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diff --git a/doc/ipv6.html b/doc/ipv6.html new file mode 100644 index 00000000..f5a049c5 --- /dev/null +++ b/doc/ipv6.html @@ -0,0 +1,48 @@ +<html> +<head> +<title>Notes on IPv6 Handling in Rsyslog</title> +</head> +<body> +<h1>Notes on IPv6 Handling in Rsyslog</h1> +<p><b>Rsyslog fully* supports sending and receiving syslog messages via both +IPv4 and IPv6.</b> IPv6 is natively supported for both UDP and TCP. However, +there are some options that control handling of IPv6 operations. I thought it is +is a good idea to elaborate a little about them, so that you can probably find +your way somewhat easier.</p> +<p>First of all, you can restrict rsyslog to using IPv4 or IPv6 addresses only +by specifying the -4 or -6 command line option (now guess which one does +what...). If you do not provide any command line option, rsyslog uses IPv4 and +IPv6 adresses concurrently. In practice, that means the listener binds to both +addresses (provided they are configured). When sending syslog messages, rsyslog +uses IPv4 addresses when the receiver can be reached via IPv4 and IPv6 addresses +if it can be reached via IPv6. If it can be reached on either IPv4 and v6, +rsyslog leaves the choice to the socket layer. The important point to know is +that it uses whatever connectivity is available to reach the destination.</p> +<p><b>There is one subtle difference between UDP and TCP.</b> With the new +IPv4/v6 ignorant code, rsyslog has potentially different ways to reach +destinations. The socket layer returns all of these pathes in a sorted array. +For TCP, rsyslog loops through this array until a successful TCP connect can be +made. If that happens, the other addresses are ignored and messages are sent via +the succesfully-connected socket.</p> +<p>For UDP, there is no such definite success indicator. Sure, the socket layer +may detect some errors, but it may not notice other errors (due to the +unreliable nature of UDP). By default, the UDP sender also tries one entry after +the other in the sorted array of destination addresses. When a send fails, the +next address is tried. When the send function finally succeeds, rsyslogd assumes +the UDP packet has reached its final destination. However, if rsyslogd is +started with the "-A" (capital A!) was given on the command line, rsyslogd will +continue to send messages until the end of the destination address array is +reached. This may result in duplicate messages, but it also provides some +additional reliability in case a message could not be received. You need to be +sure about the implications before applying this option. In general, it is NOT +recommended to use the -A option.</p> +<p><i><b>*</b>rsyslog does not support RFC 3195 over IPv6. The reason is that +the RFC 3195 library, <a href="http://www.liblogging.org/">liblogging</a>, +supports IPv4, only. Currently, there are no plans to update either rsyslog to +another RFC 3195 stack or update liblogging. There is simply no demand for 3195 +solutions.</i></p> +<p><font size="2">Last Updated: 2007-07-02<br> +Copyright © 2007 by Rainer Gerhards, released under the GNU GPL V2 or later.</font></p> + +</body> +</html> |