Andy
L1 and L2 refer to the Dyxtra(sp.) Routing processes Running on the router.
In ospf, its one for each area the router is in.
In ISIS, its L2 if the router is connected to a router in another area(an
ABR), L1 if it is only connected to routers within its area, and L1/2 if it
needs to be aware of both inter and intra area routers.
The Key to all of this is to realize that an ISIS router is only in one
area. In ISIS, routers are in an area, wile networks connect areas. In
OSPF, a router is in many areas while lan's are in only one area.
"Obviously the adjacencies between the L1/L2 and L1 routers should be
circuit-type-l1, but should the adjacency between the L1/L2 (pseudo-ABR I
suppose) and the L2 (backbone) routers be circuit-type-l1-l2 or l2?"
The L1 to L1/L2 in the same area are shared on the L1 process.
L1/2 to L2 (or L1/2) in are on the L2 process, whether they are in separate
areas or the same area.
"Finally, is it recommended to run full CLNS routing throughout, and if so
what are the advantages?"
The advantages of integrated ISIS (TCP info) are similar to ospf, with the
added benefit that any two connected areas do not have to traverse a
"backbone" area, unless it is the best path.
"the numbering of areas is arbitrary" yes! an area is a logical group of
routers that share a SPF view. ISIS is link state within an area, and link
state BETWEEN areas. Within an area, the link state is designated L1,
Between areas L2.
Hopefully, I have answered some of your questions without mudding the water.
HTH
Doug
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=6663&t=6638
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