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10-1 redistribute protocol

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Syntax Description:

  • protocol— Routes learned via protocol will be redistributed into BGP.

Purpose: To redistribute routes into BGP that have been learned via a routing protocol other than BGP. The metric of the non-BGP-learned routes is transferred to the metric or multi-exit discriminator (MED) of the new BGP route. Routes can be redistributed from connected, dvmrp, egp, eigrp, igrp, isis, iso-igrp, mobile, odr, ospf, rip, and static.

Cisco IOS Software Release: 10.0

Configuration Example: Redistributing Connected, Static, and EIGRP Learned Routes into BGP

In Figure 10-1, Router C is advertising 172.16.2.0/24 and 172.16.3.0/24 to Router B via EIGRP. Routers A and B have an EBGP relationship. This example redistributes EIGRP and static into BGP on Router B and redistributes connected on Router A.

Figure 10-1. Redistributing Routes into BGP

image 

Router A

interface loopback 0

 ip address 172.16.0.1 255.255.255.0

!

interface loopback 1

 ip address 172.16.1.1 255.255.255.0

!

router bgp 1

 network 172.17.1.0 mask 255.255.255.0

 neighbor 172.17.1.1 remote-as 2

___________________________________________________________________________

Router B

router eigrp 1

 network 10.0.0.0

 network 172.17.0.0

 no auto-summary

!

router bgp 2

 network 10.1.0.0 mask 255.255.255.252

 network 172.17.1.0 mask 255.255.255.0

 neighbor 172.17.1.2 remote-as 1

!

ip route 172.16.4.0 255.255.255.0 s2/0

___________________________________________________________________________

Router C

interface loopback 0

 ip address 172.16.2.1 255.255.255.0

!

interface loopback 1

 ip address 172.16.3.1 255.255.255.0

!

router eigrp 1

 network 172.16.0.0

 network 10.0.0.0

 no auto-summary

Before proceeding with the redistribution of routes into BGP, inspect the IP and BGP routing tables on Routers A and B. Router B should be learning routes 172.16.2.0/24 and 172.16.3.0/24 from Router C via EIGRP. Because you are not redistributing routes on Router B, Router A should not be learning about the 172.16.2.0/24 or 172.16.3.0/24 routes.

rtrB#show ip route

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 2

       E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP

       i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area

       * - candidate default, U - per-user static route, o - ODR

       P - periodic downloaded static route



Gateway of last resort is not set



     172.17.0.0/24 is subnetted, 1 subnets

C       172.17.1.0 is directly connected, Ethernet0/0

     172.16.0.0/24 is subnetted, 3 subnets

S       172.16.4.0 is directly connected, Serial2/0

D       172.16.2.0 [90/1889792] via 10.1.1.2, 00:26:32, Serial2/0

D       172.16.3.0 [90/1889792] via 10.1.1.2, 00:26:32, Serial2/0

     10.0.0.0/30 is subnetted, 1 subnets

C       10.1.1.0 is directly connected, Serial2/0



rtrB#show ip bgp

BGP table version is 3, local router ID is 172.17.1.1

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal

Origin codes: i - IGP, e - EGP, ? - incomplete



   Network          Next Hop            Metric LocPrf Weight Path

*> 10.1.1.0/30      0.0.0.0                  0         32768 i

*  172.17.1.0/24    172.17.1.2               0             0 1 i

*>                  0.0.0.0                  0         32768 i

___________________________________________________________________________

rtrA#show ip route

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 2

       E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP

       i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area

       * - candidate default, U - per-user static route, o - ODR

       P - periodic downloaded static route



Gateway of last resort is not set



     172.17.0.0/24 is subnetted, 1 subnets

C       172.17.1.0 is directly connected, FastEthernet0

     172.16.0.0/24 is subnetted, 2 subnets

C       172.16.0.0 is directly connected, Loopback0

C       172.16.1.0 is directly connected, Loopback1

     10.0.0.0/30 is subnetted, 1 subnets

B       10.1.1.0 [20/0] via 172.17.1.1, 00:25:38



rtrA#show ip bgp

BGP table version is 4, local router ID is 172.16.1.1

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal

Origin codes: i - IGP, e - EGP, ? - incomplete



   Network          Next Hop            Metric LocPrf Weight Path

*> 10.1.1.0/30      172.17.1.1               0             0 2 i

*> 172.17.1.0/24    0.0.0.0                  0         32768 i

*                   172.17.1.1               0             0 2 i

Notice that the metric for the EIGRP learned routes on Router B is 1889792. Because the form of the redistribute command that you will use does not contain a metric, the router uses the EIGRP metric for the BGP MED for the redistributed EIGRP routes. Now modify the BGP configuration on Router B to enable the redistribution of the EIGRP and static routes into BGP. Also modify the configuration on Router A to enable the redistribution of connected routes:

Router A

router bgp 1

 network 172.17.1.0 mask 255.255.255.0

 redistribute connected

 neighbor 172.17.1.1 remote-as 2

___________________________________________________________________________

Router B

router bgp 1

 network 10.1.0.0 mask 255.255.255.0

 network 172.17.1.0 mask 255.255.255.0

 redistribute static

 redistribute eigrp 1

 neighbor 172.17.1.2 remote-as 2

Verification

Verify that the connected routes are being redistributed in BGP on Router A and that the static and EIGRP routes are being redistributed on Router B:

rtrA#show ip bgp

BGP table version is 8, local router ID is 172.17.1.1

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal

Origin codes: i - IGP, e - EGP, ? - incomplete



   Network          Next Hop            Metric LocPrf Weight Path

*> 10.0.0.0         0.0.0.0                  0         32768 ?

*> 10.1.1.0/30      0.0.0.0                  0         32768 i

*> 172.16.0.0       0.0.0.0                  0         32768 ?

*                   172.17.1.2               0             0 1 ?

*> 172.17.0.0       172.17.1.2               0             0 1 ?

*> 172.17.1.0/24    0.0.0.0                  0         32768 i

*                   172.17.1.2               0             0 1 i

__________________________________________________________________________

rtrB#show ip bgp

BGP table version is 19, local router ID is 172.16.1.1

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal

Origin codes: i - IGP, e - EGP, ? - incomplete



   Network          Next Hop            Metric LocPrf Weight Path

*> 10.0.0.0         172.17.1.1               0             0 2 ?

*> 10.1.1.0/30      172.17.1.1               0             0 2 i

*  172.16.0.0       172.17.1.1               0             0 2 ?

*>                  0.0.0.0                  0         32768 ?

*> 172.17.0.0       0.0.0.0                  0         32768 ?

*  172.17.1.0/24    172.17.1.1               0             0 2 i

*>                  0.0.0.0                  0         32768 i

Why is the mask for the 172.16.x.x routes /16 (the entire Class B address 172.16.x.x)? By default, BGP summarizes redistributed routes on a classful boundary (see Chapter 2, "Auto-Summary"). Routers A and B now indicate that they can reach the entire Class B address block 172.16.x.x. Typically, this is not the behavior you want. When redistributing routes into BGP, it is a good idea to turn off auto-summarization. Modify the BGP configuration on Routers A and B to do this. Notice that Router A also summarizes the 10.0.0.0 and 172.17.0.0 networks because they are also directly connected.

Router A

router bgp 1

 network 172.17.1.0 mask 255.255.255.0

 redistribute connected 5

 neighbor 172.17.1.1 remote-as 2

 no auto-summary

___________________________________________________________________________

Router B

router bgp 1

 network 10.1.0.0 mask 255.255.255.252

 network 172.17.1.0 mask 255.255.255.0

 redistribute static 10

 redistribute eigrp 15

 neighbor 172.17.1.2 remote-as 2

 no auto-summary

Reinspect the BGP tables on Routers A and B:

rtrA#show ip bgp

BGP table version is 8, local router ID is 172.16.1.1

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal

Origin codes: i - IGP, e - EGP, ? - incomplete



   Network          Next Hop            Metric LocPrf Weight Path

*> 10.1.1.0/30      172.17.1.1               0             0 2 i

*> 172.16.0.0/24    0.0.0.0                  0         32768 ?

*> 172.16.1.0/24    0.0.0.0                  0         32768 ?

*> 172.16.2.0/24    172.17.1.1         1889792             0 2 ?

*> 172.16.3.0/24    172.17.1.1         1889792             0 2 ?

*> 172.16.4.0/24    172.17.1.1               0             0 2 ?

*  172.17.1.0/24    172.17.1.1               0             0 2 i

*>                  0.0.0.0                  0         32768 i

___________________________________________________________________________

rtrB#show ip bgp

BGP table version is 19, local router ID is 172.17.1.1

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal

Origin codes: i - IGP, e - EGP, ? - incomplete



   Network          Next Hop            Metric LocPrf Weight Path

*> 10.1.1.0/30      0.0.0.0                  0         32768 i

*> 172.16.0.0/24    172.17.1.2               0             0 1 ?

*> 172.16.1.0/24    172.17.1.2               0             0 1 ?

*> 172.16.2.0/24    10.1.1.2           1889792         32768 ?

*> 172.16.3.0/24    10.1.1.2           1889792         32768 ?

*> 172.16.4.0/24    0.0.0.0                  0         32768 ?

*  172.17.1.0/24    172.17.1.2               0             0 1 i

*>                  0.0.0.0                  0         32768 i

The metric or MED value for the redistributed EIGRP routes is equal to the EIGRP metric for those routes. The metric or MED value for the redistributed connected and static routes is 0.

Troubleshooting

Step 1. Verify that the BGP neighbors are in the Established state using the show ip bgp neighbors command.

If the neighbor relationship is not in the Established state, see section 8-23.

Step 2. Verify that the protocol you are redistributing routes from is active on the router.
Step 3. When redistributing from a protocol that requires a process ID, verify that you are using the proper process ID in the redistribute command.
Step 4. Use the no auto-summary command under router BGP when redistributing routes into BGP.


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