Re: Sham-link Clarification

I have been struggling with a similar issue. Try a virtual link through area
10 to PE1 then configure a sham link in Area 0. I know area 0 is not on the
PE2 CE2 side, but give it a try, unless I am going crazy and have something
else going on in my dynamips setup, this works. Then you can play with cost
to manipulate things. Otherwise I would love to hear some other solutions

On Thu, Jun 10, 2010 at 8:57 AM, Adrian Brayton <abrayton_at_gmail.com> wrote:

> Make sure that your domain IDs are the same.
>
>
> On Jun 10, 2010, at 9:53 AM, Nathan Richie wrote:
>
> > I am labbing up some various scenarios on MPLS and OSPF. From what I can
> tell
> > at this point, a sham-link works great if both the sites are in the same
> OSPF
> > area. However, from my what I can see in my results, it is not effective
> when
> > the 2 sites are in different non-backbone areas.
> >
> > So here is my topology:
> >
> > PE1---------PE2
> > | |
> > | |
> > CE1 CE2
> > OSPF OSPF
> > Area 10 Area 100
> > | |
> > | |
> > CE3 CE4
> > OSPF OSPF
> > Area 0 Area 100
> > | |
> > | |
> > CE5--------CE6
> > OSPF
> > Area 100
> >
> > CE1 always prefers the route to Area 100 via the backbone area. When I
> > disable the link between CE5 & CE6, it will use the sham-link between PE1
> &
> > PE2. Even though the Sham-link metric is lower. I am assuming it is
> because
> > of the requirement of OSPF to route inter-area through the backbone, but
> I
> > could be wrong.
> >
> > When link between CE5 & CE 6 is enabled
> > CE1#show ip route 2.2.2.2
> > Routing entry for 2.2.2.2/24
> > Known via "ospf 1", distance 110, metric 131, type inter area
> > Last update from 22.22.0.34 on Vlan3, 00:00:17 ago
> > Routing Descriptor Blocks:
> > * 22.22.0.34, from 22.22.3.3, 00:00:17 ago, via Vlan32
> > Route metric is 131, traffic share count is 1
> >
> > When link between CE5 & CE 6 is disabled
> > CE1#show ip route 2.2.2.2
> > Routing entry for 2.2.2.2/24
> > Known via "ospf 1", distance 110, metric 4, type inter area
> > Last update from 22.22.0.1 on Vlan5, 00:00:09 ago
> > Routing Descriptor Blocks:
> > * 22.22.0.1, from 22.22.0.1, 00:00:09 ago, via Vlan51
> > Route metric is 4, traffic share count is 1
> >
> > Two questions:
> >
> > 1) Why is it choosing the higher metric link over the lower-metric
> > sham-link?
> >
> > 2) Is there a way to route traffic through the sham-link instead of the
> CE5
> > - CE6 link?
> >
> >
> > Regards,
> >
> > Nathan Richie
> >
> >
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Received on Thu Jun 10 2010 - 09:14:32 ART