Home page logo
/
Intro Reference Guide Book Install Guide
Download Changelog Zenmap GUI Docs
Bug Reports OS Detection Propaganda Related Projects
In the Movies In the News

File path-mtu

Script types: hostrule
Categories: safe, discovery
Download: http://nmap.org/svn/scripts/path-mtu.nse

User Summary

Performs simple Path MTU Discovery to target hosts.

TCP or UDP packets are sent to the host with the DF (don't fragment) bit set and with varying amounts of data. If an ICMP Fragmentation Needed is received, or no reply is received after retransmissions, the amount of data is lowered and another packet is sent. This continues until (assuming no errors occur) a reply from the final host is received, indicating the packet reached the host without being fragmented.

Not all MTUs are attempted so as to not expend too much time or network resources. Currently the relatively short list of MTUs to try contains the plateau values from Table 7-1 in RFC 1191, "Path MTU Discovery". Using these values significantly cuts down the MTU search space. On top of that, this list is rarely traversed in whole because: * the MTU of the outgoing interface is used as a starting point, and * we can jump down the list when an intermediate router sending a "can't fragment" message includes its next hop MTU (as described in RFC 1191 and required by RFC 1812)

Example Usage

nmap --script path-mtu target

Script Output

Host script results:
|_path-mtu: 1492 <= PMTU < 1500

Host script results:
|_path-mtu: PMTU == 1006

Requires


Author: Kris Katterjohn

License: Same as Nmap--See http://nmap.org/book/man-legal.html

Nmap Site Navigation

Intro Reference Guide Book Install Guide
Download Changelog Zenmap GUI Docs
Bug Reports OS Detection Propaganda Related Projects
In the Movies In the News
[ Nmap | Sec Tools | Mailing Lists | Site News | About/Contact | Advertising | Privacy ]