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New Member

What port does VPN use?

I have provided a vpn client to an external user. I have tested his account and login and it is functional. The user cannot connect to us. He says he cannot ping my gateway and gets the error "remote peer is no longer responding". He is asking me what port our vpn uses? I am thinking he believes that he is being blocked from his company firewall. Where is the best place to begin troubleshooting a problem like this?

Thanks in advance!

Louanne Fournier

Cisco Employee

Re: What port does VPN use?

Tunnel is built using UDP port 500 packets (ISAKMP).

Once the tunnel is up all the data transferred is with IP protocol 50 (ESP).

A lot of NAT/PAT devices will be unable to transfer the ESP packets properly, so you may have problems there, but you should at the very least be able to get a tunnel built properly cause the ISAKMP packets can be NAT/PAT'd properly.

New Member

Re: What port does VPN use?

The VPN Concentrator and the latest version of the PIX support UDP encapsulation - that will solve the issue of ESP not getting through the firewall.

If the user cannot even ping your device, the security policy at that end may be very tight.

New Member

Re: What port does VPN use?

Can you give me the syntax for the UDP encapsulation on a PIX FW, I can't find it anywhere ?

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