Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!ames!pasteur!ucbvax!PARK-STREET.BBN.COM!brescia
From: brescia@PARK-STREET.BBN.COM (Mike Brescia)
Newsgroups: comp.protocols.tcp-ip
Subject: useful RR and SR (was: IP options crash our Sun gateway )
Message-ID: <8803181016.AA12766@ucbvax.Berkeley.EDU>
Date: 18 Mar 88 01:59:46 GMT
References: <20702@bu-cs.BU.EDU>
Sender: uucp@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 24


I have found source routing useful for tracing routes, both for local net
access problems and routing problems between gateways.  Today I had to bemoan
the fact that a particular gateway would not source-route, even though it did
not crash, because they had called to see why they could ping a core gateway
but not establish an EGP connection.  With source routing I send a packet from
gateway A to B and back to myself, and vice versa.  If it fails, I may get
ICMP net-unreachable for route problems, or host-unreachable for host access
problems.

One additional feature would make problem tracking useful; that is the ability
to ask a gateway to give back its opinion of the next hop for a particular
destination net.  This is the info that RR gives you, but only if the packet
gets back to you.  If gateway A wants to send to B and B is a black hole, you
would like to get the info from A instead.

I have been able to do source routing through 4.3BSD systems.  I think they
may do it even if IP_FORWARDING is off.

LSI11 core gateways do source-and-record-route but not record-route.
Butterfly gateways do both.  In both gateways, the alignment of the IP address
fields in the options is not critical.

Mike Brescia
BBNCC Gateway Development