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
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