[quagga-dev 5732] Re: show ip ospf route question

Joakim Tjernlund Joakim.Tjernlund at transmode.se
Fri Aug 15 19:14:57 BST 2008


> -----Original Message-----
> From: Andrew J. Schorr [mailto:aschorr at telemetry-investments.com]
> Sent: den 15 augusti 2008 18:29
> To: Joakim Tjernlund
> Cc: quagga-dev
> Subject: Re: [quagga-dev 5730] show ip ospf route question
> 
> On Fri, Aug 15, 2008 at 05:43:05PM +0200, Joakim Tjernlund wrote:
> > I have ospf enabled on a few ppp links on a none with source
> > IP address 192.168.101.77
> >
> > When I type show ip ospf route I get
> > ============ OSPF network routing table ============
> > N    172.16.6.29/32        [10] area: 0.0.0.0
> >                            directly attached to p1-3-3-3-4
> > N    192.168.101.77/32     [20] area: 0.0.0.0
> >                            directly attached to p1-3-3-3-4
> >                            directly attached to p1-12-3-12-4
> >                            directly attached to p1-11-3-11-4
> > N    192.168.101.96/32     [10] area: 0.0.0.0
> >                            directly attached to p1-9-3-9-4
> >
> > I see that I got a route to myself on 3 ppp interfaces, is this
> > normal? My old zebra based router does not show this.
> 
> I think this is almost "normal", but not quite.  These sorts
> of strange routes have been discussed many times on the list,
> for example here:
> 
>    http://lists.quagga.net/pipermail/quagga-users/2004-January/001382.html
> 
> If you have a router with a PtP interface configured with
> local address X/32 and remote peer address Y/32, then quagga
> typically sees a route to Y/32 as directly attached,
> and an additional route to the local address X/32 via the
> remote host (since the remote host is advertising a
> route to its peer X/32), with cost set to the sum of
> the costs of going over the link to the peer and then
> coming back.
> 
> Your config seems slightly different in that it is saying that
> X/32 is "directly attached" instead of saying "via Y, <ptp iface>".
> Is the cost 20 equal to the cost you've assigned to those interfaces,
> or is it twice the cost (for a round-trip)?
> Are you using vanilla quagga or a version with your unnumbered
> PtP patch?

Dunno about the cost ATM(I am at home), but I am using my
Unnumbered Quagga and in that one I make the nexthop's IP
address 0 in the SPF calculation, an interface route. This might
explain the difference I guess.

> 
> Arguably, in a better world, quagga would see that X/32 is
> actually a local address and suppress the route through
> the peer host.  In practice, it doesn't seem to affect actual
> routing, so nobody has bothered to try to fix this.  A patch
> would be nice so that people would stop asking about this...

He, He, let's see if my Unnumbered patches makes it into Quagga first.
I am quite happy with them, so I would very much like to have
them integrated, pretty please :)

 Jocke




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