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Question on IS-IS router types

SpunkerspawnSpunkerspawn Member Posts: 15 ■□□□□□□□□□
in CCNP
Ok, so I am almost done studying for my BSCI exam and I think I have a good enough grasp on each topic however there's one topic that's been bugging me for a while. And that is (as mentioned in the topic) the IS-IS router types.

Basically I want to know the difference between a Level 1-2 router and a Level 2 router. Why would we need a Level 2 router (or even a Level 1 for that matter) if the default config for cisco routers is Level 1-2?

Or let's say if we have a Level 2 what makes it essential that we cannot replace it with a Level 1-2?

I really need clarity on this subject because it's been eating away at my brain for a while :)

Thanks for the help and wish me luck on my BSCI exam!
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    kpjunglekpjungle Member Posts: 426
    Spunkerspawn wrote:
    Ok, so I am almost done studying for my BSCI exam and I think I have a good enough grasp on each topic however there's one topic that's been bugging me for a while. And that is (as mentioned in the topic) the IS-IS router types.

    Basically I want to know the difference between a Level 1-2 router and a Level 2 router. Why would we need a Level 2 router (or even a Level 1 for that matter) if the default config for cisco routers is Level 1-2?

    Or let's say if we have a Level 2 what makes it essential that we cannot replace it with a Level 1-2?

    I really need clarity on this subject because it's been eating away at my brain for a while :)

    Thanks for the help and wish me luck on my BSCI exam!

    Good luck on the exam!

    The reason why you dont want to have 1-2 routers everywhere is most likely because they will maintain two Link state databases, one for the level 1 and one for the backbone (level 2). Also, level 2 routers hand off default-information to level 1 routers in its area, so they can always "find their way out" of the level1.

    I think all in all it comes down to effeciency, you dont necessarily want to have the entire backbone routing table on all your routers.
    Studying for CCNP (All done)
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    SpunkerspawnSpunkerspawn Member Posts: 15 ■□□□□□□□□□
    Ah... that was the conclusion I came up with as well... it all comes down to efficient resource utilisation : ))

    Thanks for the reply!
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