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XiotexStudios

Unreachable port on second network card

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Yes, I understand all that.

What I am saying is that if I transmit a UDP packet to another machine and there is nothing listening on the port I specify then the packet is essentially ignored - I see no bounce back traffic.

However, on a single card in the office if the port doesn't have anything listening it bounces back an ICMP unreachable port message. If I then attach a listener to that port the message goes away.

I have been writing network code on and off now since 1998 and its the first time I have seen this behaviour.

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I haven't used nmap yet - but I have downloaded it - cool tip!

Not so much typo as a collection of them... in combination with a lot of other work to do..

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Guest Anonymous Poster
Quote:
Original post by XiotexStudios
Yes, I understand all that.

What I am saying is that if I transmit a UDP packet to another machine and there is nothing listening on the port I specify then the packet is essentially ignored - I see no bounce back traffic.

However, on a single card in the office if the port doesn't have anything listening it bounces back an ICMP unreachable port message. If I then attach a listener to that port the message goes away.

I have been writing network code on and off now since 1998 and its the first time I have seen this behaviour.


This is caused by the firewall on the machine. If turned on, you can specify what kind of icmp messages are allowed. My machine for example never emits any icmp traffic. (no ping or port unreachable) On the local loopback, the firewall is not used so every icmp message gets through. The new windows firewall interace (winxp/sp2) hides the details, but this firewall was present since winn4/sp3, but it was turned off by default, and very few knew where and how to enable it. Also you had to specify filter rules much like you do with the linux ipchains module. The new (xpsp2) firewall system is more intelligent, much like iptables on linux but comes with a wizard interface that defaults everything to the common useage of the system. (so you better get a win2k3 server instead of winxp if you plan on hosting a game on windows)

Viktor

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Okay, that explains things...

And it's okay, the networking code is being developed on PC's for ease of development but the final platform is a console - so won't have these problems in the long run.

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