From: Herbert Maosa (asawilunda@googlemail.com)
Date: Fri Aug 31 2007 - 17:35:52 ART
Thrown a little offset here. I thought the whole point of type-2 external
route was that the cost to ASBR was irrelevant ? If type-2 is looking at the
cost to the ASBR, then what is the difference with type-1 ?
On 8/31/07, Scott Smith <hioctane@gmail.com> wrote:
>
> While that is true that type1 metric changes along the path and the
> type2 is constant this isn't the point of the show output.
>
> What I've pointed out is there is another metric in play with
> externals aside from the metric of the route. The router also
> considers the cost to the ASBR when deciding if externals are truly
> equal. For two externals to be considered equal everything must be
> equal. Both the metric of the route as seen via "sh ip route" and the
> metric to the ASBR seen via "sh ip ospf border-routers" must be equal.
>
> --
> Scott
> CCIE #17040 (R&S)
>
>
> On 8/31/07, Gary Duncanson <gary.duncanson@googlemail.com> wrote:
> > Thanks for that Scott.
> >
> > Looks like this demonstrates this rather well, at least how I read it.
> >
> > From OSPF Design Guide on CCO.
> >
> > sic 'External routes fall under two categories, external type 1 and
> external
> > type 2. The difference between the two is in the way the cost (metric)
> of
> > the route is being calculated. The cost of a type 2 route is always the
> > external cost, irrespective of the interior cost to reach that route.'
> >
> > Rgds
> > Gary
> > ----- Original Message -----
> > From: "Scott Smith" <hioctane@gmail.com>
> > To: "Sadiq Yakasai" <sadiqtanko@gmail.com>
> > Cc: "Joseph Brunner" <joe@affirmedsystems.com>; "Herbert Maosa"
> > <asawilunda@googlemail.com>; "ISolveSystems" <support@isolvesystems.com
> >;
> > "Cisco certification" <ccielab@groupstudy.com>
> > Sent: Friday, August 31, 2007 7:49 PM
> > Subject: Re: OSPF external type-2 route load balance
> >
> >
> > > Bingo!
> > >
> > > A1 learns 100.100.100.0 from both 10.43.1.61 & 10.43.1.73.
> > >
> > > Before - BW 1536 to both ASBRs
> > >
> > > A1(config-router)#do sh ip route ospf
> > > 100.0.0.0/24 is subnetted, 1 subnets
> > > O E2 100.100.100.0 [110/20] via 10.43.1.61, 00:00:36, Serial1/0.1
> > > [110/20] via 10.43.1.73, 00:00:36,
> > > Serial1/0.2
> > >
> > >
> > > After - Dropped BW to 512 on s1/0.1
> > >
> > > A1(config-subif)#do sh ip route ospf
> > > 100.0.0.0/24 is subnetted, 1 subnets
> > > O E2 100.100.100.0 [110/20] via 10.43.1.73, 00:00:06, Serial1/0.2
> > >
> > >
> > > Then changed BW back to 1536 on s1/0.1 (now both are equal again)
> > >
> > > A1(config-subif)#do sh ip route ospf
> > > 100.0.0.0/24 is subnetted, 1 subnets
> > > O E2 100.100.100.0 [110/20] via 10.43.1.73, 00:00:02, Serial1/0.2
> > > [110/20] via 10.43.1.61, 00:00:02,
> > > Serial1/0.1
> > >
> > > The metric is a constant 20, however, for the externals OSPF also uses
> > > the cost to the ASBR.
> > >
> > > --
> > > Scott
> > > CCIE #17040 (R&S)
> > >
> > >
> > > On 8/31/07, Sadiq Yakasai <sadiqtanko@gmail.com> wrote:
> > >> Can you show the Type 4 LSA database as well?
> > >>
> > >> I think the cost to the ASBR has a role to play in selecting 2 Type 5
> > >> LSA's reporting the same prefix.
> > >>
> > >> I am not quite sure about this though.
> > >>
> > >>
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> > >
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-- Kindest regards, hm
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