NAME¶

sc_tbitpmtud — scamper driver to test systems for responsiveness to ICMP packet too big messages

SYNOPSIS¶

DESCRIPTION¶

The sc_tbitpmtud utility provides the ability to connect to a running scamper(1) instance and use that instance to test end systems for their ability to perform Path MTU Discovery, with the output written to a file in warts format. sc_tbitpmtud first tests a given system for responsiveness to ICMP echo packets, and then tests the given system's TCP stack response to ICMP packet too big messages.

The options are as follows:

-?

prints a list of command line options and a synopsis of each.

-a address-file

specifies the name of the input file which consists of a sequence of systems to test, one system per line.

-A ip2as-file

specifies the name of a file which consists of a mapping of prefixes to ASes, one prefix per line.

-c completed-file

specifies the name of a file to record IP addresses that have been tested.

-d dump-id

specifies the dump ID to use to analyze the collected data. Currently, ID values 1 (mssresults) and 2 (asnresults) are valid, which report PMTUD behaviour according to the server's MSS or the server's origin ASN.

-l limit-per-file

specifies the number of tbit objects to record per warts file, before opening a new file and placing new objects.

-m maximum transmission unit

specifies the pseudo maximum transmission unit to use. The available choices are 0, 256, 576, 1280, 1480. If 0 is chosen, sc_tbitpmtud will test each website with all available MTU choices in decreasing size. The default MTU value tested is 1280.

-o output-file

specifies the name of the file to be written. The output file will use the warts format.

-p scamper-port

specifies the port on the local host where scamper(1) is accepting control socket connections.

-r

shuffle the order in which websites are tested.

-t log-file

specifies the name of a file to log progress output from sc_tbitpmtud generated at run time.

-w window-size

specifies the maximum number of tests to conduct in parallel. The window size value depends on the value of the -F parameter passed to the scamper(1) instance.

EXAMPLES¶

Use of this driver requires a scamper(1) instance listening on a port for commands with a configured firewall. The following invocation uses ipfw(8) firewall rules 1 to 100, with a corresponding window size of 100, and an unrestricted packets per second rate, as follows:

To test a set of web servers specified in a file named webservers.txt and formatted as follows:

1,example.com 5063 192.0.2.1 http://www.example.com/


1,example.com 5063 2001:DB8::1 http://www.example.com/


1,example.com 5063 2001:DB8::2 https://www.example.com/

the following command will test all servers for responsiveness to ICMP packet too big messages and record raw data into webservers_00.warts, webservers_01.warts, etc:

The webservers.txt file is required to be formatted as above. The format is: numeric ID to pass to tbit, a label for the webserver, the size of the object to be fetched, the IP address to contact, and the URL to use.

To characterize PMTUD behaviour according to the server's advertised MSS value:

Given files with IPv4 prefixes in prefix2as4.txt and IPv6 prefixes in prefix2as6.txt formatted as follows:

2001:DB8::     48     64496


2001:DB8:1::   48     64497


192.0.2.0      24     64498

the following command will characterize PMTUD behaviour according to the origin ASN of the server:

SEE ALSO¶

scamper(1), sc_wartsdump(1), sc_warts2json(1), warts(5),

M. Luckie and B. Stasiewicz, Measuring Path MTU Discovery Behaviour, Proc. ACM/SIGCOMM Internet Measurement Conference 2010.

A. Medina, M. Allman, and S. Floyd, Measuring Interactions between Transport Protocols and Middleboxes, Proc. ACM/SIGCOMM Internet Measurement Conference 2004.

AUTHORS¶

sc_tbitpmtud was written by Matthew Luckie <mjl@luckie.org.nz>. Ben Stasiewicz contributed an initial implementation of the Path MTU Discovery TBIT test to scamper, building on the work of Medina et al.