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Webcast-Catalyst9k
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IS-IS Area ?

Hi,

Reading Doyle Vol 1 on IS-IS.

He states that "an IS-IS router resides completely within a single area".

While I can see that this is true for L1 or L2 routers, I think that an L1/L2 router must reside in both Areas by virtue of the fact that it holds Link State Databases for both L1 & L2 routers. If this is not the case then I can only conclude that an L1/L2 router must resides in one of the Areas. Doyle seems to indicate that the L1/L2 router resides in an L1 Area (the diagram p.599).

Can anyone help me to clear this up ?

Phil.

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Purple

Re: IS-IS Area ?

Phil,

An L1/2 router will reside in a single level-1 area. Level-2 is generally considered the backbone and not a separate area. The fact that a L1/2 router has the L2 database does not mean that it belongs to more than one area; it simply means that it has (possibly summarised) information from other areas.

The thing that Doyle is trying to convey is that the area boundary occurs between routers and not within them, as is the case with OSPF.

Paresh

1 REPLY
Purple

Re: IS-IS Area ?

Phil,

An L1/2 router will reside in a single level-1 area. Level-2 is generally considered the backbone and not a separate area. The fact that a L1/2 router has the L2 database does not mean that it belongs to more than one area; it simply means that it has (possibly summarised) information from other areas.

The thing that Doyle is trying to convey is that the area boundary occurs between routers and not within them, as is the case with OSPF.

Paresh

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