RFC1122, section 3.3.4.2:
<quote>
3.3.4.2 Multihoming Requirements
The following general rules apply to the selection of an IP
source address for sending a datagram from a multihomed
host.
(1) If the datagram is sent in response to a received
datagram, the source address for the response SHOULD be
the specific-destination address of the request. See
Sections 4.1.3.5 and 4.2.3.7 and the "General Issues"
section of [INTRO:1] for more specific requirements on
higher layers.
Otherwise, a source address must be selected.
</quote>
Do you guys think that the current Linux implementation might have
violated the "SHOULD BE" described above? Sorry for using the word
"violate"...
-nick
nick wrote:
> 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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