Destination Host Unreachable On Multiple eth and Multiple Gateway

sangprabv · 05-26-2010, 11:57 AM

I have three ethernet cards on my linux with these configuration:
eth0 202.153.193.193 netmask 255.255.224 (connect to internet)
eth1 192.168.8.1 netmask 255.255.255.0 (connect to LAN)
eth2 192.168.31.116 netmask 255.255.248 (connect to my partner)

And this is the routing table:
192.168.31.112 0.0.0.0 255.255.255.248 U 0 0 0 eth2
202.153.193.192 0.0.0.0 255.255.255.224 U 0 0 0 eth0
192.168.8.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1
0.0.0.0 202.153.193.193 0.0.0.0 UG 100 0 0 eth0

When I try to ping 192.168.31.113 which is the gateway for eth1 it returns "From 192.168.31.116 icmp_seq=1 Destination Host Unreachable"

How to make it able to ping 192.168.31.113? Thanks

anomie · 05-26-2010, 03:56 PM

What OS / version? Are you sure you need to be able to route to different gateways? IOW, what network(s) are you expecting the 192.168.31.113 gateway to route you to?

It seems more likely that you just need to be able to communicate with other hosts on the 192.168.31.112/255.255.255.248 and 192.168.8.0/255.255.255.0 subnets. (That doesn't require another gateway. You're already on the same LANs.)

If you really need to route to different gateways, read here:
http://www.linuxjournal.com/article/7291

Ipolit · 05-27-2010, 12:22 AM

It is not working with multiple default gateways.
You have to specify one

mac.tieu · 05-27-2010, 02:00 AM

Quote:

Originally Posted by sangprabv

I have three ethernet cards on my linux with these configuration:
eth0 202.153.193.193 netmask 255.255.224 (connect to internet)
eth1 192.168.8.1 netmask 255.255.255.0 (connect to LAN)
eth2 192.168.31.116 netmask 255.255.248 (connect to my partner)

And this is the routing table:
192.168.31.112 0.0.0.0 255.255.255.248 U 0 0 0 eth2
202.153.193.192 0.0.0.0 255.255.255.224 U 0 0 0 eth0
192.168.8.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1
0.0.0.0 202.153.193.193 0.0.0.0 UG 100 0 0 eth0

When I try to ping 192.168.31.113 which is the gateway for eth1 it returns "From 192.168.31.116 icmp_seq=1 Destination Host Unreachable"

How to make it able to ping 192.168.31.113? Thanks

Change your subnet mask of eth0 from '255.255.255.248' to '255.255.255.240' to include '192.168.31.113' address.

Cheers,
MT.

anomie · 05-27-2010, 06:57 PM

His netmask may be correct, but then his routing table entry would be bogus.

With the info given, the subnet range is: 192.168.31.113 - 192.168.31.118

His routing table shows:

Code:

192.168.31.112 0.0.0.0 255.255.255.248 U 0 0 0 eth2

@sangprabv: Check with someone who understands/manages these networks, and use the correct settings.

mac.tieu · 05-27-2010, 10:22 PM

Quote:

Originally Posted by anomie

His netmask may be correct, but then his routing table entry would be bogus.

With the info given, the subnet range is: 192.168.31.113 - 192.168.31.118

His routing table shows:

Code:

192.168.31.112 0.0.0.0 255.255.255.248 U 0 0 0 eth2

@sangprabv: Check with someone who understands/manages these networks, and use the correct settings.

You are right, i am mistaken.

anomie · 05-28-2010, 09:51 AM

No, you're fine.

You spotted the problem about a conflicting gateway and netmask. Now OP needs to clean it up.

sangprabv · 05-28-2010, 10:51 AM

Hi All,
Many thanks for the response. The gateway itself is OK. Since I have tested with a single NIC PC and apply manually the configuration. I can ping the gateway. The problem comes when I apply it on 3 NICs Linux box (I use Ubuntu Lucid).
But now it is all solved. I installed Shorewall and treat the traffic to 192.168.31.116/29 is dmz. I think it is all about IPTables. Thanks again for the effort on my case