pinging linksys router from Linux box to internal network not working

illscience · 07-09-2008, 02:14 PM

Hi my Linux box has two ethernet cards installed. eth0 goes to the Net and eth1 to the linksys wireless router. eth1 has an ip of 192.168.1.1 and the router is 192.168.1.2. I can ping 192.168.1.1 but cannot ping the router at 192.168.1.2. I can also ping the Linux box from a laptop inside the internal network connect via wireless to the router, and can SSH into the box. Does anyone have any idea why I cannot ping the router?

forrestt · 07-09-2008, 02:26 PM

Is the router configured to respond to ping? I'm guessing it is not.

HTH

Forrest

sparc86 · 07-09-2008, 03:08 PM

You should check into your router firewalling settings if there's not any INPUT filter rule blocking ICMP packets.

farslayer · 07-09-2008, 03:17 PM

What interface on the Linksys router is connected to eth1 ? the WAN interface ?

Is your setup like this ?

Code:

Internet 
  |
  |
  |
eth0
Linux Box
eth1
  |
  | 
  |
WAN
Linksys Router
Internal
  |
  |
  |
Internal network

illscience · 07-09-2008, 04:18 PM

Quote:

Originally Posted by farslayer

What interface on the Linksys router is connected to eth1 ? the WAN interface ?

Is your setup like this ?

Code:

Internet 
  |
  |
  |
eth0
Linux Box
eth1
  |
  | 
  |
WAN
Linksys Router
Internal
  |
  |
  |
Internal network

Yes it's set up just like that. The router does respond to ICMP because I can ping it with a laptop connected to it.

forrestt · 07-09-2008, 05:42 PM

OK, then is your Linux firewall blocking icmp traffic?

Forrest

Edit: Never mind, I see you already answered that.

sparc86 · 07-10-2008, 12:13 AM

From which box are you trying to ping the router? Perhaps this box from where you're trying pinging the router has output ICMP filter rules blocking it.

Is it a Linux box? You can check the iptables rules from the same box using the following command:

Quote:

iptables -L

illscience · 07-10-2008, 07:38 AM

Quote:

Originally Posted by sparc86

From which box are you trying to ping the router? Perhaps this box from where you're trying pinging the router has output ICMP filter rules blocking it.

Is it a Linux box? You can check the iptables rules from the same box using the following command:

From the Linux box. OUTPUT defaults to ACCEPT. INPUT accepts icmp-request and icmp-reply.

farslayer · 07-10-2008, 07:40 AM

So is the 'Block WAN Requests' box checked in the router config ?

From the Linksys Router User Guide

Quote:

• By enabling the Block WAN Request feature, you can prevent your network
from being pinged, or detected, by other Internet users. The Block WAN
Request feature also adds another measure of security to your network by
hiding your network ports. Both functions of the Block WAN Request feature
make it more difficult for outside users to work their way into your network.

illscience · 07-10-2008, 07:44 AM

Quote:

Originally Posted by farslayer

So is the 'Block WAN Requests' box checked in the router config ?

From the Linksys Router User Guide

Hmmmm I'm not sure. That may be the problem. I'll give it a look when I get home.

Ok I just read that Block WAN Requests is enabled by default, and I didn't change it so that is likely the problem. Even with that being enabled I still was unable to get Internet access from inside the private network. I think it may have something to do with the iptables_nat module not being loaded. I'll have to check that when I get home as well.

farslayer · 07-10-2008, 08:18 AM

Your other issue is probably related to routing.. Each router needs to know what networks are located where. and you would need to add a static routing table on the Linux box in order for information from the internet to make it back to PC's on the inside of the Linksys Router.

Lets go back to our diagram for a minute, and add some addressing...

Code:

Internet - 64.210.41.1
  |
  |
eth0 - Public IP Address - 64.210.41.17
Linux Box
eth1 - 192.168.1.1
  |
  | 
  |
WAN - 192.168.1.2
Linksys Router
Internal - 192.168.0.1
  |
  |
  |
Internal network

Basically you need to add a route in the Linux box that say 'to get to 192.168.0.0 go through the next hop at address 192.168.1.2'

route add -net 192.168.0.0 netmask 255.255.255.0 gw 192.168.1.2

You should then have a new line in your routing table so it would look something like this...

Code:

it-etch:/# route
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
192.168.0.0     192.168.1.2     255.255.255.0   UG    0      0        0 eth1
192.168.1.0     *               255.255.255.0   U     0      0        0 eth1
64.210.41.0     *               255.255.255.0   U     0      0        0 eth0
default         64.210.41.1     0.0.0.0         UG    0      0        0 eth0

Let us know how you make out..