Hi folks,
Yesterday I asked a question on this mailing list regarding a
multi-homed host, and big thanks to Ralph's kind responose. But I think
i'm still puzzled by the symptom. So I'd like to rephrase my question as
follows:
My multi-homed host have two ethernet interfaces, their ip addreses
are not on the same subnet. The only routing rule is "default gateway
via eth0" besides the usual direct links.
This host may send out a packet spontaneously (f.e. I issue a ping
comand from this host), or send out a packet in response to a coming-in
packet (f.e. someone thousands miles away is pinging this host). In each
case, the outgoing packet must have a source address in its ip header.
In the first case, my guess is that the src addr would be determined by
the route (,therefore using eth0's ip). For the 2nd case, the "ideal"
src addr should be taken from the dst addr of the incoming packet.
Therefore, if someone is pinging my host through eth1's IP, then my host
should respond a packet whose src addr is eth1's IP.
Am I right? If my host is not behaving like this, what could have
gone wrong with my configuration? How can I trace this in the kernel?
Which kernel code should I look into for answer? linux/net/ip_output.c?
Linux's TCP/IP stack is huge to me, I kindof lost in it...
Thanks,
-nick
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