Zline

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On IRCds such as UnrealIRCd, Zline (sometimes written as Z-line or Z:Line) is an IRC-related term. It refers to banning a client from an IRC-network (this can be for a set amount of time or indefinitely). Z-lines - originally Z:Lines - are sometimes stored in the configuration file of the IRCd(s), although some networks, who handle lines through the services, prefer to have them stored in the services' configuration files. Modern IRC daemons will also allow IRC Operators to set these lines during normal operation, where access to the server configuration file is not routinely needed. Whenever a Z-lined person attempts to connect to the IRC-network, the IRC daemon will automatically and immediately close the socket to the client, often displaying a message explaining the reasoning behind the ban.

Zlines are a "newer" version of K-lines. Most Z-lines are "awarded" to people who abuse the network as a whole (on smaller networks, these are more frequently issued for isolated incidents). K-line is an abbreviation for "kill line," and Zline for "zap line."

One advantage to using Zlines over Klines/Glines, from a server/network administrator's perspective, is that a Zline uses less bandwidth than a Kline, mainly because it doesn't wait for an ident response or DNS traversal, as described below.

A disadvantage to using Zline over Kline/Gline is that it becomes more difficult to ban entire ISPs and very dynamic IP addresses, common with some dialup and DSL connections. For example, if a network administrator wants to ban all of ISP example.com (with hypothetical IP address ranges of 68.0.0.0 - 68.255.255.255 and 37.0.0.0 - 38.255.255.255), a Gline regex could be *@*example.com, whereas Zline would require *@37.*.*.*, *@38.*.*.*, and *@68.*.*.* to accomplish the same thing.

Zlines also work differently than Klines. Zlines are typically set as *@IP or *@host, with the first being the best option. Zlines do not wait for an ident response from the connecting user, but immediately close the socket once the user's IP is compared to the Zline list and a match is found. If the *@host option is used, the server must conduct a reverse DNS lookup on the user and then compare the returned host to the hosts in the Zline list. This can result in delays, or if the DNS doesn't return correctly, banned users could still get on the network. In actuality, the *@host option is completely against the intentions of using a Zline, and therefore some IRCd programs will not allow anything other than *@IP, with wildcards (?,*) allowed in the IP section to block entire subnets.

Zlines can also be global, in which case they are called GZlines. GZlines work in the same manner as Zlines, except that they propagate to every server on the network.

Another difference from K:Line is that: If some IP is banned, nothing, even other servers, can connect from this IP (or IP range, depending on the regex). K:Line affects only IRC clients, and not servers.

Not all IRCds are the same and therefore not all of them support Zlines. Other IRCds, such as Charybdis, use an Xline instead.