From: Robert DeVito (robertdevito@xxxxxxxxxxx)
Date: Mon Feb 05 2001 - 15:57:13 GMT-3
I also noticed, could be wrong, that the next-hop stays the same throughout
all your "BGP confederation peers". Has anyone else notice this? So if have
three AS's 1022,1033,1044 and all of them are confederated to AS 1, the next
hop will be constant throughout AS's 1022,1033,1044. Thoughts?
Robert
----Original Message Follows----
From: "Chris Mott" <cmott@home.com>
Reply-To: "Chris Mott" <cmott@home.com>
To: "CCIE" <ccielab@groupstudy.com>
Subject: RE: BGP Next hop self
Date: Mon, 5 Feb 2001 08:29:52 -0600
I've noticed the same thing ... fortunately the lab I was working had the
next-hop route (2 hopa away, of course) in the IGP, so it worked, but I
wonder how one would deal with this without an IGP to save the day ... any
thoughts?
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
Connary, Julie Ann
Sent: Monday, February 05, 2001 8:17 AM
To: Jeremy Gray
Cc: Fred Ingham; Alan Basinger; CCIE Newsgroup (E-mail)
Subject: RE: BGP Next hop self
Hi All,
I have also noticed the following about "next hop self". If you have
route-relflectors to
not have a full mesh. You receive an EBGP route on router A, you have
next-hop-self and it is sent
to the IBGP peer - router B with router A as the next hop. That IBGP -
router B - reflects the route to
another IBGP peer - router C. "Next-hop-self" does not work on the
route-reflector, it maintains
the next hop as router- A that originally received the external route. I
have not played
with confederations yet. This week.
Julie Ann
At 11:38 AM 2/4/2001 +0000, Jeremy Gray wrote:
>Here's a few tips.
>
>Next-hop-self - This typically being for IBGP sessions. EBGP will have
your
>outbound interface as the update-source for each update by default.
>
>You simply set this instead of advertising the subnet of the EBGP peer(s)
>into your IGP.
>
>For example lets say you're an ISP at LINX. You can either advertise the
>linx subnet in your IGP (redist connected, etc ) ; so that your IBGP peers
>who receive this update have the source (the external LINX LAN) subnet in
>their routing table and can therefore treat the EBGP routes from any LINX
>peers as valid (since the next hop reachable)....
>
>OR...
>
>You can set next-hop-self on the IBGP sessions to your IBGP peers on the
>assumption they know how to get to you... Because your source address is
>known or adverised in the IGP already.
>
>When you may not to use NEXT-HOP-SELF on an IBGP session...
>
>If you have a pair of routers on a shared NAP (say MEA-EAST1 and
MEA-EAST2)
>it may be more efficient to retain the EBGP next-hop when you advertise
>these routes to your IBGP peers.
>
>This is becuase ...When packets are then routed towards these routes they
>can then flow back to both of you border routers rather than 'one'. For
>example even if the original EBGP peering session was on your MEA-EAST1
>router, they can leave via MEA-EAST2, if the external nexthop route being
>followed via each routers recursive lookup used the best metric back to
>'mae-east subnet' instead of a specific host address. This is of course
>touching on design issues...
>
>When you don't care about the next-hop...
>
>If the EBGP peer is via a point-to-point subnet it makes no odds.. but you
>still MUST do one or the other, route the EBGP peers subnet or use
>next-hop-self.
>
>
>
>SYNC.
>
>A somehwat inappropraite default these days... Use this only if your EBGP
>peers are seperated with none-BGP router hops in your AS. And then
>redistributed the BGP routes into the IGP, the tow statements really go
>together SYNC = (redistributed into you IGP). Clearly this has limited
>value in the real world. The internet now has over 90k routes and even
the
>most robust IGP's are going to have trouble. In reality if you had to do
>this with teh entire internet, you'd need big-monster routers anyway - so
>you may as well run BGP on them, then you're back to "NO SYNC", since you
>really don't want to kill your IGP.
>
>In a lab scenario ... or other non INTERNET-SCALE network...
>
>EBGP routers are seperated by none-BGP routers. The none-BGP routers need
to
>have the same routes, so that if a BGP router forwards a packet via one of
>these routers the receiving router has somewhere they can send it (other
>than the bit bucket). The problem is that the EBGP router needs to know
>when the none BGP routers "are ready" to forward packets. Therefore they
>wait until they can see the routes in the IGP before they do. And thus
they
>are then "synchronised" with teh IGP and can actually use the BGP routes
to
>forward packets. Likewise they can then also advertise all synchronised
>routes to other EBGP peers as each route becomes 'synchronised'.
>
>
>NO SYNC.
>
>All routers between EBGP routers run BGP. THerefore packets routed across
>your network will be routable on each hop, since each hop as the full BGP
>routing table. No need to check if the route is in the IGP, coz its not.
>The the real world this is what you'll use.
>
>Update-source.
>
>Its a good common practice to set update-soure between IBGP peers to the
>loopbacks and this is useful when your routers have multiple interfaces
>because it creates resilience if an interface fails. The neighbor
statement
>to the to remote peer therefore points to your loopback address, and your
>neighbor statement points to theirs and you both use update-source
loopbackN
>
>Hopefully this clarifies rather than complicates....
>
>Regards, Jeremy.
>
>-----Original Message-----
>From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
>Fred Ingham
>Sent: 04 February 2001 03:06
>To: Alan Basinger
>Cc: CCIE Newsgroup (E-mail)
>Subject: Re: BGP Next hop self
>
>
>Alan: On the r1 neighbor statement only, assuming that r1 does not have
>the subnet between
>r2 and r3 in its routing table. You could also redistribute the r2-r3
>subnet into the r1-r2
>IGP. What did you see when you tried this out?
>
>Fred.
>
>Alan Basinger wrote:
> >
> > Hi all,
> > With only 2 weeks till me second attempt I am now in the panic mode.
> > Here is my question.
> >
> > r1 ------- r2 ------- r3
> >
> > r1 being in bgp as 10 and r3 being in bgp as 20 and r2 is the border
>router.
> > Would I use the bgp next hop self command on r2 pointing to both r1 and
>r3?
> >
> > Alan Basinger
> > Systems Engineer
> > SBC DataComm
> > Houston Texas
> > abasinge@swbell.net
> >
> > | |
> > ||| |||
> > .|||||. .|||||.
> > .:|||||||||:.:|||||||||:.
> > C i s c o S y s t e m s
> > Certified Gold Partner
> >
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