Let me see if I can help. You almost have it except, you will not be blocking anything. You will be removing the ASN 100 from the AS PATH that would otherwise have ASN 100 in it from routes coming inbound from R2 (same for R3).
Say R2 is advertising network 11.11.11.11 to R1. R1 would have the AS PATH of 100 200 for this advertisement. With the no-prepend the AS PATH would just be 200. So, despite how it seems, the no-prepend keyword effects the AS PATH on inbound advertisements. Like others have said, use replace-as to effect the AS PATH of outbound advertisement. DEREK -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Bodnar, Edward Sent: Friday, February 24, 2012 7:01 AM To: Oluwagbenga Oyebande Cc: [email protected] Subject: Re: [OSL | CCIE_RS] BGP local-as no-pepend I see AS 101 on R3 also. I don't see why R3 should be different then R2. If I am reading what you are saying correct then I would be blocking AS 101 from coming to R1 inbound. R1 is AS 101 so I would be blocking AS 101 inbound from R2 that does not have AS 101 in it's path? Is this what you're saying. I set EX Router bgp 100 Neigh 2.2.2.2 remote-as 200 neigh 2.2.2.2 local-as 10 no-prepend ( I will block AS 100 from coming into R1 from R2 ? If so the command makes no sense, I do not have AS 100 coming in inbound ) . From: [email protected] [mailto:[email protected]] On Behalf Of Oluwagbenga Oyebande Sent: Friday, February 24, 2012 7:22 AM To: Bodnar, Edward Cc: ar; Steve Storniak; [email protected]; [email protected] Subject: Re: [OSL | CCIE_RS] BGP local-as no-pepend The no-prepend keyword gives your "other bgp neighbors" (that are not a party to the AS migration) time to fix bgp routing policies that would be adversely affected by the default crude action of prepending an unknown AS in the path of routes received from you local-as peer (who of course is a party to the AS migration). It's like extending the migration window facilitated by the local-as command to the "other bgp neighbors". The keyword to remember when dealing with no-prepend is "other bgp neighbors". On 24 February 2012 13:04, Oluwagbenga Oyebande <[email protected]<mailto:[email protected]>> wrote: Removing AS101 from the path of routes advertised to R2's is a job for replace-as keyword. What no-prepend keyword will do in your config is to remove your local-as (100) that R1 would otherwise prepend to adverts received from R2 before sending them out. You will not see AS 100 in the path of adverts R1 makes to R3(3.3.3.3). Check on R3 whether local-as worked, not on R1. On 24 February 2012 12:48, Bodnar, Edward <[email protected]<mailto:[email protected]>> wrote: Let me know if you see anything off on the config. Still not sure why this is not working. I was expecting to see R2 not having AS 101 in it's path. R1 router bgp 101 no synchronization bgp router-id 1.1.1.1 bgp log-neighbor-changes network 33.33.33.0 mask 255.255.255.0 network 55.55.55.0 mask 255.255.255.0 network 55.55.56.0 mask 255.255.255.0 network 55.55.57.0 mask 255.255.255.0 network 55.55.58.0 mask 255.255.255.0 network 55.55.59.0 mask 255.255.255.0 network 100.100.10.0 mask 255.255.255.0 aggregate-address 55.55.0.0 255.255.192.0 summary-only neighbor 2.2.2.2 remote-as 200 neighbor 2.2.2.2 local-as 100 no-prepend neighbor 2.2.2.2 ebgp-multihop 255 neighbor 2.2.2.2 update-source Loopback0 neighbor 2.2.2.2 send-community neighbor 2.2.2.2 route-map CoM out neighbor 3.3.3.3 remote-as 300 neighbor 3.3.3.3 local-as 100 no-prepend neighbor 3.3.3.3 ebgp-multihop 255 neighbor 3.3.3.3 update-source Loopback0 R2 router bgp 200 no synchronization bgp log-neighbor-changes bgp inject-map NEW exist-map NEED-UM neighbor 1.1.1.1 remote-as 100 neighbor 1.1.1.1 ebgp-multihop 255 neighbor 1.1.1.1 update-source Loopback0 neighbor 5.5.5.5 remote-as 200 neighbor 5.5.5.5 update-source Loopback0 neighbor 5.5.5.5 send-community neighbor 5.5.5.5 default-originate no auto-summary R2#sh ip bgp BGP table version is 65, 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 *> 33.33.33.0/24<http://33.33.33.0/24> 1.1.1.1 0 0 100 101 i *> 55.55.0.0/18<http://55.55.0.0/18> 1.1.1.1 0 0 100 101 i *> 55.55.56.0/24<http://55.55.56.0/24> 1.1.1.1 0 ? *> 100.100.10.0/24<http://100.100.10.0/24> 1.1.1.1 0 0 100 101 i From: [email protected]<mailto:[email protected]> [mailto:[email protected]<mailto:[email protected]>] On Behalf Of Oluwagbenga Oyebande Sent: Thursday, February 23, 2012 10:12 PM To: ar Cc: Bodnar, Edward; Steve Storniak; [email protected]<mailto:[email protected]>; [email protected]<mailto:[email protected]> Subject: Re: [OSL | CCIE_RS] BGP local-as no-pepend It actually works as Adams has proved. The problem is that people wrongly expect it to work on adverts to the local-as peer. It works on adverts to other bgp peers. It strips off the local-as that was prepended to routes received from the local-as peer. On 24 February 2012 02:53, ar <[email protected]<mailto:[email protected]>> wrote: Hi. This local-as no prepend feature is not working based on my experience. What platforms are you using? ________________________________ From: "Bodnar, Edward" <[email protected]<mailto:[email protected]>> To: Steve Storniak <[email protected]<mailto:[email protected]>>; "[email protected]<mailto:[email protected]>" <[email protected]<mailto:[email protected]>> Cc: "[email protected]<mailto:[email protected]>" <[email protected]<mailto:[email protected]>> Sent: Thursday, February 23, 2012 4:51 PM Subject: Re: [OSL | CCIE_RS] BGP local-as no-pepend I will grab and post my config tomorrow. Either I am not understanding this command or I am not configuring it right. It's a fairly simple command so I can't see the latter but I will post my config. From: Steve Storniak [mailto:[email protected]<mailto:[email protected]>] Sent: Thursday, February 23, 2012 7:15 PM To: [email protected]<mailto:[email protected]>; Bodnar, Edward Cc: [email protected]<mailto:[email protected]> Subject: Re: [OSL | CCIE_RS] BGP local-as no-pepend Per RFC "no-prepend" instructs the node to not add the local as to prefixes received from other eBGP peers. "Replace-as" removes the local as in the as-path sent to eBGP peers. Am O wrong? Steve ________________________________ From: Bodnar, Edward <[email protected]<mailto:[email protected]>>; To: Adam Booth <[email protected]<mailto:[email protected]>>; Cc: [email protected]<mailto:[email protected]> <[email protected]<mailto:[email protected]>>; Subject: Re: [OSL | CCIE_RS] BGP local-as no-pepend Sent: Thu, Feb 23, 2012 11:27:59 PM I 100% agree. Just not sure what the local-as no-prepend does. From: Adam Booth [mailto:[email protected]<mailto:[email protected]><javascript:return>] Sent: Thursday, February 23, 2012 6:11 PM To: Bodnar, Edward Cc: [email protected]<mailto:[email protected]><javascript:return> Subject: Re: [OSL | CCIE_RS] BGP local-as no-pepend Hi Edward. If also you include "replace-as" in the neighbor statement, AS 100 should be hidden. Cheers, Adam On Fri, Feb 24, 2012 at 6:48 AM, Bodnar, Edward <[email protected]<mailto:[email protected]><javascript:return><mailto:[email protected]<mailto:[email protected]><javascript:return>>> wrote: Not sure what this command is suppose to do . I set it and it does not filter any AS's Router bgp 100 Neigh 2.2.2.2 Local-as 10 no-prepend The router on the other side will still see AS 100 and AS10 in its path. _______________________________________________ For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com<http://www.ipexpert.com><http://www.ipexpert.com> Are you a CCNP or CCIE and looking for a job? Check out www.PlatinumPlacement.com<http://www.PlatinumPlacement.com><http://www.PlatinumPlacement.com> http://onlinestudylist.com/mailman/listinfo/ccie_rs _______________________________________________ For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com<http://www.ipexpert.com> Are you a CCNP or CCIE and looking for a job? Check out www.PlatinumPlacement.com<http://www.PlatinumPlacement.com> http://onlinestudylist.com/mailman/listinfo/ccie_rs _______________________________________________ For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com<http://www.ipexpert.com> Are you a CCNP or CCIE and looking for a job? Check out www.PlatinumPlacement.com<http://www.PlatinumPlacement.com> http://onlinestudylist.com/mailman/listinfo/ccie_rs _______________________________________________ For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com<http://www.ipexpert.com> Are you a CCNP or CCIE and looking for a job? Check out www.PlatinumPlacement.com<http://www.PlatinumPlacement.com> http://onlinestudylist.com/mailman/listinfo/ccie_rs -- -- Olugbenga Oyebande MD, DAIT 234-803-302-5287 http://www.dait-ng.com<http://www.dait-ng.com/> Cisco Networks, Network Security & Quality of Service DAIT Linux Enterprise Network Servers, Web Portal Projects Broadband Internet Deployment & ISP Consultancy -- -- Olugbenga Oyebande MD, DAIT 234-803-302-5287 http://www.dait-ng.com<http://www.dait-ng.com/> Cisco Networks, Network Security & Quality of Service DAIT Linux Enterprise Network Servers, Web Portal Projects Broadband Internet Deployment & ISP Consultancy -- -- Olugbenga Oyebande MD, DAIT 234-803-302-5287 http://www.dait-ng.com<http://www.dait-ng.com/> Cisco Networks, Network Security & Quality of Service DAIT Linux Enterprise Network Servers, Web Portal Projects Broadband Internet Deployment & ISP Consultancy _______________________________________________ For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com Are you a CCNP or CCIE and looking for a job? 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