.0 [110/65] via 172.16.0.2, 00:01:17, Serial0/1
R3-O#
I only see the class B 172.31.0.0/16 network in the EIGRP domain.
49
Redistribution into OSPF
External Type 5 LSA
R3-O# show ip ospf data
<Router Link States omitted>
Type-5 AS External Link States
Link ID ADV Router Age Seq# Checksum Tag
172.31.0.0 192.168.1.1 88 0x80000001 0x0094D4 0
R3-O#
Redistribution into OSPF
Subnets – Subnets are now included in the redistribution.
R2-E-O(config)# router ospf 1
R2-E-O(config-router)# redistribute eigrp 1 subnets
No warning message “Only classful networks will be redistributed”
I will add the subnets option.
51
Redistribution into OSPF
R2 now includes Type 5 LSAs for subnets
R2-E-O# show ip ospf data
Type-5 AS External Link States
Link ID ADV Router Age Seq# Checksum Tag
172.30.0.0 192.168.1.1 79 0x80000001 0x008EDE 0
172.30.1.0 192.168.1.1 79 0x80000001 0x0095D3 0
172.30.2.0 192.168.1.1 79 0x80000001 0x008ADD 0
172.30.3.0 192.168.1.1 79 0x80000001 0x007FE7 0
172.30.4.0 192.168.1.1 79 0x80000001 0x0074F1 0
172.31.0.0 192.168.1.1 220 0x80000001 0x0094D4 0
R2-E-O#
Redistribution into OSPF – E2
R3-O#show ip route
O 172.17.0.0/16 [110/65] via 172.16.0.6, 00:13:41, Serial0/2
172.16.0.0/16 is variably subnetted, 4 subnets, 2 masks
C 172.16.0.4/30 is directly connected, Serial0/2
C 172.16.0.0/30 is directly connected, Serial0/1
C 172.16.1.0/24 is directly connected, FastEthernet0/0
O 172.16.2.0/24 [110/65] via 172.16.0.6, 00:13:41, Serial0/2
O E2 172.31.0.0/16 [110/20] via 172.16.0.2, 00:13:41, Serial0/1
172.30.0.0/16 is variably subnetted, 5 subnets, 2 masks
O E2 172.30.2.0/24 [110/20] via 172.16.0.2, 00:00:12, Serial0/1
O E2 172.30.3.0/24 [110/20] via 172.16.0.2, 00:00:12, Serial0/1
O E2 172.30.0.0/30 [110/20] via 172.16.0.2, 00:00:12, Serial0/1
O E2 172.30.1.0/24 [110/20] via 172.16.0.2, 00:00:14, Serial0/1
O E2 172.30.4.0/24 [110/20] via 172.16.0.2, 00:00:14, Serial0/1
10.0.0.0/24 is subnetted, 1 subnets
O 10.0.0.0 [110/65] via 172.16.0.2, 00:00:14, Serial0/1
External OSPF routes are E2 with a default cost of 20.
metric-type E2 - The cost of a type 2 route is always the external cost, irrespective of the interior cost to reach that route.
BW=20
Now I see all networks and subnets from the EIGRP domain.
Redistribution into OSPF
R4-0# show ip route
C 172.17.0.0/16 is directly connected, FastEthernet0/1
172.16.0.0/16 is variably subnetted, 4 subnets, 2 masks
C 172.16.0.4/30 is directly connected, Serial0/0
O 172.16.0.0/30 [110/128] via 172.16.0.5, 00:04:02, Serial0/0
O 172.16.1.0/24 [110/65] via 172.16.0.5, 00:04:02, Serial0/0
C 172.16.2.0/24 is directly connected, FastEthernet0/0
O E2 172.31.0.0/16 [110/20] via 172.16.0.5, 00:04:02, Serial0/0
172.30.0.0/16 is variably subnetted, 5 subnets, 2 masks
O E2 172.30.2.0/24 [110/20] via 172.16.0.5, 00:01:46, Serial0/0
O E2 172.30.3.0/24 [110/20] via 172.16.0.5, 00:01:46, Serial0/0
O E2 172.30.0.0/30 [110/20] via 172.16.0.5, 00:01:46, Serial0/0
O E2 172.30.1.0/24 [110/20] via 172.16.0.5, 00:01:46, Serial0/0
O E2 172.30.4.0/24 [110/20] via 172.16.0.5, 00:01:46, Serial0/0
10.0.0.0/24 is subnetted, 1 subnets
O 10.0.0.0 [110/129] via 172.16.0.5, 00:04:04, Serial0/0
External OSPF routes are E2 with a default cost of 20.
metric-type 2 - The cost of a type 2 route is always the external cost, irrespective of the interior cost to reach that route.
BW=20 BW=20
54
Redistribution into OSPF
R4 now includes Type 5 LSAs for subnets
R4-0# show ip ospf data
Type-5 AS External Link States
Link ID ADV Router Age Seq# Checksum Tag
172.30.0.0 192.168.1.1 113 0x80000001 0x008EDE 0
172.30.1.0 192.168.1.1 113 0x80000001 0x0095D3 0
172.30.2.0 192.168.1.1 113 0x80000001 0x008ADD 0
172.30.3.0 192.168.1.1 113 0x80000001 0x007FE7 0
172.30.4.0 192.168.1.1 113 0x80000001 0x0074F1 0
172.31.0.0 192.168.1.1 254 0x80000001 0x0094D4 0
R4-0#
Redistribution into OSPF
Let’s redistribute the 192.168.1.0/24 network into OSPF as a connected network. This is okay because 192.168.1.0/24 is a Class C network. If it was a subnet then…
R2-E-O(config)#router ospf 1
R2-E-O(config-router)#redistribute connected ?
metric Metric for redistributed routes
metric-type OSPF/IS-IS exterior metric type for redistributed routes
route-map Route map reference
subnets Consider subnets for redistribution into OSPF
tag Set tag for routes redistributed into OSPF
<cr>
R2-E-O(config)#router ospf 1
R2-E-O(config-router)#redistribute connected
% Only classful networks will be redistributed
R2-E-O(config-router)#redistribute connected subnets
Redistribution into OSPF
R4-0# show ip route
<other output omitted>
E2 192.168.1.0/24 [110/20] via 172.16.0.5, 00:03:08, Serial0/0
R4-0# show ip ospf data
Type-5 AS External Link States
Link ID ADV Router Age Seq# Checksum Tag
<omitted>
192.168.1.0 192.168.1.1 193 0x80000001 0x0012B8 0
R4-0#
Summaryso far…
So far…
R2 summary:
router eigrp 1
network 172.30.0.0
auto-summary
redistribute ospf 1
default-metric 1000 33 255 1 1500
redistribute connected metric 1000 33 255 1 1500
!
router ospf 1
network 10.0.0.0 0.0.0.255 area 0
network 172.16.0.0 0.0.0.3 area 0
redistribute eigrp 1 subnets
redistribute connected
1000 33 255 1 BW=20 BW=20
OSPF learned networks are distributed into the EIGRP domain
Use the metrics for BW DLY RLY Load
Distribute any directly connected networks and use these metrics for BW DLY RLY Load
EIGRP learned networks are distributed into the OSPF domain, default metric of 20
Distribute any directly connected networks and use default metric of 20
58
Redistribution into OSPF – E2
R3-O#show ip route
O 172.17.0.0/16 [110/65] via 172.16.0.6, 00:13:41, Serial0/2
172.16.0.0/16 is variably subnetted, 4 subnets, 2 masks
C 172.16.0.4/30 is directly connected, Serial0/2
C 172.16.0.0/30 is directly connected, Serial0/1
C 172.16.1.0/24 is directly connected, FastEthernet0/0
O 172.16.2.0/24 [110/65] via 172.16.0.6, 00:13:41, Serial0/2
O E2 172.31.0.0/16 [110/20] via 172.16.0.2, 00:13:41, Serial0/1
172.30.0.0/24 is subnetted, 4 subnets
O E2 172.30.2.0 [110/20] via 172.16.0.2, 00:11:25, Serial0/1
O E2 172.30.3.0 [110/20] via 172.16.0.2, 00:11:25, Serial0/1
O E2 172.30.1.0 [110/20] via 172.16.0.2, 00:11:25, Serial0/1
O E2 172.30.4.0 [110/20] via 172.16.0.2, 00:11:25, Serial0/1
10.0.0.0/24 is subnetted, 1 subnets
O 10.0.0.0 [110/65] via 172.16.0.2, 00:13:43, Serial0/1
O E2 192.168.1.0/24 [110/20] via 172.16.0.2, 00:07:30, Serial0/1
External OSPF routes are E2 with a default cost of 20.
metric-type 2 - The cost of a type 2 route is always the external cost, irrespective of the interior cost to reach that route.
59
Redistribution into OSPF – E2
R4-0#show ip route
C 172.17.0.0/16 is directly connected, FastEthernet0/1
172.16.0.0/16 is variably subnetted, 4 subnets, 2 masks
C 172.16.0.4/30 is directly connected, Serial0/0
O 172.16.0.0/30 [110/128] via 172.16.0.5, 00:14:05, Serial0/0
O 172.16.1.0/24 [110/65] via 172.16.0.5, 00:14:05, Serial0/0
C 172.16.2.0/24 is directly connected, FastEthernet0/0
O E2 172.31.0.0/16 [110/20] via 172.16.0.5, 00:14:05, Serial0/0
172.30.0.0/24 is subnetted, 4 subnets
O E2 172.30.2.0 [110/20] via 172.16.0.5, 00:11:49, Serial0/0
O E2 172.30.3.0 [110/20] via 172.16.0.5, 00:11:49, Serial0/0
O E2 172.30.1.0 [110/20] via 172.16.0.5, 00:11:49, Serial0/0
O E2 172.30.4.0 [110/20] via 172.16.0.5, 00:11:49, Serial0/0
10.0.0.0/24 is subnetted, 1 subnets
O 10.0.0.0 [110/129] via 172.16.0.5, 00:14:07, Serial0/0
O E2 192.168.1.0/24 [110/20] via 172.16.0.5, 00:07:54, Serial0/0
External OSPF routes are E2 with a default cost of 20
60
Redistribution into OSPF modifying the metric
192.168.1.0/24 still has a cost of 20. Why? It was redistributed with the redistribute connected command without the
metric 100 parameter. <redistribute connected metric 100>
R2-E-O(config)#router ospf 1
R2-E-O(config-router)#redistribute eigrp 1 subnets metric 100
R2-E-O(config-router)#redistribute connected
R4-0#show ip route <external route>
O E2 172.31.0.0/16 [110/100] via 172.16.0.5, 00:00:04, Serial0/0
172.30.0.0/24 is subnetted, 4 subnets
O E2 172.30.2.0 [110/100] via 172.16.0.5, 00:00:05, Serial0/0
O E2 172.30.3.0 [110/100] via 172.16.0.5, 00:00:05, Serial0/0
O E2 172.30.1.0 [110/100] via 172.16.0.5, 00:00:05, Serial0/0
O E2 172.30.4.0 [110/100] via 172.16.0.5, 00:00:05, Serial0/0
O E2 192.168.1.0/24 [110/20] via 172.16.0.5, 00:12:36, Serial0/0
61
Redistribution into OSPF – E1
metric-type {1 | 2} - Defines the external metric type of 1 (E1 routes) or 2 (E2 routes).
metric-type 1 - A type 1 cost is the addition of the external cost and the internal cost used to reach that route.
metric-type 2 - The cost of a type 2 route is always the external cost, irrespective of the interior cost to reach that route.
R2-E-O(config)# router ospf 1
R2-E-O(config-router)# redistribute eigrp 1 subnets metric-type 1
R2-E-O# show run
router ospf 1
log-adjacency-changes
redistribute connected
redistribute eigrp 1 metric 100 metric-type 1 subnets
network 10.0.0.0 0.0.0.255 area 0
network 172.16.0.0 0.0.0.3 area 0
Notice that the previous metric 100 parameter is still included!
62
Redistribution into OSPF
E1 routes, seed metric of 100 plus internal cost. 192.168.1.0/24 still has a cost of 20.
It was redistributed with the redistribute connected command without the metric-type 1 parameter, E2 is the default. <redistribute connected metric 100 metric-type 1>
R3-O#show ip route
O E1 172.31.0.0/16 [110/164] via 172.16.0.2, 00:00:23, Serial0/1
172.30.0.0/24 is subnetted, 4 subnets
O E1 172.30.2.0 [110/164] via 172.16.0.2, 00:00:24, Serial0/1
O E1 172.30.3.0 [110/164] via 172.16.0.2, 00:00:24, Serial0/1
O E1 172.30.1.0 [110/164] via 172.16.0.2, 00:00:24, Serial0/1
O E1 172.30.4.0 [110/164] via 172.16.0.2, 00:00:24, Serial0/1
10.0.0.0/24 is subnetted, 1 subnets
O 10.0.0.0 [110/65] via 172.16.0.2, 00:21:45, Serial0/1
O E2 192.168.1.0/24 [110/20] via 172.16.0.2, 00:15:32, Serial0/1
More Redistribution Examples
63
Same Protocol Stack
You can only redistribute routes from routing protocols that support the same protocol stack. IPv4 to IPv4 IPv6 to IPv6
64
RIPv2 and OSPF Example
Routing tables prior to redistribution
65
The passive-interface command is configured for interface serial 0/0/2 to prevent RIPv2 from sending route advertisements out that interface.
OSPF is configured on interface serial 0/0/2.
66
X
The goal of redistribution in this network is for all routers to recognize all routes within the company.
RIPv2 is redistributed into the OSPF process, and the metric is set using the redistribute command (help prevent routing loops - later). A metric value of 300 is selected because it is a worse metric than any
belonging to a native OSPF route. Routes from OSPF process 1 are redistributed into the RIPv2 process with
a metric of 5. A value of 5 is chosen because it is higher than any metric in the RIP
network. 67
There is complete reachability; however, Routers A and C now have many more routes to keep track of than before.
They also will be affected by any topology changes in the other routing domain. 68
R 10.0.0.8/30 O E2 10.0.0.0/30
For RIPv2 on Router A, the summarization command is configured on the interface connecting to Router B, interface S0/0/0. Interface S0/0/0 advertises the summary address instead of the
individual subnets. 10.0.0.0 255.252.0.0 summarizes the four subnets on Router A
(including the 10.0.0.0/30 subnet).69
For OSPF, summarization must be configured on an area border router (ABR) or an ASBR.
Router C summarization command is configured under the OSPF process on Router C.
10.8.0.0 255.252.0.0 summarizes the four subnets on Router C. 70
Redistribution Techniques and Issues
71
Seed Metric
router ospf 1
network 172.20.0.0
redistribute rip
default-metric 501
or
redistribute rip metric 501
OSPF1 RIP
When redistributing information, the seed metric should be set to a value When redistributing information, the seed metric should be set to a value larger than the largest metric within the receiving autonomous system (aka larger than the largest metric within the receiving autonomous system (aka the largest native metric).the largest native metric).
This will help prevent suboptimal routing and routing loops.This will help prevent suboptimal routing and routing loops.
501
501
Largest metricis 500
The default seed metric value for routes that are redistributed into each IP routing protocol.
A metric of infinity tells the router that the route is unreachable and, therefore, should not be advertised. When redistributing routes into RIP, IGRP, and EIGRP, you must specify
a seed metric, or the redistributed routes will not be advertised. For OSPF, the redistributed routes have a default type 2 (E2) metric of 20,
(except for redistributed BGP routes, which have a default type 2 metric of 1)
73
One-Point Redistribution
One-point redistribution has only one router redistributing between two routing protocols.
A one-way redistribution issue that could occur… 74
R3 receives routing update information for the external route 10.0.0.0. directly from: R1 via EIGRP (AD = 170) R2 via OSPF (AD = 110)
Because the AD of OSPF (110) is lower than AD of external EIGRP routes (170), R3 selects the OSPF route. Suboptimal routing
Instead of sending packets directly from router R3 to router R1, router R3 prefers the path via router R2, resulting in suboptimal routing.
Solution: R2 should redistribute EIGRP route into OSPF with an AD of 115. We will see how to do this later.
75
R2 and R3 are both running OSPF and EIGRP
Only R2 is redistributing between OSPF en EIGRP
R1 has an External Route 10.0.0.0 that it is redistributing into its AS.
R1 is propagating this route to both R2 and R3.
10.0.0.0 via R1 has AD 170 (EX EIGRP)10.0.0.0 via R2 has AD 110 (OSPF)So, I will choose (include in my routing table) the path via R2 (OSPF)
Multipoint redistribution
Multipoint redistribution has two separate routers running both routing protocols.
Two possibilities exist: Multipoint one-way redistribution Multipoint two-way redistribution
Likely to introduce potential routing loops
76
Therefore, R2 and R3 receive routing update information for the external route 10.0.0.0: via EIGRP from router R1 and via OSPF (R2 from R3, and R3 from R2).
The AD of OSPF (110) is lower than AD of external EIGRP (170): So R2 selects the OSPF route instead of sending packets directly to R1 R2 prefers the path via router R3
Routing Loop! 77
A one-way multipoint redistribution issue.
R1 (EIGRP) is announcing routes, including the external route, to R2 and R3.
R2 and R3 are both running two routing protocols (EIGRP and OSPF) and redistributing EIGRP into OSPF.
10.0.0.0 via R1 has AD 170 (EX EIGRP)10.0.0.0 via R2 has AD 110 (OSPF)So, I will choose (include in my routing table) the path via R2 (OSPF)
10.0.0.0 via R1 has AD 170 (EX EIGRP)10.0.0.0 via R3 has AD 110 (OSPF)So, I will choose (include in my routing table) the path via R3 (OSPF)
To prevent routing loops in multipoint redistribution scenario the following recommendations should be considered: Tag routes in redistribution points and filter based on these tags when
redistributing (later) Modify the Administrative Distance of redistributed routes (later) Use default routes to avoid having to do two-way redistribution
78
10.0.0.0 via R1 has AD 170 (EX EIGRP)10.0.0.0 via R2 has AD 110 (OSPF)So, I will choose (include in my routing table) the path via R2 (OSPF)
10.0.0.0 via R1 has AD 170 (EX EIGRP)10.0.0.0 via R3 has AD 110 (OSPF)So, I will choose (include in my routing table) the path via R3 (OSPF)
The best path between R1 and R4 is via R3 But during redistribution from routing protocol B to routing protocol A, the
metric is lost Domain A doesn’t know about metrics in Domain B
R1 will send packets toward router R4 via router R2 (its best path outside its domain) Resulting in suboptimal routing.
79
A multi-way multipoint redistribution issue
Modifying Administrative Distance
80
AD
The administrative distance affects only the choice of path for identical IP routes. In other words, routes that have identical prefix and mask.
Routes with a distance of 255 are not installed in the routing table.
81
This command can be used for all protocols. There are additional options for each routing protocol.
82
Router(config-router)# distance administrative-distance [address wildcard-mask [ip-standard- list] [ip-extended-list]]
distance eigrp 80 130 Sets the administrative distance for internal EIGRP routes to 80 and for
external EIGRP routes to 130. distance 90 192.168.7.0 0.0.0.255
Sets the administrative distance to 90 for all routes learned from routers on the Class C network 192.168.7.0
distance 120 172.16.1.3 0.0.0.0 Sets the administrative distance to 120 for all routes from the router with
the address 172.16.1.3.
83
distance ospf external 100 inter-area 100 intra-area 100 Sets the administrative distance for external, inter-area, and intra-area
OSPF routes to 100 (default values are 110). distance 90 10.0.0.0 0.0.0.255, distance 110 10.11.0.0
0.0.0.255, and distance 130 10.11.12.0 0.0.0.255 Sets the administrative distance to 90, 110, and 130 respectively, for all
routes learned from routers with specific addresses Routes from a router with address 10.10.0.1 will have an AD of 90 Routes from a router with address 10.11.12.1 will have an AD of 130.
84
85
Example
R1 and R2
AD = 120
AD = 110 OSPF (AD 110) is by
default considered more believable than RIPv2 (120)
If R1 learns about network 10.3.3.0: via R2 (OSPF) Via R3 (RIPv2)
The OSPF route is used because OSPF has a lower administrative distance than RIPv2, even though the path via OSPF might be the longer (worse) path.
10.3.3.0/24
Preferred
86
Example
R1 and R2
Metric = 10,000 Metric = 10,000
Metric = 5
AD = 120
AD = 110 Note: RIPv2 routes redistributed into OSPF have an OSPF seed metric of 10,000 (higher than any other OSPF route).
This does not prevent our previous problem
Makes these routes less preferred than native OSPF routes
Protects against route feedback.
Prevents R1 from choosing R2 for OSPF routes it learns from internal OSPF routers.
The redistribute command also sets the metric type to 1 (external type 1) so that the route metrics continue to accrue.
The routers also redistribute subnet information.
10.3.3.0/24
87
Example
R1 and R2
Metric = 10,000 Metric = 10,000
Metric = 5
AD = 120
AD = 110 The OSPF routes
redistributed into RIPv2 have a RIP seed metric of five hops to also protect against route feedback.
10.3.3.0/24
R2, receives information about the RIPv2 domain routes (also called the native RIPv2 routes) from both OSPF and RIPv2.
R2 prefers the OSPF routes because OSPF has a lower administrative distance
Therefore, none of the RIPv2 routes appears in R2’s routing table. All routes are via OSPF or directly connected.
88
My best path to all RIP networks is via R1 because OSPF (110) is better than RIP (120).
Solution: Modifying the AD
You can change the administrative distance of the redistributed RIPv2 routes to ensure that the boundary routers select the native RIPv2 routes.
The distance command on R1 and R2 changes the administrative distance of the OSPF routes to the networks that match access list 64 to 125 (from 110).
Access list 64 is used to match all the native RIPv2 routes. 89
90
Metric = 10,000AD = 125
Metric = 10,000AD = 125
Metric = 5
AD = 120
AD = 110
R1 and R2 are assign an AD of 125 to routes listed in access list 64 (routes learned from OSPF).
R1 and R2 prefer the native RIPv2 routes (AD 120) over the redistributed OSPF routes (AD 125) in their routing tables.
R1 will put the 10.200.200.34 network in its routing table as a RIP route (AD 120) instead of the OSPF (AD 125) route it learned via R2.
Preferred
However, some routing information is lost with this configuration. For example, depending on the actual bandwidths, the OSPF path
might have been better for the 10.3.1.0 network; it might have made sense not to include 10.3.1.0 in the access list for R2.
91
My best path to all RIP networks is via R4 because RIP (120) is better than redistributed RIP (125).
Verifying Redistribution
The best way to verify redistribution operation is as follows: Know your network topology, particularly where redundant routes exist. Study the routing tables on a variety of routers in the internetwork using
the show ip route Perform a trace using the traceroute on some of the routes that go
across the autonomous systems to verify that the shortest path is being used for routing.
92
More on OSPF and External Routes
94
Determining the Next-hop for Type 2 External Routes- Intra-area
Review later slides for explanation
LSA 5172.30.26.0/23
Metric = 20Metric = 20
Best path
95
Determining the Next-hop for Type 2 External Routes- Interarea
172.30.26.0/23
LSA 4: I am ABR R4, I can reach
ASBR R1 and my cost to the ASBR
is 64.
LSA 4: I am ABR R3, I can reach
ASBR R1 and my cost to the ASBR
is 1. Best path
R5# show ip route
O E2 172.30.26.0/23 [110/20] via 172.16.35.3, 05:48:42, Serial0/0
Review later slides for explanation
Metric = 20
96
Comparing E1 and E2
The benefits of the different external route types apply mostly to when multiple ASBRs advertise the same subnet.
Two ASBRs, ASBR1 and ASBR2, between OSPF and another routing domain.
Goal is to always send traffic through ASBR1. Configuration:
Use E2 routes Set the metric for ASBR1's redistributed routes to a lower metric
than ASBR2. Routers ignore the internal metrics when calculating the E2 metrics,
so every router will choose ASBR1 as the better ASBR.
OSPFEIGRP ASBR1
ASBR2
E2 metric=10
E2 metric=20
97
Comparing E1 and E2
Goal is to: Balance the traffic Make each router pick the closest ASBR
Configuration: Use E1 routes
Routers closer to each ASBR choosing best routes based on the lower OSPF costs.
OSPFEIGRP ASBR1
ASBR2
E1
E1
98
Comparing E1 and E2
Note: OSPF routers will always prefers E1 routes over E2 routes for the same networks.
OSPFEIGRP ASBR1
ASBR2
E1
E2
FYI:More on OSPF and External Routes
100
Redistribution into OSPF
New Topology
EIGRP OSPF
Area 0
Area 1
101
Redistribution into OSPF
Default if no metric configuration exists Cost 1 for routes learned from BGP Cost 20 for all other route sources
default-metric cost OSPF subcommand Setting the default for all redistribute commands
metric cost parameters on the redistribute command Setting the metric for one route source
Metric transparent parameters on the redistribute command When taking routes from another OSPF process, using the metrics used by that
route source Use the route-map parameter on the redistribute command
Setting different metrics for routes learned from a single source
redistribute protocol [process-id | as-number] [metric {metric-value | transparent}] [metric-type type-value] [match {internal | external 1 | external 2 | nssa-external}] [tag tag-value] [route-map map-tag] [subnets]
102
Redistribution into OSPF
Router that performs redistribution becomes ASBR (Autonomous System Border Router).
Injects external routes into OSPF creating a Type 5 LSA for each network/subnet .
Type 5 LSA includes: LSID: the subnet number Mask: The subnet mask Advertising router: The RID of the ASBR injecting the route Metric: The metric as set by the ASBR External Metric Type: The external metric type, either 1 or 2
103
Redistribution into OSPF
ASBR floods Type 5 LSAs throughout area. If ABR is:
Normal (non-stubby) areas: Flood Type 5 LSAs into area
Stub and Totally Stubby areas: No Type 5 LSAs flooded Default route injected by ABR
LSA 5
Redistributing External Type 2 Routes
105
Redistribution into OSPF
E2 route’s metric is simply the metric in the Type 5 LSA. Default = 20 metric parameter
R4 has two routes to 172.30.26.0/23: Via R1 Via R8
To avoid loops, OSPF routers use two tiebreaker systems to allow a router to choose a best external route. Router in question resides in the same area as the ASBR (intra-area) Router in question resides in a different area (interarea) than the ASBR
LSA 5
172.30.26.0/23Metric = 20
Metric = 20
106
Determining the Next-hop for Type 2 External Routes- Intra-area
Router has multiple routes for same E2 destination network: Selects the best route based on the lowest cost to reach any ASBR(s)
that advertised the lowest E2 metric. R4: Both routes use metric 20 in this case, so the routes tie. Tiebreaker:
1. Find the advertising ASBR(s) as listed in the Type 5 LSA(s)2. Using the intra-area LSDB topology calculate the best route to reach
the ASBR(s). (This is the route that will be entered into the routing table.)
3. This determines the outgoing interface and next hop based address to to reach the ASBR
4. The route's metric is unchanged in the routing table as listed in theType 5 LSA
LSA 5172.30.26.0/23
Metric = 20Metric = 20
107
Determining the Next-hop for Type 2 External Routes- Intra-area
1. R4 looks in the Type 5 LSA, and sees RID 1.1.1.1 (R1) is the advertising ASBR.
2. R4 then looks at its area 0 LSDB entries, including the Type 1 LSA for RID 1.1.1.1, and calculates all possible area 0 routes to reach 1.1.1.1.
3. R4's best route to reach RID 1.1.1.1 happens to be through its S0/0/0 interface, to next-hop RD1 (172.16.14.1), so R4's route to 172.16.26.0/23 uses these details.
4. The route lists metric 20, as listed in the Type 5 LSA.
LSA 5172.30.26.0/23
Metric = 20Metric = 20
Best path
108
Determining the Next-hop for Type 2 External Routes- Interarea
When router is in a different area same issues remain. Different tiebreaker to reach ASBR. Calculation requires more information that previous Intra-area
example. To calculate their best route to reach the ASBR, a router in another
area: Adds the cost to reach an ABR between the areas Plus that ABR's cost to reach the ASBR
LSA 5
172.30.26.0/23
Metric = 20Metric = 20
109
Determining the Next-hop for Type 2 External Routes- Interarea
R5 has two possible routes to reach ASBR: Via R3 Via R4
Although the metric is 20, R5 will use the cost to the ABR PLUS the ABR’s cost to the ASBR to determine the best path. Via R3: 64 + 1 = 65 Via R4: 64 + 64 = 128
R5 chooses the route via R3 because it is a better path (65). The router’s process for doing this is:
1. Calculate the cost to reach the ABR, based on the area's topology database
2. Add the cost from the ABR to the ASBR, as listed in a Type 4 LSA Let’s talk about that Type 4 LSA!
172.30.26.0/23
164
6464
Best path
110
Determining the Next-hop for Type 2 External Routes- Interarea
The following slides provide additional information on LSA 4s if you are interested...
Otherwise The End
LSA 4
172.30.26.0/23
LSA 4: I am ABR R4, I can reach
ASBR R1 and my cost to the ASBR
is 64.
LSA 4: I am ABR R3, I can reach
ASBR R1 and my cost to the ASBR
is 1.
111
Determining the Next-hop for Type 2 External Routes- Interarea
Type 4 Summary ASBR LSA: RID of the ASBR RID of the ABR that created and flooded the LSA 4 ABR's cost to reach the ASBR
ABRs create Type 4 LSAs after receiving an external Type 5 LSA from an ASBR. ABR forwards a Type 5 LSA into an area ABR looks at the RID of the ASBR that created the Type 5 LSA.. ABR creates a Type 4 LSA listing that ASBR, and the cost to reach
that ASBR, flooding that LSA into the neighboring areas.
LSA 4
172.30.26.0/23
LSA 4: I am ABR R4, I can reach
ASBR R1 and my cost to the ASBR
is 64.
LSA 4: I am ABR R3, I can reach
ASBR R1 and my cost to the ASBR
is 1.
112
Determining the Next-hop for Type 2 External Routes- Interarea
ABR R3 creates and floods Type 4 Summary ASBR LSA into area 1. ASBR 1.1.1.1 (R1), ABR 3.3.3.3 (R3), and cost 1 (R3's cost to reach
ASBR). ABR R4 creates and floods Type 4 Summary ASBR LSA into area 1.
ASBR 1.1.1.1 (R1), ABR 4.4.4.4 (R4), and lists cost 64 (R4's cost to reach ASBR).
When R5 finds two routes for subnet 172.30.26.0/23, and finds both have a metric of 20
Break the tie. For each route: Add intra-area cost to reach the ABR PLUS the ABR's
cost to reach the ASBR (as listed in the Type 4 LSA). R5 determines best route is through R3 has the lower cost (65).
LSA 4
172.30.26.0/23
LSA 4: I am ABR R4, I can reach
ASBR R1 and my cost to the ASBR
is 64.
LSA 4: I am ABR R3, I can reach
ASBR R1 and my cost to the ASBR
is 1. Best path
113
Determining the Next-hop for Type 2 External Routes- Interarea
172.30.26.0/23
LSA 4: I am ABR R4, I can reach
ASBR R1 and my cost to the ASBR
is 64.
LSA 4: I am ABR R3, I can reach
ASBR R1 and my cost to the ASBR
is 1. Best path
R5# show ip route
O E2 172.30.26.0/23 [110/20] via 172.16.35.3, 05:48:42, Serial0/0
CIS 185 CCNP ROUTECh. 4 Manipulating Routing Updates
Rick Graziani
Cabrillo College
graziani@cabrillo.edu
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