Take the 2-minute tour ×
Server Fault is a question and answer site for professional system and network administrators. It's 100% free, no registration required.

I have 4 machines

machine 1 has ip address
machine 2 has two ip address and
machine 3 has two ip address and
machine 4 has ip address

machine 2 and 3 have NAT on both ways

we can ping from machine machine 1 to machine 4 and vice versa

I need a tunnel to be formed between machine 1 and 4

I used following commands

ip tunnel add gtt0001 mode gre remote local ttl 255 dev eth1
ip link set gtt0001 up
ip addr add broadcast dev gtt0001
ip link set gtt0001 multicast on
ifconfig gtt0001 netmask 
ip route add dev gtt0001
iptables -t mangle -A POSTROUTING -p tcp --tcp-flags SYN,RST SYN -o gtt0001 -j TCPMSS --clamp-mss-to-pmtu

similar commands on machine 4

But I cannot ping from machine 4 (IP and vice versa

share|improve this question
Asking the same question twice doesn't get you twice the help. –  womble Jul 16 '11 at 11:48
Enhance your previous question, don't ask a new one which is indistinguishable from the previous one. Make that question good enough, and you might just get an answer. –  womble Jul 16 '11 at 22:36
Re-opening this question since it is no longer a duplicate. Carry on. –  sysadmin1138 Jul 19 '11 at 12:10

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Browse other questions tagged or ask your own question.