From: Brian McGahan (brian@xxxxxxxxxxxxxxx)
Date: Sun Jul 14 2002 - 22:33:53 GMT-3
Good point Fred. I'll have to add that one to my bag of tricks.
Brian McGahan, CCIE #8593
Director of Design and Implementation
brian@cyscoexpert.com
CyscoExpert Corporation
Internetwork Consulting & Training
http://www.cyscoexpert.com
Voice: 847.674.3392
Fax: 847.674.2625
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Fred Ingham
Sent: Sunday, July 14, 2002 6:26 PM
To: Brian McGahan; 'Jonathan V Hays'; ccielab@groupstudy.com
Subject: Re: ISIS - subinterface needed?
Brian: I agree with your comments except for: " IS-IS will not run
over a
hub and spoke NBMA" Here is a counter example:
Say that R1 is the hub with a multipoint subinterface. R2 and R3 are
spokes using physical interfaces. All are in the same subnet, of
course.
Configure R1 as L1/L2 with net 49.0001.1111.1111.1111.00, R2 as L1 with
net
49.0001.2222.2222.2222.00, and R3 as L1/L2 with net
49.0002.3333.3333.3333.00. Assuming you have CLNS maps on your frame
cloud,
and ip router isis on the serial interfaces, R1 will form an L1
adjacency
with R2 and an L2 adjacency with R3.
This is part of an example that NMC-1 students configure with other
routers
connected off R2 and R3.
Cheers, Fred
----- Original Message -----
From: "Brian McGahan" <brian@cyscoexpert.com>
To: "'Jonathan V Hays'" <jhays@jtan.com>; <ccielab@groupstudy.com>
Sent: Friday, July 12, 2002 10:44 PM
Subject: RE: ISIS - subinterface needed?
> Johnathan,
>
> Actually there's a little more to it than that. With IS-IS,
> there are only two network types, point-to-point and broadcast.
Unlike
> OSPF however, there is no equivalent of the 'ip ospf network' command.
> The IS-IS network type is dependent on the interface type.
>
> Physical and multipoint NBMA interfaces are multipoint. The
> only big difference between them is that split-horizon is disabled on
> frame-relay physical interfaces. Point-to-point interfaces are (you
> guessed it) point-to-point. Like OSPF, the IS-IS network type must
> match for neighbors to become adjacent. Therefore, for two IS-IS
> routers to become adjacent over NBMA, you need to have a combination
of
> physical and multipoint, or two point to point interfaces. This leads
> us to two more issues that are worth mentioning.
>
> 1. IS-IS will not run over a hub and spoke NBMA
> 2. IP is not the transport protocol for IS-IS
>
> In regards to the first issue, this means that you must have two
> IP subnets if you are running a hub and spoke setup. Therefore you
must
> have two separate subinterfaces on the hub, or do a workaround such as
a
> GRE tunnel.
>
> Regarding the second issue, this means that physical and
> multipoint interfaces must have layer 2 to CLNS mappings. For
> frame-relay this translates to:
>
> frame-relay map clns [VC] broadcast
>
> This article should help to clarify some more.
>
> http://www.cisco.com/warp/public/97/isis-frint.html
>
> HTH,
>
> Brian McGahan, CCIE #8593
> Director of Design and Implementation
> brian@cyscoexpert.com
>
> CyscoExpert Corporation
> Internetwork Consulting & Training
> http://www.cyscoexpert.com
> Voice: 847.674.3392
> Fax: 847.674.2625
>
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
Of
> Jonathan V Hays
> Sent: Friday, July 12, 2002 5:11 PM
> To: ccielab@groupstudy.com
> Subject: RE: ISIS - subinterface needed?
>
> Thanks everyone for all the informative replies!
>
> Jonathan
>
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
> Jonathan V Hays
> Sent: Friday, July 12, 2002 2:17 PM
> To: ccielab@groupstudy.com
> Subject: ISIS - subinterface needed?
>
>
> Group,
>
> I just had an interesting experience configuring ISIS on two routers.
> One router (R1) had two serial subinterfaces, one of which was
> point-to-point to another router running ISIS (R2). Now R2 was not
> configured with subinterfaces, just "interface serial 0" since it was
> only connected to R1 (via frame relay). I could not get ISIS routes to
> appear in the routing tables of either router.
>
> After I changed R2 to a point-to-point subinterface the ISIS routes
> popped into both routing tables.
>
> The question is, why is the point-to-point subinterface necessary on
> both ends for ISIS to propagate routes?
>
> Jonathan
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