woods@ncar.UCAR.EDU (Greg Woods) (03/19/91)
> IP devices on different subnets on the same interface will > use the cisco to talk to one another even though they > are on the same physical cable. Not necessarily. We just run a default route to the router interface, and a class B netmask, and depend on proxy arp to get packets to things on different interfaces of the router (i.e. other subnets not on this same cable). It works for us. Since the netmask is class B, different net numbers on the same interface just speak directly to each other without going through the router. The router is smart enough to know which subnets it needs to proxy arp for on each interface (i.e. every subnet EXCEPT the ones on this interface, it will proxy arp for on this interface). --Greg
robelr@mythos.ucs.indiana.edu (Allen Robel) (03/20/91)
Who was it that said "Always check the RFCs first...?" Sorry for the last note! If the network interfaces on which the request was received and through which the route to the target passes are the same, the gateway must not reply. In this case, either the target host is on the same physical network as the gateway (and thus the host should reply for itself), or this gateway is not on the most direct path to the desired network, i.e., there is another gateway on the same physical network that is on a more direct path and the other gateway should respond. regards, Allen Robel robelr@mythos.ucs.indiana.edu University Computing Services ROBELR@IUJADE.BITNET Network Research & Planning voice: (812)855-7171 Indiana University FAX: (812)855-8299
robelr@mythos.ucs.indiana.edu (Allen Robel) (03/20/91)
Should have cited RFC1027 (Proxy Arp) in that last note... >If the network interfaces on which the request was received and >gateway must not reply. In this case, either the target host is on >the same physical network as the gateway (and thus the host should >reply for itself), or this gateway is not on the most direct path to >the desired network, i.e., there is another gateway on the same >physical network that is on a more direct path and the other gateway >should respond. allen
robel2@mythos.ucs.indiana.edu (Allen Robel) (03/20/91)
>same cable). It works for us. Since the netmask is class B, different >net numbers on the same interface just speak directly to each other >without going through the router. The router is smart enough to know which >subnets it needs to proxy arp for on each interface (i.e. every subnet This is not my understanding of how proxy arp works. The cisco manual explains in the section "Address Resolution using "Proxy Arp." (p. 5-9 of the Dec, 17th edition) that the cisco gives its *own* hardware address in the arp reply. The host that sent the request then uses the cisco's hardware address to get to the destination it enquired about. My assumption is that this is the case for multiple subnets on the same interface as well. Its easy enough to verify (or discount) this with an analyser so I'll do just that and write back with the results... regards, Allen Robel robel2@mythos.ucs.indiana.edu University Computing Services ROBELR@IUJADE.BITNET Network Research & Planning voice: (812)855-7171 Indiana University FAX: (812)855-8299