Hi Edward,
I have put together a relatively simple test with 4 devices, and I
definitely see a difference when "no-prepend" is used or not - below are my
initial configs and testing initially using "no-prepend", followed by not
using "no-prepend"
I hope its of some help one way or another.
Cheers,
Adam
R1
---
interface Loopback0
ip address 1.1.1.1 255.255.255.255
!
router bgp 1
no synchronization
bgp log-neighbor-changes
network 1.1.1.1 mask 255.255.255.255
neighbor 10.1.12.2 remote-as 2
no auto-summary
!
R2
---
router bgp 100
no synchronization
bgp log-neighbor-changes
neighbor 10.1.12.1 remote-as 1
neighbor 10.1.12.1 local-as 2 no-prepend
neighbor 10.1.23.3 remote-as 3
neighbor 10.1.24.4 remote-as 100
no auto-summary
!
R3
---
router bgp 3
no synchronization
bgp log-neighbor-changes
neighbor 10.1.23.2 remote-as 100
no auto-summary
!
R4
---
router bgp 100
no synchronization
bgp log-neighbor-changes
neighbor 10.1.24.2 remote-as 100
no auto-summary
!
R1>sh ip bgp | b Net
Network Next Hop Metric LocPrf Weight Path
*> 1.1.1.1/32 0.0.0.0 0 32768 i
R1>sh ip bgp nei 10.1.12.2 advertised-routes
BGP table version is 2, local router ID is 130.4.11.11
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
*> 1.1.1.1/32 0.0.0.0 0 32768 i
R2>sh ip bgp | b Net
Network Next Hop Metric LocPrf Weight Path
*> 1.1.1.1/32 10.1.12.1 0 0 1 i
R2>sh ip bgp nei 10.1.23.3 advertised-routes | b Net
Network Next Hop Metric LocPrf Weight Path
*> 1.1.1.1/32 10.1.12.1 0 0 1 i
Total number of prefixes 1
R2>sh ip bgp nei 10.1.24.4 advertised-routes | b Net
Network Next Hop Metric LocPrf Weight Path
*> 1.1.1.1/32 10.1.12.1 0 0 1 i
Total number of prefixes 1
R3>sh ip bgp | b Net
Network Next Hop Metric LocPrf Weight Path
*> 1.1.1.1/32 10.1.23.2 0 100 1 i
R4>sh ip bgp | b Net
Network Next Hop Metric LocPrf Weight Path
* i1.1.1.1/32 10.1.12.1 0 100 0 1 i
Neither R2's IBGP Peer (R4) nor it's EBGP peer (R3) see AS 2 in the AS path
-----------
Change R2 neighbor config for R1 peering so "no-prepend" isn't there
---
R2(config-router)#router bgp 100
R2(config-router)#no neighbor 10.1.12.1
R2(config-router)#neighbor 10.1.12.1 remote-as 1
R2(config-router)#neighbor 10.1.12.1 local-as 2
R2(config-router)#
00:50:56: %BGP-5-ADJCHANGE: neighbor 10.1.12.1 Down Neighbor deleted
00:50:58: %BGP-5-ADJCHANGE: neighbor 10.1.12.1 Up
R2#sh ip bgp | b Net
Network Next Hop Metric LocPrf Weight Path
*> 1.1.1.1/32 10.1.12.1 0 0 2 1 i
R2#sh ip bgp nei 10.1.23.3 advertised-routes | b Net
Network Next Hop Metric LocPrf Weight Path
*> 1.1.1.1/32 10.1.12.1 0 0 2 1 i
Total number of prefixes 1
R2#sh ip bgp nei 10.1.24.4 advertised-routes | b Net
Network Next Hop Metric LocPrf Weight Path
*> 1.1.1.1/32 10.1.12.1 0 0 2 1 i
Total number of prefixes 1
R3>sh ip bgp | b Net
Network Next Hop Metric LocPrf Weight Path
*> 1.1.1.1/32 10.1.23.2 0 100 2 1 i
R4>sh ip bgp | b Net
Network Next Hop Metric LocPrf Weight Path
* i1.1.1.1/32 10.1.12.1 0 100 0 2 1 i
R2's IBGP Peer (R4) and it's EBGP peer (R3) see AS 2 in the AS path because
R2 itself considers AS2 as part of the AS path
On Fri, Feb 24, 2012 at 10:51 AM, Bodnar, Edward
<[email protected]>wrote:
> 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]]
> *Sent:* Thursday, February 23, 2012 7:15 PM
> *To:* [email protected]; Bodnar, Edward
>
> *Cc:* [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]>;
> *To: *Adam Booth <[email protected]>;
> *Cc: *[email protected] <[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]]
> Sent: Thursday, February 23, 2012 6:11 PM
> To: Bodnar, Edward
> Cc: [email protected]
> 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]>> 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>
>
> Are you a CCNP or CCIE and looking for a job? Check out
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>
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>
>
> _______________________________________________
> 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? Check out
> www.PlatinumPlacement.com
>
> http://onlinestudylist.com/mailman/listinfo/ccie_rs****
>
> ** **
>
_______________________________________________
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? Check out
www.PlatinumPlacement.com
http://onlinestudylist.com/mailman/listinfo/ccie_rs
