Re: ethernet interface perversity


Chris Torek (chris@gyre.umd.edu)
Tue, 25 Aug 87 19:04:10 EDT


(Apparently, someone wants a single Ethernet interface to respond to
ARP requests for several different Internet addresses.) Jim O'Toole
did something like this under 4.2BSD, with an `IP magic' hook whereby
all IP packets for one IP address were forwarded to a user-level
program. It takes about 15 minutes to figure out where and what to
write; we then had a user program that provided echo service a la
goonhilly-echo.arpa.

If all you want is for a 4.3 host to respond to multiple IP addresses,
this is even easier. Configure some unused interface with the alternate
address:

        # ifconfig lo1 a.b.c.d # or ifconfig sl1 a.b.c.d

Add it to your arp table:

        # arp -s a.b.c.d <your_ethernet_addr> pub

You should be set once the router picks up the address a.b.c.d from
interface sl0, or immediately if a.b.c.d is on the same `network'
as the 4.3 host as far as the sender is concerned. I tested this,
and gyre (128.8.128.77) did respond to packets for 128.8.128.200.



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