Subject: Re: question??

From: Vernon Schryver <[email-masked]>
Date: Wed, 5 May 1999 18:03:51 -0600 (MDT)

> From: Ari Ollikainen <[email-masked]>
> To: Guangsheng Liu <[email-masked]>

> >   Currently, we are trying to write a piece of code to find the default
> > gateway on the LAN ( avoid the manual configuration for every PC ).
> >   Does any body know if it is required for a router to support RFC 1256
> > "ICMP Router Discovery Messages"?
> >   If that's true, that will be great. If not, some advice will be highly
> > appreciated.

> >From RFC1812, Requirements for IP Version 4 Routers:
>
> 4.3.3.10 Router Advertisement and Solicitations
>
>    An IP router MUST support the router part of the ICMP Router
> ...

"Required by whom or what" should be asked.  Standards committee dreams
matters less in most universes than what really is.  To use ICMP Router
Discovery messages, both hosts and routers must understand them.  It would
be really swell if most hosts and routers spoke the protocol, but that's
not the way things are.  Judging from routers I saw delivered last week,
the most commonly available router discovery protocol is still RIPv1.
The second most commonly available protocol is RIPv2, and RFC 1256 might
not exist.  Thus, the prudent way to code a router-discovery program is
to send Router Discovery solicications, delay as required by RFC 1256,
and then send RIPv1 and RIPv2 queries as well as more ICMP messags.

The easiest path is to punt, and turn on RIP on the PC's, provided your
PC's are not so dumb that they don't have a RIP implementation.

Note that the `routed` in current versions of free BSD UNIX varients
likes to use that tactic of ICMP-and-then-RIP on single-homed hosts.

Vernon Schryver    [email-masked]

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From: Harald Tveit Alvestrand <[email-masked]>
Date: Thu, 06 May 1999 08:31:20 +0200

>likes to use that tactic of ICMP-and-then-RIP on single-homed hosts.

And don't forget trusty (????) old DHCP....

                  Harald

-- 
Harald Tveit Alvestrand, Maxware, Norway
[email-masked]

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From: Harald Tveit Alvestrand <[email-masked]>
Date: Thu, 06 May 1999 08:31:20 +0200

Harald