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BGP Redistribute-Internal

BGP Redistribute-Internal - Concept

By default, iBGP routes do not get redistributed into the IGPs OSPF or ISIS. We need to add 'bgp redistribute-internal' under BGP router configuration to enable the BGP internal routes get redistributed in OSPF or ISIS.

BGP Redistribute-Internal

BGP Redistribute-Internal - Scenario 1

If we do not configure 'bgp redistribute-internal' command  under BGP, we will not see the route for 10.10.0.1/32 on R3.

R3#show ip route 10.10.0.1
% Subnet not in table

BGP Redistribute-Internal - Scenario 2

After adding the 'bgp redistribute-internal' command under BGP, we will see the route for 10.10.0.1/32 on R3.

R2(config-if)#router bgp 100
R2(config-router)#bgp redistribute-internal

R3#show ip route 10.10.0.1
  Routing entry for 10.10.0.1/32
  Known via "ospf 1", distance 110, metric 1, type extern 2, forward metric 1
  Last update from 10.10.23.2 on FastEthernet1/0, 00:00:03 ago
  Routing Descriptor Blocks:
  * 10.10.23.2, from 10.10.0.2, 00:00:03 ago, via FastEthernet1/0
     Route metric is 1, traffic share count is 1

Imp Note: 

Use of the bgp redistribute-internal command requires the clear ip bgp command to be issued to reset BGP connections.

R2#clear ip bgp *

Caution:

Redistributing iBGP routes into IGPs may cause routing loops to form within an autonomous system. Use this command with caution.

Or if we were running protocol ISIS between R2-R3, below is the output.

R3#show ip route 10.10.0.1
  Routing entry for 10.10.0.1/32
  Known via "isis", distance 115, metric 10, type level-2
  Redistributing via isis
  Last update from 10.10.23.2 on FastEthernet1/0, 00:00:03 ago
  Routing Descriptor Blocks:
  * 10.10.23.2, from 10.10.23.2, 00:00:03 ago, via FastEthernet1/0
     Route metric is 10, traffic share count is 1

Further Learning - Redistributing routes in BGP.

Redistributing connected routes into BGP can be done in 2 ways.

Router(config-router)#redistribute connected

or

Router(config-router)#network x.x.x.x mask x.x.x.x

Redistributing Static routes in BGP

Router(config-router)#redistribute static route-map [xyz]

Redistributing OSPF into BGP

Router(config-router)#redistribute ospf 1 route-map xyz match ?
  external       Redistribute OSPF external routes
  internal       Redistribute OSPF internal routes
  nssa-external  Redistribute OSPF NSSA external routes

Be careful while redistributing external routes back to BGP as these could cause routing loops. You can use route filtering with help of a route-map to avoid creating routing loops in network.

Redistributing ISIS into BGP

Router(config-router)#redistribute isis ?
  WORD       ISO routing area tag
  clns       Redistribution of OSI dynamic routes
  ip         Redistribution of IP dynamic routes
  level-1    IS-IS level-1 routes only
  level-1-2  IS-IS level-1 and level-2 routes
  level-2    IS-IS level-2 routes only
  metric     Metric for redistributed routes
  route-map  Route map reference
  <cr>


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