more interesting features of 4.2


Charles Hedrick (HEDRICK@RED.RUTGERS.EDU)
3 Jun 86 02:20:26 EDT


I have finally found a mechanism that seems to work for getting Suns
to route automatically. It turns out that you can specify
routing entries that will cause a host to treat destinations on that
network as local. I.e. it will issue ARP's for them, just as if
they were on the local Ethernet. The correct form is
   route add 0 <local-host-address>
if you want to set this up as a default. It turns out that all of
our diskless Sun 3's come up with such a default address
automatically. We believe that this is due to a bug, but it is a
fairly happy one, from my point of view. I have modified our
gateway software to be able to handle a network where the hosts
issue ARP's for everyone. The gateway responds to ARPs for hosts
on the other side of the gateway. It also responds to ARPs for
hosts on the other side of gateways that don't know about the
convention (giving their Ethernet address, of course, not its own --
this is an ARP-level equivalent of an ICMP redirect). This strategy
has a number of advantages from my point of view:
  - it requires no action on the part of the user, at least until
        Sun fixes their bug, if it is one.
  - the entry need not have wired-in knowledge of the gateway's
        address. If we change gateway configurations, this will
        continue to work.
  - if we have more than one gateway, and they talk to each other,
        we can take advantage of their redundancy, since we
        don't have specific routings built into the table.
I'm sure the gateway committee will come up with a more elegant
way to do things, but this looks like the best alternative to the
problem I have been posing for some time. It involves no
modification to Unix, does not depend upon hosts failing to
validate ICMP redirects, etc.
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