[AusNOG] Routing in NX-OS vs IOS

[Ben Byer]

On Thu, Nov 3, 2011 at 10:42 PM, Glen Turner <gdt at gdt.id.au> wrote:

> Ben wrote:
> > ....but wait!  I have multiple protocol clients using the same route-map
> - and maybe I *don't* want the change to be propagated to all of them at
> once as soon as I type "exit".  The way IOS allows you to change a
> route-map, then cause it to take effect on a per-peer basis via a soft
> clear, is operationally *useful*.
>
> It doesn't work that way. Changes to route-maps in IOS occur incrementally
> as typed. That's a major pain if you have a high ongoing rate of incoming
> BGP changes, as some of those incoming routes will meet a routing policy
> which is not either the new policy nor the old policy. That makes it
> essential to "clear .. soft in" each neighbour after a route-map change to
> regain a reasonable policy for all routes. Imagine changing an IOS
> route-map at a router connected to a peering point and you'll see what a
> PITA that is, especially when compared with how nicely JUNOS does the same
> thing.
>
> The only reason you see the "reasonable" behaviour you do is because you
> don't have a high rate of incoming route changes whilst you are altering
> the configuration.
>

Certainly, for the environment in which I'm using NX-OS I don't have a high
rate of routing changes.  But.  I do separately have IOS routers (mixture
of 12.2 and 12.4), and also 6500s running SXI code, connected to peering
points.  On each of them I find that clearing the BGP peering session is
required to make route-map changes take effect.  All the reference docs
I've found on CCO tell me that a "clear ip bgp" is definitely required.
What IOS are you running that puts the changes in your route-maps into
effect as you type?

> ...great - so now whether or not I type "exit", 60 seconds after I typed
> a command it will take effect...?  And this behaviour is documented only
> for the 7k, not the 5k?
>
> Does that behaviour still occur if you say "configure session ..."? In any
> sane world nothing would change until the "commit".
>

Looks like we do live in a sane world, and the "configure session" feature
will hold changes until you type "commit" .... but the feature at present
only supports ACL changes.  Which is a shame, it'd be nice to have it for
route-maps and prefix-lists too.

B
-- 
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[ e - ben.byer at gmail.com ]
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