Add loopback to bring VPN tunnel up?

Unanswered Question
Jan 30th, 2008

Hi, I have a Cisco 877 DSL router connected in a remote office with nothing connect to the Vlan1 (4 port switch on back) to bring the VPN up, how can I add a loopback to test the VPN is working?

I can ssh to the outside IP and back the change.

I have this problem too.
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cpubob Wed, 01/30/2008 - 12:12

if you have a rj-45 plug and a crimper, you can make a loopback plug. connect pin 1 to pin 3 and pin 2 to ping 6.

If you don't have a crimper you can do a Macgyver and take a cat5 cable, cut the end off and strip the jacket off to expose the wires. You want to connect pin 1, usually the white with orange cable, to pin 3, usually the white with green. Then connect pin 2, usually solid orange, to pin 6, usually solid green. Just strip off a little bit of the jackets and twist the cooper together. tape the exposed copper to prevent bad things from touching.


(The colors above are based on the 568B standard, there is also 568A which is the reverse, orange would be gree and green would be orange. )

Edison Ortiz Wed, 01/30/2008 - 12:29

Just create a loopback interface that matches the 'interesting' traffic at each end.

For instance, if your VPN ACL consist of:

access-list 100 permit ip

then on the source router, you need to configure

interface loopback 0

ip address

on the target router, then you need to configure

interface loopback 0

ip address


Once that's configured, then you can ping from the source by sourcing from the loopback

Example from router holding

ping source loopback 0


One caveat, you need to advertise those loopbacks either via static routing or dynamic routing. For this test, go with static routing.





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