Routeing between two subnets not working

siva_bhavani · 12-25-2004, 06:52 AM

i have a linux machine with two Ethernet cards. one is connected to the subnet 161.9.0.0/16 and the address assigned is 161.9.220.1. the second card is assigned 161.8.220.1 and connected to the subnet 161.8.0.0(actually for testing, only one laptop with ip address 161.8.220.2 is connected) . iam able to ping 161.9.220.1 from the laptop and similarly, ping 161.8.220.2(laptop) from the linux machine. but iam not able to ping 161.9.220.2,3,4,5 from the laptop. what could be the reason? thanks in advance.
the distro is mandrake 10.0 with kernel 2.6

scowles · 12-25-2004, 07:11 AM

If I understand your post correctly, it sounds like you just need to enable ip forwarding.

Since I have never used mandrake, I can only give you the good ole fashion way of enbaling ip forwarding, but if mandrake uses sysctl, then you can enable ip forwarding using this utility. See: man sysctl

In the maen time, try the following command to see if this fixes your problem. you do NOT need to reboot to test.

Code:

[scowles@excelsior init.d]$ su
Password: 
[root@excelsior init.d]# cd /proc/sys/net/ipv4/
[root@excelsior ipv4]# cat ip_forward 
0
[root@excelsior ipv4]# echo "1" >ip_forward
[root@excelsior ipv4]# cat ip_forward  
1
[root@excelsior ipv4]#

Now test if you get a ping reply from the other subnet.

siva_bhavani · 12-28-2004, 07:59 AM

thanks a lot. i did sysctl -w /net/ipv4/ip_forward=1. that did the trick. both the sub nets are able to talk. the subsequent problem is this...

in one subnet, there is an application which sends out a message on udp broadcast on address 255.255.255.255. i want this to reach the other sub net. it is not. what needs to be done to get this going? it is reaching the linux router. but not getting forwarded...