[j-nsp] ISIS Routing Problem

[Eric Van Tol]

I do need L2 enabled, as they are the two core routers, and as such, are the backbone of the network.  It's a good suggestion, though.  I'll probably end up just going the static route way, at least until I can swap these out with two almost-out-of-service Sup720s that can run some decent code.

As for the L1 route preference, that's what I don't understand.  If R1/R2 are getting each other's loopbacks through L2 with a preference of 18, but then I swap the L1/L2 preferences so that L2 now has a pref of 15, why would the L1 route always get preferred?

-evt

From: Dan Evans [mailto:pzdevans at gmail.com]
Sent: Wednesday, June 16, 2010 9:05 PM
To: Eric Van Tol
Cc: juniper-nsp
Subject: Re: [j-nsp] ISIS Routing Problem

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<mailto: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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