John,
Have you considered going out to a movie, ballgame, or anything else that
might get you away from your routers for a few hours? :-)
--
James Haynes
Network Architect
Cendant IT
A+,MCSE,CCNA,CCDA,CCNP,CCDP
""John Neiberger"" wrote in message
[EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
> I have received results from a TAC case about this familiar issue. For
> those coming late to the picnic, the issue was that the presence of OSPF
> or IS-IS overrides 'no ip classless' in the router configuration and
> would force the router to behave classlessly. The TAC engineer
> consulted with some Development Engineers and here is what they said:
>
>
>
> Yes, we do this if the default (or the supernet) route
> is supplied by OSPF or ISIS (I guess EIGRP should be there,
> but it is not) and the part of the code that requested
> the RT lookup didn't not specify to ignore the default
> route if there's no specific subnet (which is the case
> for the locally originated and transit packets).
> The assumption is that it is safe to use a default/supernet
> route installed by a classless protocol.
>
> So what ever you and me have seen in our testing is correct behaviour.
>
>
>
> So, our original guesses were correct. The router assumes that if
> we're running OSPF or IS-IS then we want classless routing even if we
> didn't specify 'ip classless' in the config. However, an important
> point is that this applies only if the supernet was installed by the
> classless protocol. If OSPF or IS-IS is running on a router but the
> supernet was installed by another process, then classful routing would
> still apply without the addition of 'ip classless' to the config.
>
> I've also discovered that if you add 'ip clueless' to the config, the
> following occurs:
>
> First, ip classless is overridden but only in cases where no ip
> classless was manually configured previously and was not the default
> setting, unless the router has not had any previous configuration and is
> running at least 12.1(5F)T12. This does not apply for any 12.0 images
> except 12.0(6)S but does apply to any 11.2 image after 11.2(26c)P;
>
> Second, the gateway of last resort might be chosen by the RT lookup
> process if the GOLR was set by a classless routing protocol with an
> administrative distance lower than that of any other classless or
> classful routing protocol on the router, except in the case of BGP or
> EGP in which case the administrative distance must be at least equal to
> that of the routing protocol which previously installed the GOLR, if
> already present;
>
> Thirdly, if the lowest-weighted routing protocol is OSPF and the GOLR
> is advertised to neighbor as an E2 route, then the neighbor router may
> choose to use that route unless another neighbor has advertised the same
> supernet route as an E1 route. In which case--but especially when
> utilizing IP over Avian Carriers (with QoS)--the RT lookup will choose
> the Type 1 External route unless EIGRP is running on this router as
> well. In that case, the GOLR will be set via EIGRP because Cisco
> prefers EIGRP to OSPF and we should all use that anyway because, don't
> ya know, OSPF is harder to configure and requires way too much thought
> to begin with. IS-IS is just out of the question. However, if a router
> learns a supernet route via OSPF and IS-IS *and* EIGRP then you will be
> severely punished. Flogging is generally suggested. As an alternative,
> only run EIGRP and leave "ip clueless" configured.
>
> Any other configuration will provide ambiguous results.
>
> HTH,
> John
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