Mailing List Archive: Cisco: NSP

Delayed IGP default-originate?

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kgraham at industrial-marshmallow

Nov 23, 2009, 10:29 AM

Post #1 of 5 (669 views)
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Delayed IGP default-originate?

Similar to Gert's question on on delayed eBGP startup, is there a good way
to delay IGP default-route generation?

Since our DFZ routers have a 0/0 nailed down to Null0, OSPF begins
generating the default right away, irrespective of BGP state (namely
before the router is actually prepared to handle default-routed traffic).
A delayed startup for OSPF doesn't work, since that same instance would be
needed to find iBGP loopbacks.

A route-map matching a "default-network" is the only thing that comes to
mind, though designating a magic prefix for this seems broken.

I don't believe there's a formal BGP state for "done w/ inital UPDATE
churn", but presumably this is where both the eBGP-startup and IGP-default
originate would ideally trigger.
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jaitken at aitken

Nov 23, 2009, 11:57 AM

Post #2 of 5 (619 views)
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Re: Delayed IGP default-originate? [In reply to]

On Mon, Nov 23, 2009 at 10:29:24AM -0800, Kevin Graham wrote:
> Similar to Gert's question on on delayed eBGP startup, is there a good way
> to delay IGP default-route generation?

router isis
set-overload-bit on-startup wait-for-bgp

router ospf
max-metric router-lsa on-startup wait-for-bgp

--Jeff

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jaitken at aitken

Nov 23, 2009, 12:14 PM

Post #3 of 5 (627 views)
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Re: Delayed IGP default-originate? [In reply to]

On Mon, Nov 23, 2009 at 07:57:19PM +0000, Jeff Aitken wrote:
> On Mon, Nov 23, 2009 at 10:29:24AM -0800, Kevin Graham wrote:
> > Similar to Gert's question on on delayed eBGP startup, is there a good way
> > to delay IGP default-route generation?
>
> router isis
> set-overload-bit on-startup wait-for-bgp
>
> router ospf
> max-metric router-lsa on-startup wait-for-bgp
>

Oops, hit 's' instead of 'e'. I meant to add: these commands do something
similar to what you're asking, and I think that they might what you actually
want; not only do you not want to generate a default route during initial BGP
convergence, you don't even want to be in the path (to a valid BGP NH) during
that period, for the same reasons.

Sorry, didn't mean to be extra terse. :-)

--Jeff

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gert at greenie

Nov 23, 2009, 1:58 PM

Post #4 of 5 (615 views)
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Re: Delayed IGP default-originate? [In reply to]

Hi,

On Mon, Nov 23, 2009 at 10:29:24AM -0800, Kevin Graham wrote:
> Similar to Gert's question on on delayed eBGP startup, is there a good way
> to delay IGP default-route generation?

I'm not sure if it helps for the "default-route" case, but you could try
"max-metric router-lsa on-startup 300" (under "router ospf ...").

This is similar to the ISIS overload bit - for the first 300 seconds,
OSPF will announce bad metrics, so that no other router will voluntarily
pick a path through the newly-booted router (if another path exists).

Loopbacks work, since there is no other path.

But as I said, I'm not sure if that works for default-route origination
as well.

gert

PS: this is one of my *other* problems - we use EIGRP for "carry loopback"
(which has much nicer fast-convergence properties than OSPF and ISIS
built right in...), and it has no similar mechanism, as far as I know.
*grumble at Cisco*.

--
USENET is *not* the non-clickable part of WWW!
//www.muc.de/~gert/
Gert Doering - Munich, Germany gert [at] greenie
fax: +49-89-35655025 gert [at] net

kgraham at industrial-marshmallow

Nov 23, 2009, 2:04 PM

Post #5 of 5 (628 views)
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Re: Delayed IGP default-originate? [In reply to]

> > router ospf

> > max-metric router-lsa on-startup wait-for-bgp
[...]
> not only do you not want to generate a default route during initial BGP
> convergence, you don't even want to be in the path (to a valid BGP NH) during
> that period, for the same reasons.

Yep, looks like that's it, thanks! Still leaving the LSA there as those LSA's
are still candidates in the event nothing else is available is more elegant
than I'd hoped for. (Should have read the 'delay eBGP sessions' thread more
closely...)
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