ISIS Up/Down bit

Robert_74Robert_74 Member Posts: 38 ■■□□□□□□□□
Not quite sure that this is expected behaviour.
From JNCIP study guide:
"Leak level 2 loopback addresses into area 49.0003 and ensure optimal routing to these prefixes."
- when making policy for leaking into level 1 on R3 or R4 we have one direct address which is not comining from L2 ISIS ( it is direct)
- so when it is redistributed on R4 into L1 it has UP/DOWN bit set
- R3 compares the lo0 from R4 - one from R4.00-00 level 2 and another one from R4.00-00 level 1
- level 1 has a better preference over L2, hence R3 will reach R4 through level 1 area rather then direct link

Unfortuantely this bit is missing from the book, and explicit "optimal route" does not hold the true here.

What is the solution here to reenforce optimal routing ??



  • hoogen82hoogen82 Member Posts: 272
    Unfortunately the only we can do it is possibly through making the link between R3 and R4 as a L1/L2 link...

    You are very right in your understanding, there was a discussion on this a while ago... and most of the engineers came to a conclusion that... the solution in the book didn't achieve optimal routing... Even the solution I proposed cannot be implemented if following the book... since I remember that on a one page.. It is shown as a L2 link...

    Most engineers agreed that it was only meant to show us ways to do things... and probably not to achieve the optimal routing goal... The case study has a similar task... but it works well there...

    IS-IS Sleeps.
    BGP peers are quiet.
    Something must be wrong.
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