VPN Connection Loss for vpn client

Posted on 2006-03-28
Last Modified: 2010-03-19
I have a remote site that use PPPoE setup on the ADSL router (probably Aztech). I have installed the Cisco VPN client on two PC in this remote site. If both PC start the VPN connection at the same time, they will both loss the connection. However, if one PC start the VPN connection to my HQ and another VPN connection to my Asia Hub office (ie. two different peer address), both PC could work well without any connection loss.

Any idea and experience for that ?
Question by:AXISHK
    LVL 7

    Expert Comment

    you might be using NAT at your remote location and VPN server closed the connectons when it gets 2 request from same ip address.
    LVL 79

    Accepted Solution

    Yes. The router can only handle one VPN connection to the same remote end-point at the same time.
    You can use 1 PC to connect to two different remote sites at the same time
    You cannot use 2 PC's to connect to the same remote site
    You might not even be able to have 2 PC's connecting to 2 different end points
    It is partly in the way the Cisco end point is set up. Is it PIX, VPN3000 or other? Does it have nat-transparency enabled?
    Is is partly in the limitations of the DSL router.
    It is partly in the design of IPSEC VPN's.
    If you are behind a nat router, and the endpoint allows for nat-traversal, then both ends will use UDP port 4500.
    Traffic will be sent to you on UDP port 4500 through the router. The router's translation tables will recognize that traffic as belonging to your PC
    The 2nd PC, when estabilshing a new VPN tunnel will also negotiate for UDP port 4500 with the remote peer.
    Now your local router has two streams of data coming at it, both with destination UDP 4500 and the poor little DSL router simply can't tell the difference between which inside host to send it to. Inside host gets packets it was not expecting or no packets and both VPNs break down.
    More sophisticated firewall devices such as the Cisco PIX and handle more than one VPN client on the inside and can keep the traffic for each one separated.
    LVL 12

    Expert Comment

    it looks like if both are starting at hte same time, then the device that you are trying to reach sees that 2 connections are trying to be made from the same public IP,  if they do it at different times then it is ok,  am i correct?  also make sure that on the cisco client computers you have Local LAN Access checked.

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