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Community Member

VPN Port Usage

I am having difficulty in transmitting data across a "connected" VPN tunnel. I believe certain ports may be blocked by an ISP (i.e port 500). I need info on what ports a VPN uses, and if Cisco makes a router that has port selectability for VPN applications? Can I select or try a different port thats available? Thanks


Re: VPN Port Usage

udp 500

udp 4500

ip 50

i believe these protocol/ports are industry standard and i believe that is not changeable.

regarding the issue, you mentioned "connected" vpn but no traffic. just wondering if you are referring to remote vpn or lan-lan vpn.

if it's a remote vpn and it's a pix, then perhaps try enable the nat traversal command. for pix, do a "isakmp nat-traversal"

Community Member

Re: VPN Port Usage

Thanks for the quick response. I am currently using two Linksys VPN routers. They "connect" but traffic doesn't flow - I cant ping either side within the tunnel. I dont have this problem with any other VPN's. I believe the ISP is blocking port 500 on the other side of my tunnel. What can I do to check this thoroughly and is there a Cisco router that may use a different port? Thanks!!


Re: VPN Port Usage

to verify, you may use a port scanner specifying the port and protocol.

i don't think any cisco device will use a different port

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Re: VPN Port Usage

I have a customer with a significant deployment of VPN. Our LAN to LAN VPN is based on router to router connection. But our client software based VPN terminates in a 3060 concentrator. When our software client VPN users have difficulty connecting with UDP 500 (which sometimes is blocked by providers) they have an option to connect using a TCP port. (It is a configuration option within the client, and works with our concentrators). I am not sure that terminating the client session on a router has the same capability but terminating on a 3000 concentrator it works well for us.



Community Member

Re: VPN Port Usage

Thanks. I believe the ISP is blocking UDP 500. Instead of using the Linksys routers I have now, what routers would you use if you needed to choose a different port? Is there a general setup you could give me that would work and allow port selection for VPN ? Thanks!!

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