[c-nsp] C6500 IPv6 redistribute with route-map?

[Gert Doering]

Hi,

On Wed, Dec 11, 2013 at 07:01:56PM +0000, Nick Hilliard wrote:
> > Having a few 100 external(!) LSAs in an IGP won't make any of them sweat,
> > not even a stone-age cisco IOS 11.0 OSPF implementation on a 2500.
> 
> Mostly no argument there when everything is running smoothly, but from a
> design perspective, it is a lot cleaner to handle this stuff in ibgp.  You
> get a bunch of advantages, including stuff like continuous edge link flaps
> not trashing your entire network (before you pooh-pooh this, I have had to
> deal with the consequences of this on a sup720 based core with small
> numbers of prefixes in the igp and it's not pretty), 

Now this is actually something that interests me (and yes, I'm tempted to
pooh-pooh this).  With *external* LSAs, a flapping edge should be about
as expensive as flooding a BGP prefix throughout your network - each router
has to receive it, think about it, reprogram the (single) target network 
in the FIB.  No SPF needs to be run, no recursive next-hops need re-resolving,
etc. - so I wonder why the impact was so much higher for you.

(There whould be MRAI on BGP, to help tune down the effect of "fast flaps",
of course, but that doesn't apply for iBGP - OTOH "ip dampening" on IOS
is a wonderful thing and it's a shame they only do it for IPv4)

> being able to scale
> your network to arbitrarily large, consistently controlling distribution of
> prefixes around the place in a way that you just can't do with an IGP,
> implementing network-wide RTBH infrastructure, etc.

I'm not particularily advocating "doing it all without BGP", but I do
object to "it's in the textbook, thus everybody needs to do it that way!".

There's drawbacks to "customer prefixes in BGP" - and one of them is
"convergence is slower" plus "more potential for loops while reconverging"...

Of course, if your network spans multiple 100s of routers, and 10.000s
of customer connections, there is no alternative - but for a network with
single-digit routers, and below 100 LSAs, "operational simplicity" wins,
and I am fully convinced that "adding RRs" is not on the "simplicity"
side of things.

gert
-- 
USENET is *not* the non-clickable part of WWW!
                                                           //www.muc.de/~gert/
Gert Doering - Munich, Germany                             gert at greenie.muc.de
fax: +49-89-35655025                        gert at net.informatik.tu-muenchen.de
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 305 bytes
Desc: not available
URL: <https://puck.nether.net/pipermail/cisco-nsp/attachments/20131211/a6aa4aa5/attachment.sig>