-
.. role:: example-rule-emphasis
IP Keywords
The ttl keyword is used to check for a specific IP time-to-live value
in the header of a packet. The format is::
- ttl:<number>
+ ttl:<number>;
For example::
want to match. The Time-to-live value determines the maximal amount
of time a packet can be in the Internet-system. If this field is set
to 0, then the packet has to be destroyed. The time-to-live is based
-on hop count. Each hop/router the packet passes subtracts one of the
+on hop count. Each hop/router the packet passes subtracts one from the
packet TTL counter. The purpose of this mechanism is to limit the
existence of packets so that packets can not end up in infinite
routing loops.
.. container:: example-rule
- alert ip $EXTERNAL_NET any -> $HOME_NET any (msg:"GPL MISC 0 ttl"; :example-rule-emphasis:`ttl:0;` reference:url,support.microsoft.com/default.aspx?scid=kb#-#-EN-US#-#-q138268; reference:url,www.isi.edu/in-notes/rfc1122.txt; classtype:misc-activity; sid:2101321; rev:9;)
+ alert ip $EXTERNAL_NET any -> $HOME_NET any (msg:"IP Packet With TTL 0";
+ :example-rule-emphasis:`ttl:0;` classtype:misc-activity; sid:1; rev:1;)
ipopts
^^^^^^