IP-Ethernet Routing Problem (4.2)

[Peter Vanderbilt]

How can one explicitly route to certain hosts through a particular ethernet
interface?  At boot time on host usc-cse, we use

    ifconfig il0 -trailers arp usc-cse

to initialize the interface and establish a uscnet-to-il0 route.  At this
time, communication to usc-cseb (on uscnet) works.  BUT, if I try the simple
experiment

    route add usc-cseb usc-cse

communication between usc-cse and usc-cseb stops!  (Using "telnet usc-cseb"
results in an immediate "connection closed by foreign host"; this is without
the "ifconfig il1" or any other Bnet routing, as discussed below).  "Netstat
-r" shows:

    Routing tables
    Destination     Gateway         Flags    Refcnt Use        Interface
    usc-cseb        usc-cse         UH       0      520        il0
    loopback-net    localhost       U        0      10161      lo0
    uscnet          usc-cse         U        1      378483     il0

Once the usc-cseb route is deleted, communication is restored.  My suspicion
is that an ethernet interface can't handle packets routed to it as a host
(i.e. you can have networks and gateways as destinations but not hosts).

What's going on?  Any suggestions?  (We have a VAX 750 running BSD 4.2 with
two Interlan ethernet boards).

Why do we want explicit routing?  We want to use our VAX as a gateway between
two ethernets.  Unfortunately, for reasons beyond our control, we are not
allowed to assign different Internet network numbers to the two ethernets
(apparently we are not allowed to have a "remote" net behind the arpanet
gateway).

My plan is to route directly to all local hosts, on ethernet A, and then
wildcard route to hosts on ethernet B and the rest of the world:

    # Name interfaces and remove default routings
    ifconfig il0 -trailers arp Anet-gw
    ifconfig il1 -trailers arp Bnet-gw 
    route -f
    # route local hosts out il0 (net A)
    for host in <local-host-list>
    do
	route add $host Anet-gw
    done
    # route B hosts out il1
    route add uscnet Bnet-gw
    # route the rest through gateway (brand on B)
    route add 0 brand   .

(Perhaps the order of routing calls needs to be reversed).  Uscnet is
192.5.10 in /etc/networks and /etc/hosts has

    192.5.10.255	usc-cse cse usccse csea usc-csea usccsea Anet-gw
    192.5.10.248	usc-cse Bnet-gw
    192.5.10.254	usc-cseb cseb usccseb 
    192.5.10.61		brand

Are there other ways to accomplish the same thing?  Other suggestions?

Thanks.

Pete
-- 
Peter Vanderbilt
  uucp:  ...!{{decvax,ucbvax}!sdcsvax,hplabs,allegra,trwrb}!sdcrdcf!uscvax!pv
  csnet: pv at usc-cse
  arpa:  pv at usc-cse.csnet (or pv%usc-cse at csnet-relay.arpa)