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ICMPError Element Documentation


ICMPError -- Click element; generates ICMP error packets



Ports: 1 input, 1 output
Processing: agnostic
Package: icmp (core)


Generate an ICMP error packet, with specified TYPE and CODE, in response to an incoming IP packet. The output is an IP/ICMP packet. The ICMP packet's IP source address is set to SRC. The error packet will include (as payload) the original packet's IP header and an initial segment of its IP payload. ICMPError sets the packet destination IP annotation and, optionally, the fix_ip_src annotation. TYPE and CODE may be integers between 0 and 255 or mnemonic names; CODE defaults to 0. Valid named TYPEs are `unreachable' [3], `sourcequench' [4], `redirect' [5], `timeexceeded' [11], and `parameterproblem' [12]. Valid named CODEs are `net' [0], `host' [1], `protocol' [2], `port' [3], and `needfrag' [4] for `unreachable'; `net' [0] and `host' [1] for `redirect'; `transit' [0] and `reassembly' [1] for `timeexceeded'; and `erroratptr' [0], `missingopt' [1], and `length' [2] for `parameterproblem'. The intent is that elements that give rise to errors, like DecIPTTL, should have two outputs, one of which is connected to an ICMPError. Perhaps the ICMPError should be followed by a rate limiting element. ICMPError never generates a packet in response to an ICMP error packet, a fragment, or a link broadcast. The BADADDRS keyword argument supplies an optional list of bad IP addresses; if it is present, then ICMPError doesn't generate packets in response to packets with one of those addresses as either source or destination. The output of ICMPError should be connected to the routing lookup machinery, much as if the ICMP errors came from a hardware interface. If TYPE is 12 (`parameterproblem') and CODE is 0 (`erroratptr'), ICMPError takes the error pointer from the packet's ICMP parameter problem annotation. The IPGWOptions element sets the annotation. If TYPE is 5 (`redirect'), produces an ICMP redirect message. The gateway address is taken from the destination annotation. Usually a Paint-PaintTee element pair hands the packet to a redirect ICMPError. RFC1812 says only code 1 (`host') should be used. If TYPE is 3 ('unreachable') and CODE is 4 ('needfrag'), produces an ICMP unreachable message containing the MTU of the next-hop interface, specified by the PMTU keyword. This error should be returned to the sender of an IP packet with the DF bit set, that is longer than the next-hop MTU, to support Path MTU Discovery. If the input packet has a source route option, the output packet will also have a source route option, containing the routers from the input source route, reversed. Will not generate a packet larger than MTU, which defaults to 576. Keyword arguments are:

A list of source IP addresses for which ICMP errors should not be generated. Usually the limited broadcast address(es) of the current subnet.
Unsigned. The maximum error packet size generated. Defaults to 576.
Unsigned. The maximum MTU for the path, reported in unreachable messages.
Boolean. If false, do not set the fix_ip_src annotation on output packets. Defaults to true.


This configuration fragment produces ICMP Time Exceeded error messages in response to TTL expirations, but limits the rate at which such messages can be sent to 10 per second:

 dt : DecIPTTL;
 dt[1] -> ICMPError(, timeexceeded) -> m :: RatedSplitter(10) -> ...
 m[1] -> Discard;


ICMPError can't decide if the packet's source or destination address is an IP directed broadcast address; it is supposed to ignore packets with such addresses.


DecIPTTL, FixIPSrc, IPGWOptions

Generated by 'click-elem2man' from '../elements/icmp/icmperror.hh:6' on 12/Jul/2011.


elements/icmperror.txt · Last modified: 2011/07/12 11:29 (external edit)
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