Introduction to BGP Route Aggregation
As all of us are conscious we will promote a summarized route in BGP utilizing the “aggregate-handle“command. However there could also be few points which will come utilizing the Mixture handle command in BGP Route Aggregation.
1: If we use solely the aggregate-address command with none key phrase then the summarized route and all of the extra particular routes can be marketed.
2: If we use the summary-only key phrase then solely the summarized route can be marketed and the extra particular routes are denied from the commercial. The AS path data is nevertheless misplaced because the summarized route in it’s AS path will comprise solely the AS variety of the router on which the summarization takes place.
With a view to protect the AS path data, we will use the as-set key phrase together with summary-only key phrase which is able to protect the AS path data of the extra particular routes.
Associated- BGP Desk MAP
We’ll see these outputs shortly in our BGP Route Aggregation instance beneath.
As said in level 2 if we use the summary-only key phrase we will promote solely the abstract route and no particular routes can be marketed. However let’s suppose we wish to promote a number of particular routes together with abstract route then we might want to take the assistance of suppress-map command.
With the attribute map command, we will change the attribute of the combination route i.e. from origin of “?” to “i”.
Allow us to take the assistance of the beneath instance to grasp the above principle:
BGP Route Aggregation : Topology Diagram
Router R1 advertises beneath particular prefixes to R3.
community 172.168.0.3 masks 255.255.255.255
Associated: BGP route map
Router R2 advertises beneath particular prefixes to R3.
community 172.168.0.6 masks 255.255.255.255
Router R3 aggregates these addresses with and advertises them to R4.
R3#sh runn | sec run bgp
aggregate-address 172.168.0.0 255.255.255.248
neighbor 9.9.13.1 remote-as 100
neighbor 9.9.23.2 remote-as 200
neighbor 9.9.34.4 remote-as 400
Since we haven’t used summary-only key phrase and likewise as-set we see all particular routes are marketed and likewise below AS path on combination route we see AS 300 solely.
Routes on R4 as beneath:
We see specifics in addition to aggregated route.
AS-path comprises solely 300 therefore AS data is misplaced.[/su_note]
R4#sh ip bgp
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
*> 172.168.0.0/29 9.9.34.3 0 0 300 i
*> 172.168.0.1/32 9.9.34.3 0 300 100 i
*> 172.168.0.2/32 9.9.34.3 0 300 100 i
*> 172.168.0.3/32 9.9.34.3 0 300 100 i
*> 172.168.0.4/32 9.9.34.3 0 300 200 i
*> 172.168.0.5/32 9.9.34.3 0 300 200 i
*> 172.168.0.6/32 9.9.34.3 0 300 200 I
Now we configure Abstract-only and as-set so we obtain solely summarized route and AS-path stays preserved.
Config on R3:
R3(config-router)#$handle 172.168.0.0 255.255.255.248 summary-only as-set
Output on R4 now:
Solely summarized route is acquired and AS path data is preserved.
R4#sh ip bgp
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
*> 172.168.0.0/29 9.9.34.3 0 0 300 {100,200} I
Now allow us to say we wish to suppress solely few particular routes and permit relaxation.
We’ll enable all specifics besides 172.168.0.4 & 172.168.0.5 to be marketed together with assist of suppress-map.
Configuration :
allow 172.168.0.5
!
route-map suppress_route allow 10
match ip handle Suppress_route
!
Router bgp 300
aggregate-address 172.168.0.0 255.255.255.248 as-set summary-only suppress-map suppress_route
Output on R4:
We see all specifics together with combination handle besides 172.168.0.4 & 172.168.0.5.
*> 172.168.0.1/32 9.9.34.3 0 300 100 i
*> 172.168.0.2/32 9.9.34.3 0 300 100 i
*> 172.168.0.3/32 9.9.34.3 0 300 100 i
*> 172.168.0.6/32 9.9.34.3 0 300 200 i
Now lets us use attribute-map as nicely to alter the origin attribute on the combination route from “I” to “?”.
Config on R3 :
route-map attribute allow 10set origin incomplete
Output on R4 :
We see the origin of combination route has modified from “i” to “?”
R4#sh ip bgp
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
*> 172.168.0.0/29 9.9.34.3 0 0 300 {100,200} ?
*> 172.168.0.1/32 9.9.34.3 0 300 100 i
*> 172.168.0.2/32 9.9.34.3 0 300 100 i
*> 172.168.0.3/32 9.9.34.3 0 300 100 i
*> 172.168.0.6/32 9.9.34.3 0 300 200 I
