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FAQ: How does OSPF imports IBGP routes from VPN-INSTANCE

Publication Date:  2014-08-25 Views:  68 Downloads:  2
Issue Description

When BGP was imported by OSPF, iBGP routes were being also imported.

The following scenario has been reproduced in eNSP for troubleshooting and analysis:

 

 

Handling Process

During troubleshooting, it was identified that RT6 was advertising 65.65.65.0 / 24 network:

 

 <RT6>dis curr conf bgp
#
bgp 65050
(...) - Output ommited

  ipv4-family vpn-instance REDE4_PRINCIPAL
  network 65.65.65.0 255.255.255.0
  import-route direct
  import-route static
  peer 1.0.0.33 as-number 65050
  peer 1.0.0.33 connect-interface LoopBack66
#

 

By having this advertisment made, RT4 was receiving this route:

 

<RT4>dis ip routing-table 65.65.65.0
Route Flags: R - relay, D - download to fib
------------------------------------------------------------------------------
Routing Table : Public
Summary Count : 1
Destination/Mask    Proto   Pre  Cost      Flags NextHop         Interface

     65.65.65.0/24  O_ASE   150  2           D   192.168.252.17  GigabitEthernet0/0/1

 

SInce RT3 and RT6 belong to the same AS, RT4 is not supposed to receive 65.65.65.0 / 24 network, because it's an IBGP route to RT3. However, a vpn-instance is configured between RT3 and RT4, what established a PE-CE relationship between these 2 routers. On this scenario, it's expected to have iBGP routes being imported to OSPF.

Root Cause
A vpn-instance is configured between RT3 and RT4, what established a PE-CE relationship between these 2 routers. On this scenario, it's expected to have iBGP routes being imported to OSPF.
Solution

In order to avoid iBGP routes of being imported by OSPF, command “vpn-instance-capability simple” was added within OSPF process 25 of RT3:

 

[RT3]ospf 25
[RT3-ospf-25]vpn-instance-capability simple

 

After configuration above was made, RT4 is no longer receiving iBGP route 65.65.65.0, but remains receiving eBGP routes like 111.111.111.0 / 24, 111.111.112.0  /24 and 111.111.113.0 / 24 that are advertised by EBGP router:

 

[RT3]ospf 25
[RT3-ospf-25]vpn-instance-capability simple

 

==================================

 <RT4>dis ip routing-table 65.65.65.0

<RT4>dis ip routing-table protocol ospf
Route Flags: R - relay, D - download to fib
------------------------------------------------------------------------------
Public routing table : OSPF
         Destinations : 6        Routes : 6       

OSPF routing table status : <Active>
         Destinations : 6        Routes : 6

Destination/Mask    Proto   Pre  Cost      Flags NextHop         Interface

       1.0.0.33/32  O_ASE   150  1           D   192.168.252.17  GigabitEthernet0/0/1
     90.90.90.0/30  O_ASE   150  1           D   192.168.252.17  GigabitEthernet0/0/1
  111.111.111.0/24  O_ASE   150  2           D   192.168.252.17  GigabitEthernet0/0/1
  111.111.112.0/24  O_ASE   150  2           D   192.168.252.17  GigabitEthernet0/0/1
  111.111.113.0/24  O_ASE   150  2           D   192.168.252.17  GigabitEthernet0/0/1
  200.200.200.0/30  O_ASE   150  1           D   192.168.252.17  GigabitEthernet0/0/1

OSPF routing table status : <Inactive>
         Destinations : 0        Routes : 0

END