[rhelv6-list] routing/interface question

[Peter Ruprecht]

Hi everyone,

I think I'm seeing a difference in behavior between RHEL 5 and 6 on how 
packets get routed between different subnets on different network 
interfaces.  Say I have a dual-homed host, with each interface connected 
to a different physical class C subnet.  The routing table looks like:

# netstat -rn
Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt 
Iface
128.138.140.0   0.0.0.0         255.255.255.0   U         0 0          0 
eth1
128.138.107.0   0.0.0.0         255.255.255.0   U         0 0          0 
eth0
169.254.0.0     0.0.0.0         255.255.0.0     U         0 0          0 
eth0
169.254.0.0     0.0.0.0         255.255.0.0     U         0 0          0 
eth1
0.0.0.0         128.138.107.1   0.0.0.0         UG        0 0          0 
eth0

In RHEL5, if I ping the host's 128.138.140.X address from a machine on 
the 128.138.107. subnet, I can use tcpdump to see the icmp request 
coming in on eth1, and the reply going out on eth0.  The host is not 
doing forwarding; that is, there's a 0 in /proc/sys/net/ipv4/ip_forward.

Now, with what I think is exactly the same setup on a RHEL 6 host, I can 
see the incoming icmp packet on eth1, but there's no reply at all, on 
any interface.  Similarly for an incoming ssh request, for example.  If 
I ping the host's 128.138.140.X address from a machine on the 
128.138.140. subnet, then I see both the request and reply as expected 
on eth1.  And if I ping the host's 128.138.107.X address from a machine 
on the 128.138.107. subnet, then I see both the request and reply as 
expected on eth0.  iptables is not running.

Does anyone know if there's a way to get RHEL 6 to give me the behavior 
I'm used to with RHEL 5?  That is, how can I ping the interface on the 
"other" subnet and actually get a reply?

Thanks,
Peter Ruprecht