From: Edward (edwlui@gmail.com)
Date: Fri Aug 31 2007 - 18:59:50 ART
Scott,
Thanks for demonstrating the difference between them.
:-)
Edward Lui
On 8/31/07, Scott Smith <hioctane@gmail.com> wrote:
>
> We're specifically talking about load balancing type2 externals here.
>
> Type 1 Example
>
> Before - equal BW on both paths
>
> A1(config-subif)#do sh ip route ospf
> 100.0.0.0/24 is subnetted, 1 subnets
> O E1 100.100.100.0 [110/85] via 10.43.1.73, 00:00:02, Serial1/0.2
> [110/85] via 10.43.1.61, 00:00:02,
> Serial1/0.1
>
> **************************************
>
> After - changed BW on s1/0.1 to 512
>
> A1(config-subif)#do sh ip route ospf
> 100.0.0.0/24 is subnetted, 1 subnets
> O E1 100.100.100.0 [110/85] via 10.43.1.73, 00:00:01, Serial1/0.2
>
>
> **************************************
>
> Here I've shutdown s1/0.2 so we can see the route from 10.43.1.61 is
> there but the metric is higher because I changed the BW to 512 and the
> type1 metric includes the cost along the path.
>
> A1(config-subif)#do sh ip route ospf
> 100.0.0.0/24 is subnetted, 1 subnets
> O E1 100.100.100.0 [110/215] via 10.43.1.61, 00:00:15, Serial1/0.1
>
> **************************************
>
> Notice with the type1 the metric changes so it is the deciding factor.
> We know the cost to the ASBR is not equal because if it were the
> metric would be equal.
>
> --
> Scott
> CCIE #17040 (R&S)
>
>
> On 8/31/07, Herbert Maosa <asawilunda@googlemail.com> wrote:
> > 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.
> > > > >>
> > > > >>
> > _______________________________________________________________________
> > > > >> Subscription information may be found at:
> > > > >> http://www.groupstudy.com/list/CCIELab.html
> > > > >
> > > > >
> > _______________________________________________________________________
> > > > > Subscription information may be found at:
> > > > > http://www.groupstudy.com/list/CCIELab.html
> > >
> > >
> > _______________________________________________________________________
> > > Subscription information may be found at:
> > > http://www.groupstudy.com/list/CCIELab.html
> > >
> >
> >
> >
> > --
> > Kindest regards,
> > hm
>
> _______________________________________________________________________
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