Editing IRCd (section)

=== Z-line {{anchor|GZ-line|D-line|X-line}} ===
{{Redirect|Zline||Z-line (disambiguation){{!}}Z-line}}
A '''Z-line''' or '''zap line''' (also written '''Z:line''') is similar to a K-line, but applied to a client's IP address range, and is considered to be used in extreme cases. Because a Z-line does not have to check usernames (identd) or ''resolved'' hostnames, it can be applied to a user before they send any data at all upon connection. Therefore, a Z-line is more efficient and uses fewer resources than a K-line or G-line when banning large numbers of users.

In some IRC daemons such as ircd-hybrid, this is called a '''D-line''' (deny line) or an '''X-line'''.

Z-lines are sometimes stored in the configuration file of the IRCd, although some networks, who handle lines through the IRC services, prefer to have them stored in their service's configuration files. Whenever a Z-lined person attempts to connect to the IRC network, either the services or the IRC daemon will automatically disconnect the client, often displaying a message explaining the reasoning behind the ban.

Z-lines are a variant of K-lines, which work in much the same way. 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).

Z-lines also work slightly differently from K-lines. Z-lines are typically set as *@IP or *@host, with the first being the better option. Z-lines 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 Z-line 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 Z-line 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 Z-line, and therefore some IRCd programs will not allow anything other than *@IP, with [[wildcard character|wildcards]] (?,*) or [[Classless Inter-Domain Routing|CIDR prefix lengths]] (''e.g. /8)'' allowed in the IP section to block entire subnets. Another difference from K-lines (which affect only IRC clients) is if an IP is banned, nothing, not even other servers, can connect from this IP (or IP range, depending on the banmask).

One advantage to using Z-lines over K-lines and G-lines, from a server or network administrator's perspective, a Z-line uses less bandwidth than a K-line, mainly because it doesn't wait for an [[ident protocol|ident]] response or [[Domain Name System|DNS]] lookup.

A disadvantage to using Z-line over K-line or G-line is that it becomes more difficult to ban entire ISPs and very dynamic IP addresses, common with some [[dialup]] and [[Digital subscriber line|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 G-line could use *@*example.com, whereas Z-line would require *@37.*.*.*, *@38.*.*.*, and *@68.*.*.* to accomplish the same thing.

Z-lines can also be global, in which case they are called '''GZ-lines'''. GZ-lines work in the same manner as Z-lines, except that they propagate to every server on the network. Some IRC daemons may also be configured to share Z-lines with other servers.