From: Murali Raju (myccie@xxxxxxxxxxx)
Date: Sun May 27 2001 - 16:55:04 GMT-3
MEDs are only known to the direct peering AS (in this case the Service
Provider) not other upstream ASs. In other words using AS-Path Prepend
makes enforcing routing policies much efficient.
Murali.
-
Murali Raju
Sr. Network Consultant, CCNP
VIS, Inc
>From: alain faure <alainfaure@yahoo.fr>
>Reply-To: alain faure <alainfaure@yahoo.fr>
>To: ccielab@groupstudy.com
>Subject: RE: BGP Question
>Date: Sun, 27 May 2001 21:30:51 +0200 (CEST)
>
>Hello,
>
>Just a question, Is the two link from the same provider ?
>If so isn't it possible to use MED instead for as prepend ?
>If not why ?
>
>Best regards
>
>--- rsevier <rsevier@zealousolutions.com> a icrit : > Matt is correct.
>Below
>is a sample config. Check it carefully because I
> > put it together quickly. Notice as-path 3, that is there to not have
> > packets coming from williams to have to out their network to come in
>L3's
> > connection. this will allow the williams packets to come in through the
> > william's connection and not to touch L3's network at all.
> >
> > matt- say hi to Ken Walls and Eddie for me.
> >
> > neighbor x.x.x.x remote-as 3356
> > neighbor x.x.x.x version 4
> > neighbor x.x.x.x route-map from-willims in
> > neighbor x.x.x.x route-map TO-williams out
> > neighbor x.x.x.x remote-as 3356
> > neighbor x.x.x.x version 4
> > neighbor x.x.x.x route-map from-willims in
> > neighbor x.x.x.x route-map TO-williams out
> >
> > neighbor x.x.x.x remote-as (william's AS)
> > neighbor x.x.x.x ebgp-multihop 2
> > neighbor x.x.x.x update-source Loopback0
> > neighbor x.x.x.x version 4
> > neighbor x.x.x.x route-map from-L3 in
> > neighbor x.x.x.x filter-list 10 out
> >
> >
> > ip as-path access-list 1 permit .*
> > ip as-path access-list 2 permit ^$
> > ip as-path access-list 3 permit ^(williams AS)$
> > ip as-path access-list 10 permit ^$
> >
> > route-map from-L3 permit 10
> > match as-path 1
> > set local-preference 150
> > !
> > route-map from-williams permit 10
> > match as-path 3
> > set local-preference 160
> > !
> > route-map from-williams permit 20
> > !
> > route-map TO-willaims permit 10
> > match as-path 2
> > set as-path prepend 3356 3356 3356 3356 3356 3356 3356 3356
> >
> > Raymond
> >
> >
> >
> >
> >
> >
> > -----Original Message-----
> > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
> > Matt.Wilkerson@Level3.com
> > Sent: Tuesday, May 22, 2001 7:41 AM
> > To: oriya@techiesclub.com
> > Cc: ccielab@groupstudy.com
> > Subject: RE: BGP Question
> >
> >
> > Finally... 1 I can contribute on :>)
> >
> >
> > You need to use a route-map on your bgp "neighbor x.x.x.x" statements.
>There
> > are 2 directions of traffic you need to influence, your inbound traffic
>and
> > your outbound traffic. This can most easily be done by adjusting the "as
> > path" and the "local pref" attributes.
> >
> > On the outbound route-map, you'll need a "match" statement which will
>permit
> > any, followed by a set statement, which will prepend your AS a couple
>times
> > on the Williams link. This will make your williams link appear to have a
> > longer route, than the Level3 path. Which will shift your incoming
>traffic
> > to the Level3 link.
> >
> > ex. L3- 3356-YourAS
> > Williams 5555-YourAS-YourAS-YourAS-YourAS
> > <----this appears a longer route
> >
> > To affect your outbound traffic, you'll need to tag the Level3 link with
>a
> > higher "local-pref" See the short examples below...
> >
> >
> > #######################################
> > route-map Williams-Outbound-Map permit 10
> > match ip address 1 <---------references access list 1
> > set as-path prepend 3356 3356 3356
> >
> > route-map Level3-Inbound-Map permit 10
> > match ip address 1 <--------Same here
> > set local-preference 200
> >
> > access-list 1 permit any
> >
> >
> > router bgp YourAS
> > neighbor 1.1.1.1 route-map Williams-Outbound-Map out
> > neighbor 2.2.2.2 route-map Level3-Inbound-Map in
> > ######################################
> >
> >
> >
> >
> >
> >
> >
> > -----Original Message-----
> > From: Oriya Pollak [mailto:oriya@techiesclub.com]
> > Sent: Tuesday, May 22, 2001 11:09 AM
> > To: ccielab
> > Subject: BGP Question
> >
> >
> > Let me ask you all a question.
> >
> > I have BGP running between our router to our 2 Internet uplinks - Level3
> > Communications and Williams Communications. I would like to push almost
>no
> > traffic or not at all to Williams but I do want to have it up in case
>level3
> > goes out and traffic needs to go on Williams.
> >
> > Any ideas?
> >
> > Oriya
> > **Please read:http://www.groupstudy.com/list/posting.html
> > **Please read:http://www.groupstudy.com/list/posting.html
> > **Please read:http://www.groupstudy.com/list/posting.html
>=====
>------------------------------------------------------------
>alainfaure@yahoo.fr
>Computing networks & internet specialist
>Certified Cisco(ccna,ccnp),Microsoft(mcse),Novell(cna)
>tel./fax. 33 (0)1 45 87 95 07 PARIS(FRANCE)
>------------------------------------------------------------
>
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