0

In a PE-CE network deployment on Cisco IOS/XE devices like -


   +-------------+                                                                                                                                              +-------------+
   |             |.1  198.51.13.0/24                                                                                                      198.51.56.0/24     .6 |             |
   |  R1-CUST-A  +--------------------------+                                                                                        +--------------------------+  R6-CUST-A  |
   |             | E0/1                     |                                                                                        |                      E0/1|             |
   +-------------+              +----------------------------------------------------------------------------------------------------|-----------+              +-------------+
                                |           |                                                                                        |           |
                                |           |                                                                                        |           |
                                |       .3  | 3.3.3.3/32                            4.4.4.4/32                            5.5.5.5/32 | .5        |
                                |      +----+------------+                      +---------------+                       +------------+----+      |
                                |      |                 |.3   10.3.4.0/24    .4|               |.4     10.4.5.0/24   .5|                 |      |
                                |      |    R3-PE1       +----------------------+     R4-P      +-----------------------+    R5-PE2       |      |
                                |      |                 |E1/0              E1/0|               |E1/1               E1/1|                 |      |
                                |      +----+------------+                      +---------------+                       +------------+----+      |
                                |       .3  |E0/2                                                                               E0/2 | .5        |
                                |           |                                                                                        |           |
                                |           |                            SERVICE PROVIDER MPLS CORE NETWORK                          |           |
   +-------------+              +----------------------------------------------------------------------------------------------------|-----------+              +-------------+
   |             | E0/2                     |                                                                                        |                       .6 |             |
   |  R2-CUST-Z  +--------------------------+                                                                                        +--------------------------+  R7-CUST-Z  |
   |             |.2  198.51.23.0/24                                                                                                      198.51.57.0/24    E0/2|             |
   +-------------+                                                                                                                                              +-------------+


R3-PE1 and R5-PE2 are Provider Edge routers. R4-P is a Provider Intermediate Router. R1-CUST-A and R6-CUST-A are 'Customer A' router. R2-CUST-B and R7-CUST-B are 'Customer B' router.

In this MPLS-L3-VPN topology, to provide connectivity between customer routers, say R1-CUST-A and R6-CUST-A, we would redistribute the routes between BGP and IGP (EIGRP/OSPF) on provider edge routers (R3-PE1 and R5-PE2).

Configuration on R3-PE1 is -

BGP

router bgp 1                                                                                                                                                                                                                                                         
 bgp log-neighbor-changes                                                                                                                                                                                                                                            
 no bgp default ipv4-unicast                                                                                                                                                                                                                                         
 neighbor 5.5.5.5 remote-as 1                                                                                                                                                                                                                                        
 neighbor 5.5.5.5 update-source Loopback0                                                                                                                                                                                                                            
 !                                                                                                                                                                                                                                                                   
 address-family ipv4                                                                                                                                                                                                                                                 
 exit-address-family                                                                                                                                                                                                                                                 
 !                                                                                                                                                                                                                                                                   
 address-family vpnv4
  neighbor 5.5.5.5 activate
  neighbor 5.5.5.5 send-community extended
  neighbor 5.5.5.5 next-hop-self
 exit-address-family
 address-family ipv4 vrf CUST-A
  redistribute eigrp 65001
 exit-address-family
 !
 address-family ipv4 vrf CUST-Z
  redistribute eigrp 65026
 exit-address-family

EIGRP

router eigrp CUST-A                                                                                                                                                                                                                                                  
 !                                                                                                                                                                                                                                                                   
 address-family ipv4 unicast vrf CUST-A autonomous-system 65001                                                                                                                                                                                                      
  !
  topology base
   redistribute bgp 1 metric 1500 100 255 1 1500
  exit-af-topology
  network 198.51.13.3 0.0.0.0
 exit-address-family
router eigrp CUST-Z
 !
 address-family ipv4 unicast vrf CUST-Z autonomous-system 65026
  !
  topology base
   redistribute bgp 1 metric 1500 100 255 1 1500
  exit-af-topology
  network 198.51.23.3 0.0.0.0
 exit-address-family

Configuration on R6-PE2 is - BGP

router bgp 1                                                                                                                                                                                                                                                         
 bgp log-neighbor-changes                                                                                                                                                                                                                                            
 no bgp default ipv4-unicast                                                                                                                                                                                                                                         
 neighbor 3.3.3.3 remote-as 1
 neighbor 3.3.3.3 update-source Loopback0
 !
 address-family ipv4
 exit-address-family
 !
 address-family vpnv4
  neighbor 3.3.3.3 activate
  neighbor 3.3.3.3 send-community extended
  neighbor 3.3.3.3 next-hop-self
 exit-address-family
 !
 address-family ipv4 vrf CUST-A
  redistribute eigrp 65001
 exit-address-family
 address-family ipv4 vrf CUST-Z
  redistribute eigrp 65026
 exit-address-family

EIGRP

router eigrp CUST-Z
 !
 address-family ipv4 unicast vrf CUST-Z autonomous-system 65026
  !
  topology base
   redistribute bgp 1 metric 1500 100 255 1 1500
  exit-af-topology
  network 198.51.57.5 0.0.0.0
 exit-address-family
router eigrp CUST-A
 !
 address-family ipv4 unicast vrf CUST-A autonomous-system 65001
  !
  topology base
   redistribute bgp 1 metric 1500 100 255 1 1500
  exit-af-topology
  network 198.51.56.5 0.0.0.0
 exit-address-family

If you observer we have NOT configured bgp redistribute-internal under the BGP configuration. And I have read that the command bgp redistribute-internal is needed to be configured under BGP configuration so that BGP routes can be redistributed onto IGP protocol. However, in this scenario even without the command bgp redistribute-internal redistribution of BGP routes into IGP(EIGRP) works. How is this possible?

3
  • Is this Cisco? Juniper? Which IOS version? I found an article of Juniper that might be related: juniper.net/documentation/en_US/junose15.1/topics/reference/…
    – manish ma
    Sep 5, 2022 at 13:54
  • Sorry for not making that clear. This question is related to Cisco IOS/XE configuration.
    – Deepak
    Sep 5, 2022 at 15:52
  • Is the following assumption correct? The routes you observe being redistributed on the PE into the IGP between PE and CE, they are not prefixes your would find in the core as iBGP prefixes, but theye are per-VRF IPv4 prefixes the PE extracts from the VPNv4 prefixes learned from the remote PE (or Route Reflector). This might explain why it works: the PE is not redistributing iBGP ipv4 prefixes, but what it extracts from the given VRF's VPNv4 prefixes. Sep 5, 2022 at 19:10

1 Answer 1

1

From: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_bgp/command/irg-cr-book/bgp-a1.html?bookSearch=true#wp4270480859

Command Default In releases prior to Cisco IOS Release 15.1(2)S, 15.2(1)T, and Cisco IOS XE 3.3S, in the IPv4 VRF and IPv6 VRF address families, IBGP routes are not redistributed into IGPs

I assume you have this:

Beginning with Cisco IOS Release 15.1(2)S, 15.2(1)T, and Cisco IOS XE 3.3S, in the IPv4 VRF and IPv6 VRF address families, IBGP routes are redistributed into IGPs.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.