Re: Sun routers...


Charles Hedrick (hedrick@topaz.rutgers.edu)
Wed, 26 Aug 87 22:41:05 EDT


Sun's Ethernet hardware is quite good. There's no reason in principle
why a Sun couldn't be a very good IP gateway. However there are some
practical things that make this less than optimal.

The versions of SunOS we have seen are based on 4.2. In order to
avoid stability problems, gateways have to have much more careful
validation of packets than 4.2 does. E.g. they have to recognize
every possible broadcast address format, and also refuse to forward
packets for invalid addresses (as opposed for example to sending ARP
requests for Martian addresses). This is somewhat better in 4.3 than
4.2, but even 4.3 does not recognize all possible old and new style
broadcast addresses, nor as far as I can tell does it have a complete
Martian filter.

We expect our gateways to do proxy ARP (for hosts that can't handle
subnets, and a few that can't even deal with routing). This is not
present in 4.2, and as far as I know is not in 4.3 either.

We expect our gateways to be up all the time. Normal timesharing
systems are taken down periodically for PM, software installation,
etc. Our gateways (cisco) download software from a server. Going to
a new release requires downtime of about 30 seconds. Suns typically
require a good deal longer than this to bring up new releases. Some
sites also take them down for backups, and now and then they crash
(though in honesty I'd have to say that our Suns are very stable).
I believe that the operational requirements of a gateway are at least
slightly inconsistent with those of a host.

If you are building a large or complex network, the vendors whose
business is making routers are likely to have better routing
technology than routed, to support a wider variety of media, (As an
example, we tried to interface our Sun to the Arpanet and found that
although 1822 interfaces existed, we couldn't find anyone who knew how
to get them.), and to be more aggressive about supporting new network
monitoring standards.

In the long run, there are going to be performance advantages. At
the moment, Suns probably perform at least as well at connecting
Ethernets as the typical dedicated routers.

We have used Suns as gateways between major Ethernets and restricted
Ethernets containing only diskless Suns. They perform very well at
this. I'm sure we will continue to use Suns as gateways to one extent
or another. However for large networks, those with complex
topologies, and those serving machines from many vendors (and with
buggy TCP implementations), I would recommend using a gateway from a
vendor that specializes in such things.



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