Here I have tried to list the most common server errors one might encounter while on Undernet.
NOT ENOUGH BUFFER SPACE AVAILABLE
This means mIRC is having a problem getting a network socket; it cannot use your Internet connection to connect to an IRC server. If you are using a lot of other network applications at the same time, you might get this error. Close some other applications and/or reset your Internet connection to fix this problem.
NO ROUTE TO HOST
Unable to connect (no route to host) This normally means you are not properly connected to the Internet. Your Windows cannot find out how or where to find the IRC server. It has nothing to do with mIRC or IRC. Check your connection (reconnect if everything seems fine) and try again.
UNABLE TO RESOLVE IRC SERVER
This means your providers' DNS is broken, the server no longer exists under that name, or you typed its name incorrectly. This has nothing to do with mIRC or IRC. Try another server.
CAN'T ASSIGN REQUESTED ADDRESS
Unable to connect (Can't assign requested address) This means the IRC server is unreachable for everybody. Most probably the admins have tweaked their DNS records to point to the non-existent IP number 255.255.255.255 to detour a DDoS (Distributed Denial of Service) attack. Try another IRC server or network. (When they set the server IP address to be 255.255.255.255 you will get the error "Can't assign requested address." When they set it to 127.0.0.1 you will get the error "Connection refused." If they disable the address altogether (set it to nothing) you will get the error "Unable to resolve IRC server.")
CONNECTION TIMED OUT
Unable to connect (connection timed out) Things can get slow on the Internet. Either when you try to reach a far away server or when connections somewhere in between your Internet provider and the IRC server are broken. Very often you didnt have a (proper) connection to the Internet even before you started mIRC. Patience is usually the best option here. Try it again in a few minutes or try another IRC server. This has nothing to do with mIRC. There is not something you can magically fix.
FORWARD AND REVERSE DNS DO NOT MATCH
Your forward and reverse DNS do not match, ignoring hostname. Closing Link: 22.214.171.124 (You are not authorized to use this server) The server cannot (properly) resolve your IP Number to an IP Name. Your Internet Provider has to fix his DNS system. Until then try another server on the same IRC network.
SEEMS THAT YOU DON'T HAVE IDENTD INSTALLED ON YOUR HOST NO IDENT FOUND
If you get Ident related problems you have not activated the built-in Ident server in mIRC, or it is blocked by a firewall, router or proxy (like Internet Connection Sharing). More and more IRC servers require you to be identified in some way, and they will disconnect you if you are not identified! In mIRC go to File/Options/Connect/Identd/ and enable the Ident server. You can check if you're properly identified by doing a /whois on yourself. The first line in the reply should NOT contain a ~ (tilde) or a - (minus) before your userid. If you have a ~ or a - in it try activating the Ident server built into your IRC client or use a separate Ident server and restart your IRC client and see if it helps. Opening port 113 in your firewall or router is essential as well.
Closing Link: 0.0.0.0 (Invalid username [ ]) Disconnected This means the IRC server did not accept the username (User ID) settings in the Ident service (Identd) in mIRC under File/Options/Connect/Identd/. In the error message it shows the part it did not like between the [ ] brackets. Most probably you use characters in your File/ Options/Connect/Identd/User ID settings that the server doesn't like. Make sure you remove all strange characters from your User ID. Remove dots, spaces, and all other non- alphabetical characters.
YOU ARE NOT AUTHORIZED TO USE THIS SERVER
Unable to connect - Connection refused. This means you do not have access to this server. The server has no instructions to let you in (I-line) or it refuses all access for maintenance purposes. Try another server on the same IRC network, preferably a more nearby server, one in your own country or one provided by your own Internet Provider. If you think you should have access to this server contact the administrator of the server and request for an I-Line for the host/IP number that you are trying to connect from.
NO MORE CONNECTIONS ALLOWED IN YOUR CONNECTION CLASS
Connection refused (Max connections at this time) Closing Link (No more connections) This means the maximum number of connections in your class (Y-Line) has been reached. There are too many people from the same company or Internet Provider on this IRC server already. Try another server on the same IRC network, preferably a more nearby server, one in your own country or one provided by your own Internet Provider. If you think you should have access to this server contact the administrator of the server and request for a larger number of allowed connections for the domain that you are trying to connect from.
TOO MANY CONNECTIONS FROM YOUR HOSTNAME
Closing Link (No more connections) Closing Link (You are only allowed one connection from your host.) This means you already have one or more connections to the IRC server and you are not allowed more than the current number of connections from your address or PC. Normally two connections to the same IRC server are allowed. Check and see if you already have a copy of mIRC running with a connection to this server. Also if you are connecting from behind a firewall or proxy (like Internet Connection Sharing) and thus sharing one IP Number, the server will see you all as coming from one address. It will refuse access if more people from your place are on this IRC server already, using the same proxy, or if you have more IRC clients running.
YOU ARE BANNED FROM THIS SERVER
You get this message if you are banned, killed; K-lined. Try another server on the same IRC network, preferably a more nearby server, one in your own country or one provided by your own Internet Provider. Sometimes it is necessary to ban entire domains because abusers connect to the internet via dynamic IP numbers that change and cannot be anticipated. Therefore server admins will ban the entire site/domain, sorry but thats life in a imperfect world. If you feel this is unfair contact the administrator of the server and request for a lift of the K-line on your host, IP number or domain.
SERVER IS FULL
Once a server reaches its maximum user limit, this error occurs. Try another server.
'CONNECTION REFUSED', 'CONNECTION TIMED OUT' or 'UNKNOWN HOST'
The server may not be available or there may be a problem with the DNS entry. Try another server.
YOU HAVEN'T REGISTERED
IP address or local host name is missing/wrong or it is not a public server. Check setup / try another server.
'YOU ARE NOT WELCOMED ON THIS SERVER' or 'GHOSTS NOT ALLOWED..'
You, or your ISP have been banned from the server. Try another server.
CLOSING LINK: K-lined
You do not have access to this server. Try another server.
ERROR : 10049 CANNOT ASSIGN REQUESTED ADDRESS
The DNS entry is invalid. This is most likely because the IRC Network decided to make the server unreachable or out of service (temporal or definitive.) Try another server.
Error : 10051 NETWORK IS UNREACHABLE
There is some comunication problem between your computer and the server (something in the traffic path is telling your PC it can't reach the server.) Check that the address you are trying to connect to is valid. Since it can be a temporal issue, try again later, if it continues, try another server.
Error : 10053 SOFTWARE CAUSED CONNECTION ABORT
This is when the client loses connection with the server, mainly to ping timeouts and glitches on internet connections (Internet is unpredictable, it happens from time to time.) It is a common error. Changing server may help if you get frequent disconnects. On some rare cases, frequent disconnects with this error messages mean a misconfiguration on your computer/home router/ISP.
Error : 10060 CONNECTION TIMED OUT
The connection can't be established. Probably the server is no longer active. Try to update your server lists, or try a different server on the same network. If you are sure that the server exists, and is accepting connections, it means it is busy, and unable to accept more clients. Try another port (6668,6669 are common options.)
Error : 10061 CONNECTION REFUSED
The machine exists, but no IRC server is running there. A common cause is some companies use different machines for IRC and web servers, and you are trying to connect to the one with web server (and no IRC server is running there.) Another posSible cause is the port you selected is not active; you can choose another port to connect (6667 is default, but 6668,6669,7000 are common options). Check the Network's web site, to find the correct port. If you were connected to the server and get this error after a disconnection, its because the IRCD (server program) is down (probably rebooting). Try again in a few minutes, or try another server.
Error : 11001 HOST NOT FOUND
The PC can't find a PC with name you specified. Check the speling of the server you are trying to connect to. It is possible that the server once existed, but it's no longer avalable. Try another server.
Ping Timeout - occurs when a server gets no response from a user's client. Servers periodically "PING" your client. Your client should respond to the server with a "PONG" so that the server knows your client is still connected. When a server does not get the expected response from your client, it disconnects your client.
EOF from client - occurs when, for some reason, a server receives an "EOF" (end of file) message from your client. This is often seen in conjunction with a "Read Error" message.
Read error - occurs when a server can no longer read from a user's client.
Write error - occurs when a server can no longer write to a user's client.
Connection reset by peer - occurs when a server immediately resets the connection of a user who has quit IRC. This enables the user to immediately reconnect without a "ghost" of the user's connection to IRC. (A "ghost" is sometimes a "leftover connection" of a user who was on IRC and quit without the server recognizing that the user's connection has been terminated).
K-lined - occurs when a user is disconnected because an oper added a K: line (kill line) for that user or for another user to whom the disconnected user's address was matched. Kill lines are essentially bans from an IRC server used for severe abuse cases. Another type of ban which would cause a user to disconnect is a G-line.
G-lines are bans from the entire network and are used ONLY in the most severe cases of abuse.
Killed - occurs when a user is disconnected because an oper felt that user was being abusive enough to warrant being "kicked" off the network. When a user is killed, he or she can typically immediately reconnect. A "kill" is sort of like a "slap on the wrist" used for minor abusive issues. Kills are also sometimes used when IRCops (server operators) are joking with each other - or, for example, a "birthday kill" (which has become almost a tradition among IRC operators :)