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?