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There are a few things that could go wrong, assuming that you have the server up (ie. you can connect, and you are currently connected to the Internet) ...
- You might have given the wrong IP address - some providers change addresses each session (especially dial-up), and also cable modem users tend to get a new address from a DHCP server. Check the address is still the same as the one you advised your friends.
- You might have more than one IP address - eg. a dial-up modem, an internal ethernet card, and a cable modem. You need to advise the address that they are connecting on.
- If you are behind a firewall the firewall may block certain ports. Even if you don't have one on your own PC, if you are running it at a school/college/business they may have one of which you are not aware. Even pinging isn't totally reliable, firewalls may block pings but let other traffic through, or vice-versa.
- If you are behind a server that is doing NAT (Network Address Translation, also known as "IP Masquerading") then incoming connections may not work. For example, I am doing that here. NAT lets you share one connection amongst more than one PC. This works fine on outgoing connections, but incoming ones need special treatment or they go only to the NAT server, not the PC at the end of the chain. If this is the case you need to configure "port forwarding". You would normally know whether or not this is happening to you. You can tell, to a certain extent, because the IP address at the "back end" of NAT is usually a "private" IP address, that is, one that is reserved for private networks.
These addresses are 192.168.0.0/16, 172.16.0.0/12 and 10.0.0.0/8. If your address looks like one of those then you may be behind a NAT server.
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- Nick Gammon
www.gammon.com.au, www.mushclient.com | top |
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