RE: BGP AS-PATH PREPEND

Sure Jeff that makes sense.

There was a nagging in my mind saying if a route map matches something on
one line and does nothing with it, then it will be excluded from the next
map statement in the rmap. :)

Sam.
On 8 Jan 2014 17:43, "Jeff Lodwick" <jeff_at_tydesystems.com> wrote:

> Sam,
> I don't think the problem is with the way the route-map and ACL are
> configured. I've configured it the way Cisco Fanatic configured it
> multiple
> times and this is the correct way to configure it. The way you are
> recommending is accomplishing the same results as the way Cisco Fanatic is
> configuring it, but the way Cisco Fanatic is configuring it is actually a
> more common way of configuring this. I generally don't recommend denying
> in
> an ACL or prefix-list, then permitting in the route-map because I've seen
> problems with this working correctly.
>
> Jeffrey Lodwick - CCIE 15671 R&S
> Senior Data Engineer / Owner
> Jeff_at_tydesystems.com
> Office: 303-346-9988
> Mobile: 303-919-1366
>
> www.tydesystems.com
>
>
> -----Original Message-----
> From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of
> Sam
> Bibby
> Sent: Wednesday, January 08, 2014 10:15 AM
> To: Cisco Fanatic
> Cc: Tony Singh; ccielab_at_groupstudy.com
> Subject: Re: BGP AS-PATH PREPEND
>
> Oh I see, so you want to pre-pend everything except that one route, well
> that possible, Try then changing the things so as to deny the route you
> don't want to pre-pend & permit everything else
>
> !
> router bgp 65500
> neighbor 10.255.0.26 route-map AS_CHANGE out !
> route-map AS_CHANGE permit 10
> match ip address prefix OVER_L2
> set as-path prepend 65500 65500 65500
> !
> ip prefix-list AS_CHANGE deny
> ip access-list extended OVER_L2 deny X.X.X..X/XX *!!!the orute you
> dont want to prepend*
> ip access-list extended OVER_L2 permit 0.0.0.0/0 le 32 *!!!Permit
> everything else to get prepended*
>
>
>
> Without a full understanding of the topology I have to make some
> assumptions
> & I am trying to understand your issue a bit better,
>
> *1)Because I only want 10.100.60.11 (source) to go over Layer 2 (a name)
> 10.20.80.11 (destination). The rest should all be prepended. *
>
> *I don't see a route to 10.20.80.11 in the bgp output you send over:* R1#sh
> ip bgp
> > BGP table version is 196, local router ID is 10.255.255.2 Status
> > codes: s suppressed, d damped, h history, * valid, > best, i -
> > internal,
> > r RIB-failure, S Stale, m multipath, b backup-path, x
> > best-external, f RT-Filter Origin codes: i - IGP, e - EGP, ? -
> > incomplete
> > Network Next Hop Metric LocPrf Weight Path
> > *> 10.3.0.0/16 0.0.0.0 0 32768 ?
> > *> 10.7.0.0/24 0.0.0.0 0 32768 ?
> > *> 10.11.0.0/24 0.0.0.0 0 32768 ?
> > *> 10.13.0.0/16 10.255.255.1 0 1 65501 ?
> > * 10.255.0.26 0 0 65501 65501
> 65501 65501 ?
> > *> 10.16.0.0/24 0.0.0.0 0 32768 ?
> > *> 10.20.0.0/24 10.255.255.1 0 1 65501 ?
> > * 10.255.0.26 28416 0 65501 65501 65501 65501 ?
>
>
> \Sam
>
>
>
> On Wed, Jan 8, 2014 at 4:53 PM, Cisco Fanatic
> <ebay_products_at_hotmail.com>wrote:
>
> > Because I only want 10.100.60.11 (source) to go over Layer 2 (a name)
> > 10.20.80.11 (destination). The rest should all be prepended.
> >
> > ip access-list extended OVER_L2
> > permit ip host 10.100.60.11 host 10.20.80.11
> >
> > With your suggestion all the traffic will be prepended (longer AS
> > path) and it will not be the best route.
> >
> >
> > ------------------------------
> > Date: Wed, 8 Jan 2014 16:36:40 +0000
> >
> > Subject: Re: BGP AS-PATH PREPEND
> > From: sammybibs_at_gmail.com
> > To: ebay_products_at_hotmail.com
> > CC: mothafungla_at_gmail.com; ccielab_at_groupstudy.com
> >
> >
> > I'm pretty sure the route map is wrong here,
> >
> > *!!!Yours*
> > !
> > *!You match the ACL but don't do anything with it.* !
> > route-map AS_CHANGE permit 10
> > match ip address OVER_L2
> > !
> > *! You then pre-pend everything via the match all in the next
> > statement* !
> > route-map AS_CHANGE permit 20
> > set as-path prepend 65500 65500 65500 !
> >
> > *!!!Suggestion*
> > !
> > !You match the ACL but don't do anything with it.
> > !
> > route-map AS_CHANGE permit 10
> > match ip address OVER_L2
> > set as-path prepend 65500 65500 65500 !
> >
> > \Sam
> >
> >
> > On Wed, Jan 8, 2014 at 4:31 PM, Cisco Fanatic
> <ebay_products_at_hotmail.com>wrote:
> >
> > Sorry, cut-paste issue, too many notepad open.
> >
> > R1
> > ++
> >
> > !
> > router bgp 65500
> > neighbor 10.255.0.26 route-map AS_CHANGE out !
> > route-map AS_CHANGE permit 10
> > match ip address OVER_L2
> > !
> > route-map AS_CHANGE permit 20
> > set as-path prepend 65500 65500 65500 !
> > ip access-list extended OVER_L2
> > permit ip host 10.100.60.11 host 10.20.80.11 !
> >
> > It is still going over the other connection...
> >
> > R1#traceroute 10.20.80.11
> > Type escape sequence to abort.
> > Tracing the route to 10.20.80.11
> > VRF info: (vrf in name/id, vrf out name/id)
> > 1 10.255.255.1 4 msec 0 msec 4 msec
> > 2 10.255.255.22 [AS 1] 4 msec 0 msec 4 msec
> > 3 10.13.0.253 [AS 65501] 4 msec 4 msec 0 msec
> >
> >
> >
> >
> >
> >
> > > Subject: Re: BGP AS-PATH PREPEND
> > > From: mothafungla_at_gmail.com
> > > Date: Wed, 8 Jan 2014 15:59:21 +0000
> > > CC: ccielab_at_groupstudy.com
> > > To: ebay_products_at_hotmail.com
> > >
> > > Where's your match extended ACL in route-map condition ?
> > >
> > > --
> > > BR
> > >
> > > Tony
> > >
> > > > On 8 Jan 2014, at 15:47, Cisco Fanatic <ebay_products_at_hotmail.com>
> > wrote:
> > > >
> > > > I understand how AS-PATH PREPEND works, but I am not able to make
> > > > it
> > work
> > if I
> > > > need to manipulate traffic paths only from a specific source to a
> > specific
> > > > destination.
> > > >
> > > > R1
> > > > ++
> > > >
> > > > !
> > > > router bgp 65500
> > > >
> > > > neighbor 10.255.0.26 route-map AS_CHANGE out
> > > >
> > > > !
> > > > route-map AS_CHANGE permit 10
> > > >
> > > > set as-path prepend 65500 65500 65500
> > > >
> > > > !
> > > >
> > > > R2
> > > > ++
> > > >
> > > > !
> > > > router bgp 65501
> > > >
> > > > neighbor 10.255.0.25 route-map AS_CHANGE out
> > > >
> > > > !
> > > > route-map AS_CHANGE permit 10
> > > >
> > > > set as-path prepend 65501 65501 65501
> > > >
> > > > !
> > > >
> > > > R1#sh ip bgp
> > > > BGP table version is 196, local router ID is 10.255.255.2 Status
> > > > codes: s suppressed, d damped, h history, * valid, > best, i -
> > > > internal,
> > > > r RIB-failure, S Stale, m multipath, b backup-path, x
> > > > best-external, f RT-Filter Origin codes: i - IGP, e - EGP, ? -
> > > > incomplete
> > > > Network Next Hop Metric LocPrf Weight Path
> > > > *> 10.3.0.0/16 0.0.0.0 0 32768 ?
> > > > *> 10.7.0.0/24 0.0.0.0 0 32768 ?
> > > > *> 10.11.0.0/24 0.0.0.0 0 32768 ?
> > > > *> 10.13.0.0/16 10.255.255.1 0 1
> 65501 ?
> > > > * 10.255.0.26 0 0 65501
> > 65501
> > 65501
> > > > 65501 ?
> > > > *> 10.16.0.0/24 0.0.0.0 0 32768 ?
> > > > *> 10.20.0.0/24 10.255.255.1 0 1
> 65501 ?
> > > > * 10.255.0.26 28416 0 65501
> > 65501
> > 65501
> > > > 65501 ?
> > > >
> > > > I need specific traffic from 10.100.60.11 (Source) to specific
> > 10.20.80.11
> > > > (Destination) over the 10.255.0.26 connection.
> > > >
> > > >
> > > > 10.100.60.11
> > > > _` 10.20.80.11
> > > >
> > > >
> > > > Any thoughts?
> > > >
> > > >
> > > > Blogs and organic groups at http://www.ccie.net
> > > >
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Received on Wed Jan 08 2014 - 17:52:46 ART