BGP Group Attributes: Introduction
BGP neighborhood is an non-compulsory transitive attribute. We are able to use route-maps to set communities on the BGP updates. By default the BGP communities aren’t despatched with BGP updates therefore we’ve got to particularly point out ‘send-community’ command to ship the replace with neighborhood.
Few of the well-known communities are as beneath:
- No-export: Don’t promote to EBGP friends
- No-advertise: Don’t promote this path to any peer
- Web: Promote this path to the web neighborhood, any router belongs to it.
Communities may also be utilized in BGP for the route-filtering often known as neighborhood filtering.
BGP Group Attributes
Allow us to use the topology beneath to configure and confirm the neighborhood filtering:
We’re working eBGP between R1 – R2 and R2 – R3. R3 will promote the route for 3.3.3.3 to R2 with the BGP neighborhood attribute utilized to it. First, we’ll apply neighborhood no-advertise and we’ll see as soon as R2 receives the route with neighborhood no-advertise it received’t announce the route about 3.3.3.3 to R1. Secondly we’ll use neighborhood web whereas promoting 3.3.3.3 from R3 and can be capable to see that the route of three.3.3.3 is introduced to R1.
Configuration
R3
bgp log-neighbor-changes
neighbor 9.9.23.2 remote-as 200
neighbor 9.9.23.2 send-community
neighbor 9.9.23.2 route-map Group out
route-map Group allow 10
match ip tackle ACL
set neighborhood no-advertise
R3#sh ip access-lists ACL
10 allow ip any any (2 matches)
We’re utilizing a route-map on R3 which name matches an access-list named ACL. ACL is configured to permit all site visitors. Therefore all routing updates from R3 might be matched in ACL and therefore might be set with neighborhood no-advertise.
Verification –
We see R2 has acquired route about 3.3.3.3 with neighborhood no-advertise as beneath:
R2#sh ip bgp 3.3.3.3
Paths: (1 out there, finest #1, desk default, not marketed to any peer)
Not marketed to any peer
Refresh Epoch 1
300
9.9.23.3 from 9.9.23.3 (3.3.3.3)
Origin IGP, metric 0, localpref 100, legitimate, exterior, finest
Group: no-advertise
rx pathid: 0, tx pathid: 0x0
We additionally see R2 isn’t promoting the route about 3.3.3.3 to R1 as beneath:
R2#sh ip bgp neighbors 9.9.12.1 advertised-routes
Standing codes: s suppressed, d damped, h historical past, * legitimate, > finest, i – inner,
r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,
x best-external, a additional-path, c RIB-compressed,
Origin codes: i – IGP, e – EGP, ? – incomplete
RPKI validation codes: V legitimate, I invalid, N Not discovered
Community Subsequent Hop Metric LocPrf Weight Path
*> 1.1.1.1/32 9.9.12.1 0 0 100 i
*> 2.2.2.2/32 0.0.0.0 0 32768 i
Whole variety of prefixes 2
R1#sh ip bgp
Standing codes: s suppressed, d damped, h historical past, * legitimate, > finest, i – inner,
r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,
x best-external, a additional-path, c RIB-compressed,
Origin codes: i – IGP, e – EGP, ? – incomplete
RPKI validation codes: V legitimate, I invalid, N Not discovered
Community Subsequent Hop Metric LocPrf Weight Path
*> 1.1.1.1/32 0.0.0.0 0 32768 i
*> 2.2.2.2/32 9.9.12.2 0 0 200 i
Now allow us to configure the route-map on R3 to set neighborhood to web and we will be capable to see R2 promoting the route of three.3.3.3 to R1.
Configurations –
R3:
match ip tackle ACL
set neighborhood web
Verification –
Allow us to examine on R2 now we’ll see the neighborhood as web and three.3.3.3 is introduced to R1 as beneath:
R2#sh ip bgp 3.3.3.3
Paths: (1 out there, finest #1, desk default)
Marketed to update-groups:
1
Refresh Epoch 2
300
9.9.23.3 from 9.9.23.3 (3.3.3.3)
Origin IGP, metric 0, localpref 100, legitimate, exterior, finest
Group: web
rx pathid: 0, tx pathid: 0x0
R2#sh ip bgp neighbors 9.9.12.1 advertised-routes
Standing codes: s suppressed, d damped, h historical past, * legitimate, > finest, i – inner,
r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,
x best-external, a additional-path, c RIB-compressed,
Origin codes: i – IGP, e – EGP, ? – incomplete
RPKI validation codes: V legitimate, I invalid, N Not discovered
Community Subsequent Hop Metric LocPrf Weight Path
*> 1.1.1.1/32 9.9.12.1 0 0 100 i
*> 2.2.2.2/32 0.0.0.0 0 32768 i
*> 3.3.3.3/32 9.9.23.3 0 0 300 i
Whole variety of prefixes 3
Route is acquired on R1:
R1#sh ip bgp
Standing codes: s suppressed, d damped, h historical past, * legitimate, > finest, i – inner,
r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,
x best-external, a additional-path, c RIB-compressed,
Origin codes: i – IGP, e – EGP, ? – incomplete
RPKI validation codes: V legitimate, I invalid, N Not discovered
Community Subsequent Hop Metric LocPrf Weight Path
*> 1.1.1.1/32 0.0.0.0 0 32768 i
*> 2.2.2.2/32 9.9.12.2 0 0 200 i
*> 3.3.3.3/32 9.9.12.2 0 200 300 i
Associated-
