Here is the topology.
First let's get BGP configured between R1 and R2. Imagine that R1 is running an older version code where MBGP capability is not avalaible. Further assume that R2 needs to establish a MBGP session with R3 and advertise the multicast source route (192.168.1.0/24) so R3 can build the right trees and pass the RPF checks.
R1#sh run int gig1/0
Building configuration...
Current configuration : 117 bytes
!
interface GigabitEthernet1/0
description connected to r2
ip address 1.1.1.1 255.255.255.0
ip pim sparse-dense-mode
negotiation auto
end
R1#sh run | in ip route
ip route 192.168.1.0 255.255.255.0 Null0
R1#
R1#sh run | sec bgp
router bgp 1
no synchronization
bgp log-neighbor-changes
network 192.168.1.0
neighbor 1.1.1.2 remote-as 2
neighbor 1.1.1.2 description connected to r2
no auto-summary
R1#
R2#sh run int gi1/0
Building configuration...
Current configuration : 117 bytes
!
interface GigabitEthernet1/0
description connected to r1
ip address 1.1.1.2 255.255.255.0
ip pim sparse-dense-mode
negotiation auto
end
R2#sh run | sec bgp
router bgp 2
bgp log-neighbor-changes
neighbor 1.1.1.1 remote-as 1
neighbor 1.1.1.1 description connected to r1
!
address-family ipv4
neighbor 1.1.1.1 activate
neighbor 1.1.1.1 translate-update ipv4 multicast
neighbor 1.1.1.1 soft-reconfiguration inbound
no auto-summary
no synchronization
exit-address-family
!
address-family ipv4 multicast
neighbor 1.1.1.1 activate
no auto-summary
no synchronization
exit-address-family
R2#
Let's do a few show commands on R2 to verify that 192.168.1.0/24 from R1 is being installed into the mrib.
R2#sh ip route
Gateway of last resort is not set
1.0.0.0/24 is subnetted, 1 subnets
C 1.1.1.0 is directly connected, GigabitEthernet1/0
2.0.0.0/24 is subnetted, 1 subnets
C 2.2.2.0 is directly connected, GigabitEthernet2/0
!!Notice that 192.168.1.0/24 is not in the unicast routing table.
R2#show ip mbgp
BGP table version is 2, local router ID is 2.2.2.2
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 192.168.1.0 1.1.1.1 0 0 1 i
!!Notice that it is however in the mbgp table.
R2#sh ip rpf 192.168.1.0
RPF information for ? (192.168.1.0)
RPF interface: GigabitEthernet1/0
RPF neighbor: ? (1.1.1.1)
RPF route/mask: 192.168.1.0/24
RPF type: mbgp
RPF recursion count: 0
Doing distance-preferred lookups across tables
!!Notice the RPF check is stating that the route is learned via mBGP
We can now easily MBGP peer with R3 and send this route.
R2#
router bgp 2
neighbor 2.2.2.3 remote-as 3
neighbor 2.2.2.3 description connected to r3
!
address-family ipv4
no neighbor 2.2.2.3 activate
no auto-summary
no synchronization
exit-address-family
!
address-family ipv4 multicast
neighbor 2.2.2.3 activate
exit-address-family
R2#
R3 BGP and interface configs.
R3#
interface GigabitEthernet1/0
description connected to r2
ip address 2.2.2.3 255.255.255.0
ip pim sparse-dense-mode
negotiation auto
!
router bgp 3
bgp log-neighbor-changes
neighbor 2.2.2.2 remote-as 2
neighbor 2.2.2.2 description connected to r2
!
address-family ipv4
no neighbor 2.2.2.2 activate
no auto-summary
no synchronization
exit-address-family
!
address-family ipv4 multicast
neighbor 2.2.2.2 activate
no auto-summary
no synchronization
exit-address-family
!
R3#
Let's do a few show commands to verify that R3 is installing 192.168.1.0/24 into the mrib.
R3#sh ip mbgp BGP table version is 2, local router ID is 2.2.2.3 Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, r RIB-failure, S Stale Origin codes: i - IGP, e - EGP, ? - incomplete Network Next Hop Metric LocPrf Weight Path*> 192.168.1.0 2.2.2.2 0 2 1 iR3#sh ip rpf 192.168.1.0 RPF information for ? (192.168.1.0) RPF interface: GigabitEthernet1/0 RPF neighbor: ? (2.2.2.2) RPF route/mask: 192.168.1.0/24 RPF type: mbgp RPF recursion count: 0 Doing distance-preferred lookups across tables R3#sh ip mbgp summary BGP router identifier 2.2.2.3, local AS number 3 BGP table version is 2, main routing table version 2 1 network entries using 120 bytes of memory 1 path entries using 48 bytes of memory 2/1 BGP path/bestpath attribute entries using 248 bytes of memory 1 BGP AS-PATH entries using 24 bytes of memory 0 BGP route-map cache entries using 0 bytes of memory 0 BGP filter-list cache entries using 0 bytes of memory BGP using 440 total bytes of memory BGP activity 1/0 prefixes, 1/0 paths, scan interval 60 secs Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd 2.2.2.2 4 2 7 6 2 0 0 00:03:47 1 R3#
There you have it. 192.168.1.0/24 received from a BGP peer is converted into multicast NLRI and sent to R3 in a mBGP session. This should really be done in a stop-gap situation and should not be implemented in a permanent design.
Many more articles to come so stay tuned.
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Thanks for the blog. It's really great. Have a doubt . Why R2 is not learning prefix "192.168.1.0/24" in R2 unicast table where network command is there in R1?
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