Re: Subnetting


jqj@hogg.cc.uoregon.edu
Tue, 10 May 88 16:21:11 PDT


> The Internet standard approach for a host: pick any
>gateway and let it redirect you... is simple and effective. ....
but works abysmally given the typical host software that allows you
either to (1) set a static default route to the world, or (2) run
passive RIP or something like it. If I choose option 1 and the default
gateway crashes, it won't be around to send ICMP redirects telling me
to use the backup gateway. Phrased differently, the "Internet
standard" does not adequately address the issue of how a host should
pick the first gateway to try.

>You REALLY DON'T want hosts to know about routing.
At issue here is a critical point: how smart is it desirable for hosts
to be? Braden argues that they should be very dumb. I would argue
that they can be dumb if they don't really need connectivity off their
network, but should be a little bit smarter if possible. If you
concede that, then the next step is to decide whether it is better for
a host to have: (1) a static list (n>1) of gateways to try; (2) some
as yet undefined dynamic discovery mechanism for a host on a network to
find the list of gateways without getting routing data; (3) hosts that
listen to routing traffic and hence could potentially use the data to
avoid that first bad choice of a gateway.

My personal bias: Passive RIP works just fine in the XNS world as a HOST
protocol as well as as a gateway protocol. It works adequately in the
IP world for typical CANs and moderately complex LANs. I see no real
alternative available at present.



This archive was generated by hypermail 2.0b3 on Thu Mar 09 2000 - 14:42:13 GMT