Socket connection between multiple interfaces, through a router

[seets375]

Hi,

I have two ethernet interfaces on my system, with IPs assigned to the
interfaces from different subnets (e.g. eth1 - 10.10.10.10 and eth2 -
20.20.20.20 ). I'm connecting these interfaces to a home gateway or
router. The 'eth1' interface connects to LAN interface of the router
with IP address 10.10.10.1 and the 'eth2' interface connects to WAN
interface of the router with IP address 20.20.20.1.

I'm trying a simple socket program with C on Redhat Linux 9. I'm trying
to create a server socket (UDP or TCP) on my eth2 interface
(20.20.20.20), and a client socket (UDP or TCP) on my eth1 interface
(10.10.10.10). When I try to connect and send packets from eth1 to eth2
or vice-versa, the packets do not seem to pass through the router and
instead seem to create a local connection within the system. I verified
this with ethereal on both the interfaces eth1 and eth2). I wasn't
seeing any packets on these interfaces.

Just FYI, I was using AF_INET address family. I have routes
appropriately setup for the interfaces with 10.10.10.1 as the gateway
on the LAN side, and 20.20.20.1 as the gateway on the WAN side.

Why does the socket connection bypass the router? Is there a way to
ensure that my socket connection goes through the router, instead of
creating a local connection?

I'd appreciate if any one could help me with the solution to my above
problem, either with explanation or through sample code.

Thanks,
Seets.

 

[Ben Pfaff]

Why does the socket connection bypass the router? Is there a way to
ensure that my socket connection goes through the router, instead of
creating a local connection?

Your question is outside the domain of comp.lang.c, which discusses
only the standard C programming language, including the standard C
library. This is a remarkably narrow topic compared to what many
people expect.

For your convenience, the list below contains topics that are not
on-topic for comp.lang.c, and suggests newsgroups for you to explore
if you have questions about these topics. Please do observe proper
netiquette before posting to any of these newsgroups. In particular,
you should read the group's charter and FAQ, if any (FAQs are
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* OS-specific questions, such as how to clear the screen,
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news.groups.questions is a good place to ask about the appropriate
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[Keith Thompson]

I have two ethernet interfaces on my system, with IPs assigned to the
interfaces from different subnets (e.g. eth1 - 10.10.10.10 and eth2 -
20.20.20.20 ). I'm connecting these interfaces to a home gateway or
router. The 'eth1' interface connects to LAN interface of the router
with IP address 10.10.10.1 and the 'eth2' interface connects to WAN
interface of the router with IP address 20.20.20.1. [...]
I'd appreciate if any one could help me with the solution to my above
problem, either with explanation or through sample code.

Standard C has no networking support. Try comp.unix.programmer or one
of the Linux groups.

 

[seets375]

Sorry for posting to the wrong groups. And thanks for pointing me to
the right ones.

Thanks,
Seets.

 

[Keith Thompson]

Sorry for posting to the wrong groups. And thanks for pointing me to
the right ones.

A couple of tips:

Please don't top-post. See <http://www.caliburn.nl/topposting.html>.

Quoting context is good, but quote only what's relevant to your
followup. A few lines of Ben Pfaff's post would have been sufficient
to make the context clear.