[j-nsp] ISIS Routing Problem

[Dan Evans]

Eric,

Since R1 and R2 are L1/L2 routers they'll each always prefer the L1 route
over the L2 route due to default route preference. It's an interesting
situation for sure. Removing the loopback from L1 isolates R1 and R2 from
advertising their loopbacks to R3 and R4, but with the loopback enabled for
Level 1 you'll always get the long path for R1 to R2 traffic.

 Do you require R1 and R2 to have L2 enabled on the R1--R2 link? You could
turn off L2 on that link and it should give you the result I think you're
expecting. R1 and R2 and still be L1/L2 or L2 only with any other upstream
routers to keep L2 continuity with any routers not in your original
topology.



On Wed, Jun 16, 2010 at 7:28 PM, Eric Van Tol <eric at atlantech.net> wrote:

> Hi all,
> I'm scratching my head over this one and I'm sure the answer is very
> simple.  I have four routers:
>
> R1 --- R2
> |      |
> |      |
> R3 --- R4
>
> R1 and R2 are L1/L2 routers.  R3 and R4 are L1-only routers.  Due to IOS's
> inability to do MD5 authentication at level 2, I cannot make R3 and R4 L1/L2
> routers.  R1 and R2 are running 9.6R3.8.  Now the problem...
>
> I have 'interface lo0.0 passive' configured on both R1 and R2.  The
> loopback is being injected into the L1 level, then being re-injected back
> into the L2 level when it's seen from R3 and R4.  I've tried messing with
> the preference values for level 2 on R1 and R2, but the loopbacks are always
> being preferred through the L1 level.  If I configure 'interface lo0.0 level
> 1 disable' on R1 and R2, the loopbacks disappear, but then I end up with BGP
> recursive route lookups from R3 and R4.  I'd prefer not to configure static
> routes for the R1 and R2 loopbacks on R3 and R4, but that seems to be my
> only recourse at this point.
>
> Am I missing something simple here or am I just going to have to do the
> static routes on R3 and R4, redistribute those between R3 and R4, but deny
> their redistribution up to level 2?
>
> Thanks,
> evt
>
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