Two of my friend have a ps3 connect to a linksys router end have error "type nat" when he download game patch.

I'm not sure. But I do know that the "nat type" changed for me (I think to a 2 from a 3) when I enabled UPNP. So it might be worth trying to enable UPNP on the router.

My friend try it directly on the modem to, and the same error apear.

Seriously just start yelling at it that always works for the J man.

OOOO wait your not the J man............

Nat stands for network address translation, which is the way your router shows all traffic coming from your home network as one ip address. Your router and or ps3 config needs to be changed; hit I'm not a ps3 expert.

What is a J man ??

Dont bother asking.  Just know this, the real J Man would never talk about himself in the 3rd person.

Go to 'Network Settings' on the XMB and select internet test.

It will run a quick test on your PS3 and tell you your NAT type.

A NAT type of 1 or 2 is the most desirable with 3 potentially blocking communication between you and other players, as I understand it.

If you change the security settings on your router to medium or low that often drops the NAT type down to a 2 and if you get the password from your internet provider and enter it during the internet setup stage that can drop it to a NAT 1.

Some games will not work correctly based upon the type of NAT your router uses.  I know that I had serious problems with The Darkness as the multiplayer would not work with type 3 NAT.

NAT Type 1 - Directly connected to the Internet ... no NAT or connected in DMZ.

NAT Type 2 - NAT with dynamic port allocation (UPNP)

NAT Type 3 - Strict NAT with no UPNP

With type 3, it may not be possible to communicate with other PS3 systems, and voice / video chat and the communication features of games may be restricted.

It sounds to me that you have a router that doesnt support UPNP, and that the 2 PS3s are having problems with resource contention.  Your friends could try logging into the admin page of the router and checking to see if they can enable UPNP.  Depending on how old the router is, they might be able to update the router firmware to enable UPnP support.  If not, well the available options are few, and increasingly complex.