Same topology as my previous blogtorial BGP Communities No-Advertise
Complete configs can be downloaded here.
The purpose of the no-export community is to mark a destination so that the peer does not advertise it outside of its own AS. If confederations are used then the route should stay within the confederation meaning the routes can pass to sub-confederations.
The purpose of the no-export community is to mark a destination so that the peer does not advertise it outside of its own AS. If confederations are used then the route should stay within the confederation meaning the routes can pass to sub-confederations.
Again if you need to look at the interface / BGP configuration check out my previous post. The only thing we are going to modify here is the route-map on R1 so that the loopback (11.11.11.11/32) can be advertised to R2 with no-export community.
!
hostname R1
!
ip access-list standard acl-loopback-advertise-with-community
remark match loopback
permit 11.11.11.11
!
route-map loopback-advertise-with-comunity permit 10
match ip address acl-loopback-advertise-with-community
set community no-export
!
router bgp 1
no synchronization
bgp log-neighbor-changes
network 11.11.11.11 mask 255.255.255.255
neighbor 1.1.1.2 remote-as 2
neighbor 1.1.1.2 send-community both
neighbor 1.1.1.2 route-map loopback-advertise-with-comunity out
no auto-summary
!
!
hostname R2
!
router bgp 2
no synchronization
bgp log-neighbor-changes
neighbor 1.1.1.1 remote-as 1
neighbor 2.2.2.3 remote-as 2
!!next-hop-self is needed for the iBGP peer to R3. If not, R3 would see the next hop as 1.1.1.1
and since it does not have a route to 1.1.1.1 the loopback route will not be installed in the
routing table.!!
neighbor 2.2.2.3 next-hop-self
neighbor 4.4.4.4 remote-as 4
no auto-summary
!
Let's make sure that 11.11.11.11/32 from R1 is being advertised by R2 to R3 (iBGP) and not R4 (eBGP).
R2 advertises the route 11.11.11.11/32 to R3 since they are iBGP neighbors. |
R3 does have the route in its routing table. |
Many more articles to come so stay tuned.
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