From: McCallum, Robert (robert.mccallum@thus.net)
Date: Mon Oct 20 2003 - 16:37:03 GMT-3
The area tag is required when you run multiple ISIS processes on the one box. The first process you configure is the level-1-2 process and from then on in the rest of the processes are level 1 only.
Robert McCallum
CCIE #8757 R&S
01415663448
07818002241
> -----Original Message-----
> From: ccie2be [mailto:ccie2be@nyc.rr.com]
> Sent: 20 October 2003 15:44
> To: Group Study
> Subject: IS- IS
>
>
> Hi group,
>
> I'm hoping to resolve a couple of IS-IS questions/issues:
>
> 1) In Doyle's Routing TCP/IP vol I chapter on IS-IS, he
> emphasizes the fact that in a IP only, multi-area IS-IS
> network, the IS-IS process doesn't know how to interpret the
> ATT bit which means that Level 1 routers don't know route
> packets to other areas. Doyle then presents two methods to
> overcome this problem.
>
> However, in the freely downloadable chapter on IS-IS from Cisco Press,
>
http://ciscopress.com/catalog/ccnp.asp?session_id={DFB54D2A-5AB6-4B7E-9BA1-BC
4657301EA4}
no mention is made of this issue and in the multi-area examples, multi-area routing works without employing either of the methods Doyle says is necessary.
Are Doyle's methods of overcoming this problem no longer needed? If so, why is that?
2) In Cisco's IS-IS documentation it says,
router isis [area tag]
Use the area tag arguments to identify the area to which this IS-IS router instance is assigned. A value for tag is required if you are configuring multiple IS-IS areas.
But, in all the examples I've seen in both Doyle and in the above chapter, the "router isis" didn't ever include an "area tag" even though the router might be connected to another area. Can someone explain and give examples of when the area tag is needed or not needed?
Thanks in advance, dt
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