Sunday, December 6, 2015

BGP advanced task #2. Fast convergence

Topology:


Requirements:

Routers R1, R2 and R3 are configured in OSPF area 0. 
Configure iBGP session between R1 and R3, use loopback addresses for peering. 
Configure R3 to advertise default route into OSPF. 
Configure routers R1 and R3 iBGP session for sub-second convergence. 

Solution:

Highlight the text below to reveal the solution.
Configure multihop BFD between iBGP peers to complete the task. 

R1:

!
bfd map ipv4  3.3.3.3/32  1.1.1.1/32 MH
bfd-template multi-hop MH
 interval min-tx 250 min-rx 250 multiplier 3
!
router bgp 123
 bgp log-neighbor-changes
 neighbor 3.3.3.3 remote-as 123
 neighbor 3.3.3.3 update-source Loopback0
 neighbor 3.3.3.3 fall-over bfd
!

R3:

!
bfd map ipv4  1.1.1.1/32  3.3.3.3/32 MH
bfd-template multi-hop MH
 interval min-tx 250 min-rx 250 multiplier 3
!
router bgp 123
 bgp log-neighbor-changes
 neighbor 3.3.3.3 remote-as 123
 neighbor 3.3.3.3 update-source Loopback0
 neighbor 3.3.3.3 fall-over bfd
!

Verification:

R1#sh bfd neighbors
IPv4 Multihop Sessions
NeighAddr[vrf]                                LD/RD         RH/RS     State
3.3.3.3                                              1/1                Up            Up

R3#show bfd neighbors

IPv4 Multihop Sessions
NeighAddr[vrf]                                LD/RD         RH/RS     State
1.1.1.1                                              1/1                Up            Up

Shutting down loopback interface on R3:

R3 log: 

*Dec  6 11:47:46.803: %BGP-5-ADJCHANGE: neighbor 1.1.1.1 Down BFD adjacency down
*Dec  6 11:47:46.803: %BGP_SESSION-5-ADJCHANGE: neighbor 1.1.1.1 IPv4 Unicast topology base removed from session  BFD adjacency down
R3(config-if)#
*Dec  6 11:47:48.209: %LINK-5-CHANGED: Interface Loopback0, changed state to administratively down
*Dec  6 11:47:49.218: %LINEPROTO-5-UPDOWN: Line protocol on Interface Loopback0, changed state to down
R3(config-if)#^Z
R3#
*Dec  6 11:47:52.990: %SYS-5-CONFIG_I: Configured from console by console

R1 log: 

R1#
*Dec  6 11:47:46.813: %BGP-5-ADJCHANGE: neighbor 3.3.3.3 Down BFD adjacency down
*Dec  6 11:47:46.813: %BGP_SESSION-5-ADJCHANGE: neighbor 3.3.3.3 IPv4 Unicast topology base removed from session  BFD adjacency down

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