thanks for the replies, maybe I'm getting the hang of this
time for a little ASCII art I think:
RA------RB------RC------RD------RE------RF------RG
L1 L1 L2 L2 L2 L1 L1
l1 l1/l2 l2 l2 l1/l2 l1
\__area-x____/\_______area-y________/\___area-z___/
l1 l1+l2 l1+l2 l2 l1+l2 l1+l2 l1
say you have a series of routers connected as above running IS-IS, as per
the first line.
second line is IS-IS Router type - ie Layer1 or Layer2
third line is adjacency type - ie layer1, layer1-2 or layer2
next line is areas, X, Y and Z, where Y would be the backbone, or OSPF area
0.0.0.0 equivalent
last line is the LS databases they carry
does this look about right? obviously the l1 databases will be different
between R-A/B/C and R-E/F/G as the l1 database refers to a different areas,
but apart from that?
I hope this is somewhere near correct as I have been hair-pulling over this
one. I have been finding Jeff Doyle's book very confusing as he continually
refers to L1/L2 routers - whereas I think he should say routers having L1-L2
adjacencies - a router can only be a Layer1 *OR* a Layer2 router (or IS I
suppose) for a particular area, right?
hope I'm making some sense, getting kinda late over this side of the pond
Andy
----- Original Message -----
From: "Doug Lockwood"
To:
Sent: Thursday, May 31, 2001 9:52 PM
Subject: RE: IS-IS queries [7:6638]
> 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=6697&t=6638
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