From: ccie2be (ccie2be@nyc.rr.com)
Date: Wed Mar 09 2005 - 18:18:54 GMT-3
Hi Jonathan,
I've never used this myself but while doing an IE lab last week (lab 20), I
came upon a situation where one could and might want to use this feature.
First, think about the output of the show ip bgp command. You have a bunch
of columns one of which is the next-hop column.
Well, suppose you want or need to change the value in that column.
By using the set ip next-hop command within a route-map you can change the
value of the next-hop and thereby change this value of this attribute in the
BGP table as shown by the show ip bgp command.
Keep in mind, the way BGP sets and uses the next-hop value.
For example, rtr-1 in AS-1 is connected to rtr-2 in AS-2.
When rtr-1 advertises a route to rtr-2, it changes the next-hop value of
that route to that of it's outgoing interface connected to rtr-2. But, when
rtr-2 advertises this route with ibgp to its internal bgp neighbors, it
doesn't typically change the next-hop value (unless you config the nei
x.x.x.x next-hop-self command).
So, when you do show ip bgp on rtr-2, you'll see the routes learned from
rtr-1 will have a next-hop of rtr-1's outgoing interface.
But, now suppose rtr-2 is connected to another ebgp router rtr-3 on the same
ethernet subnet as rtr-1 and you want rtr-2 to use rtr-3 as the next-hop
instead of rtr-2. By using the set ip next-hop command, you can do this.
HTH, Tim
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Jonathan ZD
Sent: Wednesday, March 09, 2005 12:23 PM
To: Group Study
Subject: Re: set ip next-hop (BGP)
Thank you very much Dillon, However, I'm looking for "ip next-hop" under BGP
usage (not under PBR) as described under the following link:
http://www.cisco.com/univercd/cc/td/doc/product/software/ios123/123cgcr/iprr
p
_r/ip2_s1g.htm#wp1038254
I've read the explanatoin of command usage several times, still have no real
understanding of the topic.
Jonathan
----- Original Message -----
From: "Dillon Yang" <gzdillon@hotmail.com>
To: "Jonathan ZD" <Nuvo25@hotmail.com>
Cc: "Group Study" <ccielab@groupstudy.com>
Sent: Wednesday, March 09, 2005 8:28 AM
Subject: Re: set ip next-hop (BGP)
> Hi, Jonathan:
>
> There are two confusable command:
>
> 1.set ip next-hop IP address
> Forward Packet to the Indicated Next Hop if It Exists;
> If Not, then Use the IP Routing Table
>
> 2.set ip default next-hop IP address
> Forward Using the IP Routing Table if a Route Exists;
> If a Route Does Not Exist then Forward to the Next Hop
>
> HTH
> dillon
>
>
> ----- Original Message -----
> From: "Jonathan ZD" <Nuvo25@hotmail.com>
> To: "CCIE - GS" <ccielab@groupstudy.com>
> Sent: Wednesday, March 09, 2005 10:39 PM
> Subject: set ip next-hop (BGP)
>
>
> > Has anyone ever used the BGP "set ip next-hop" command (under
route-map)
> > with either IP-addr or peer-add? I've read the command guide from Cisco
Doc,
> > but still have no clue what they're talking about. If anyone ever use
and
> > understand this command, please kindly share the knowledge of how to use
this
> > command.
> >
> > Thanks.
> >
> > Jonathan
> >
> > _______________________________________________________________________
> > Subscription information may be found at:
> > http://www.groupstudy.com/list/CCIELab.html
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