Task 5.5 - Alternative Solution

Hi

In the solution to this Task, it has R1 and SW1 filtering off all routes originated in AS 254 when advertising to AS 100 so the only link used is the FR link between R2 and R4.

The solution I came up with used the community group "No-Export" so AS 200 learns of all routes originated in AS 254 but doesn't advertised them to their respective AS 100 eBGP neighbors. The solution used was:

R2
ip as-path access-list 1 permit _254$
!

route-map TASK5.5 permit 10
match as-path 1
set community no-export
!
route-map TASK5.5 permit 20
!
router bgp 200
neighbor 129.1.23.3 send-community
neighbor 129.1.23.3 route-map TASK5.5 out

On R3 and R1, configure the "neighbor x.x.x.x send-community" to their respective iBGP neighbors (R3->R1->SW1)

So R1 and R3 won't advertise the prefixes learnt in AS 254 via eBGP:

R1

Rack1R1#show ip bgp 205.90.31.0 | begin Adver
Advertised to update-groups:
2
254
129.1.23.2 (metric 2681856) from 129.1.13.3 (150.1.3.3)
Origin incomplete, metric 0, localpref 100, valid, internal, best
Community: no-export
Originator: 150.1.2.2, Cluster list: 150.1.3.3

SW1

Rack1SW1#show ip bgp 205.90.31.0
BGP routing table entry for 205.90.31.0/24, version 19
Paths: (1 available, best #1, table Default-IP-Routing-Table, not advertised to EBGP peer)
Not advertised to any peer

254
129.1.23.2 (metric 2682112) from 129.1.17.1 (150.1.1.1)
Origin incomplete, metric 0, localpref 100, valid, internal, best
Community: no-export
Originator: 150.1.2.2, Cluster list: 150.1.1.1, 150.1.3.3

On R4, it only sees the _254$ routes from R2

Rack1R4#show ip bgp quote-regexp _254$
BGP table version is 67, local router ID is 150.1.4.4
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
*> 205.90.31.0 129.1.124.2 0 200 254 ?
*> 220.20.3.0 129.1.124.2 0 200 254 ?
*> 222.22.2.0 129.1.124.2 0 200 254 ?
Rack1R4#

Would this be an acceptable solution as the requirements have been met??

Comments


  • router bgp 200
    neighbor 129.1.23.3 send-community both
    neighbor 129.1.23.3 route-map TO-R3 out
    neighbor 192.10.1.254 route-map BB2-IN in
    !
    ip bgp-community new-format
    !
    ip community-list 22 permit 22:22
    !
    route-map BB2-IN permit 10
    set community 22:22
    route-map TO-R3 permit 10
    match community 22
    set community no-export
    route-map TO-R3 permit 1000
  • Looks solid to me. Neater actually since the config is only on one box instead of two. Come to think of it, I'm going to tell everyone *I* thought of that.
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