VPN tunnel will only intiate from one end

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Feb 4th, 2008
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Hi


I have a lan to lan VPN setup with 2 cisco pix 515e. One of the firewalls is in the uk and the other is in France. I can intiate the tunnel from France by pinging an IP address in the UK. If I ping France from the UK the tunnel fails at phase 2. Any idea why this is?


Thanks


Martin

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Richard Burts Mon, 02/04/2008 - 04:53
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Martin


In my experience there are several things that can result in the symptom that the tunnel can initiate from one end but not from the other:

- it may be that one end has a dynamically learned (and subject to change) IP address and the other end is configured to accept connection requests from any address and authenticate to determine if it is a legitimate peer. In this situation the peer with the dynamic address can initiate the tunnel but not the other peer.

- it may be that there is a mismatch between the peers about what is interesting traffic which can initiate the tunnel (perhaps echo request or echo response is included on one but not on the other).


If you get to phase 2 and fail I suspect it is the mismatch issue. Perhaps you can post the appropriate sections of both configs.


HTH


Rick

lord_studley Tue, 02/05/2008 - 01:39
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Thanks for the information. I can't get the configuration of the PIX in France as the tunnel is currently down. That PIX has a DHCP address on it's outside interface but it is connected to an ADSL router that has a fixed external IP address. That external address is the address the PIX in the UK looks for as a peer.


Would the DHCP outside interface make a difference?

Richard Burts Wed, 02/06/2008 - 21:03
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Martin


If you can not get to the config of the PIX in France, then the config of the PIX in the UK would be a good starting point.


I am having some difficulty in getting my head around how it would work for a PIX to have a DHCP address on its outside interface and to configure peering using the fixed address of the ADSL router. But I am wondering if this falls into the category that I described as one side has a dynamic address.


HTH


Rick

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