RE: BGP AS-PATH PREPEND

Let me try to put this is perspective so that I help myself understand BGP
effectively. This is how I have setup in my lab.

Topology
++++++++

R1 (10.255.0.25) ------------------ (10.255.0.26) R2
|
|
(10.3.0.1) (10.13.0.1)
                        | |
                        | |
 (10.255.255.1) (10.255.255.21)
                             R3

R1 & R2 is directly connected. Think of it as P-2-P link, I call it Layer 2
connection.
R3 is a router in simulated MPLS cloud.
R1 second interface 10.3.0.1 is connected to R3 10.255.255.1
R2 second interface 10.13.0.1 is connected to R3 10.255.255.21

Objective
++++++++

1) All traffic
originated by users and systems in R2 that is accessing R1 will
utilize the MPLS cloud as the primary
path with the Layer 2 as their secondary
path.
2) Data replication traffic will only utilize Layer 2 as the primary path.
3) In the event connectivity between R1 & R3 is lost, all traffic should
traverse Layer 2.

-Yuri

> From: jeff_at_tydesystems.com
> To: marcabel_at_gmail.com; ebay_products_at_hotmail.com
> CC: sammybibs_at_gmail.com; mothafungla_at_gmail.com; ccielab_at_groupstudy.com
> Subject: RE: BGP AS-PATH PREPEND
> Date: Wed, 8 Jan 2014 10:45:09 -0700
>
> Marc,
> You are correct here. That's why I was asking where this host route was
> because I didn't see it in the BGP table and I didn't see a network
> statement advertising it (if it's in the IGP table already).
>
> 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
marc
> abel
> Sent: Wednesday, January 08, 2014 10:20 AM
> To: Cisco Fanatic
> Cc: Sam Bibby; Tony Singh; ccielab_at_groupstudy.com
> Subject: Re: BGP AS-PATH PREPEND
>
> That access-list isn't going to match any routes. Remember you are matching
> routes not flows so you can't specify a source and destination.
>
>
> On Wed, Jan 8, 2014 at 10:53 AM, 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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> >
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> >
> > >
> >
> > >
> >
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> >
> > >
> >
> > > ____________________________________________________________________
> > > ___
> >
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> >
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> >
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> >
> > ______________________________________________________________________
> > _
> >
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> >
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> >
> >
> >
>
>
> --
> Marc Abel
> CCIE #35470
> (Routing and Switching)
>
>
> Blogs and organic groups at http://www.ccie.net
>
> _______________________________________________________________________
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Received on Wed Jan 08 2014 - 10:11:33 ART