--- name: "sc_prefixscan" section: "1" platform: "linux" package: "scamper" version: "20211212-1.2+b1" release: "Debian 13 (Trixie)" platforms: ["linux"] url: "https://new.carta.tech/sc_prefixscan" --- # sc\_prefixscan(1) scamper driver to test if a set of IPv4 links are point-to-point. ## NAME **sc\_prefixscan** – scamper driver to test if a set of IPv4 links are point-to-point. ## SYNOPSIS **sc\_prefixscan** \[**-D**\] \[**-i** *infile*\] \[**-o** *outfile*\] \[**-p** *port*\] \[**-l** *logfile*\] \[**-U** *unix-socket*\] \[**-w** *wait*\] \[**-x** *prefixlen*\] **sc\_prefixscan** \[**-r** *data-file*\] \[**-x** *prefixlen*\] ## DESCRIPTION The **sc\_prefixscan** utility provides the ability to connect to a running [scamper(1)](/scamper/1.md) instance and use it to collect data to infer if an IPv4 link is likely a point-to-point link using the prefixscan method. An address B is the in-bound interface of a router in a traceroute path if we find an alias A' of the address A returned for the previous hop and A' is a /31 or /30 mate of B, i.e. the link between A and B is a point-to-point link. The prefixscan method infers A and A' are aliases if the IPIDs in responses to five alternating probes sent one second apart monotonically increase and differ by no more than 1,000, or probes to A and A' elicit responses with a common source address. The first technique is a pairwise comparison similar to Ally, and the second is the Mercator technique. The supported options to **sc\_prefixscan** are as follows: - **-D** causes **sc\_prefixscan** to detach and become a daemon. - **-i** *infile* specifies a file containing a list of IPv4 address pairs adjacent in traceroute paths to test if they are point-to-point links. - **-o** *outfile* specifies the name of the output file to be written during the data collection phase. The output file will use the warts(5) format. - **-p** *port* specifies the port on the local host where [scamper(1)](/scamper/1.md) is accepting control socket connections. - **-l** *logfile* specifies the name of a file to log progress output from **sc\_prefixscan** generated at run time. - **-r** *data-file* specifies the name of the data file to be parsed for point-to-point link inferences that were collected by **sc\_prefixscan** in a previous data collection. - **-U** *unix-socket* specifies the name of a unix domain socket where a local [scamper(1)](/scamper/1.md) instance is accepting control socket connections. - **-w** *wait* specifies the length of time in seconds to wait between probing the same IPv4 address with different methods. By default, **sc\_prefixscan** waits five seconds between methods. - **-x** *prefixlen* specifies the maximum size of prefix to consider. By default, **sc\_prefixscan** considers up to an IPv4 /30 prefix. ## EXAMPLES Given a traceroute with the following path: ``` traceroute to 192.0.30.64 ``` ``` 1 192.0.2.1 ``` ``` 2 192.0.32.10 ``` ``` 3 192.0.31.8 ``` ``` 4 192.0.30.64 ``` then to collect data to infer if the implied IPv4 links are point-to-point, put the links in a file named infile.txt formatted as follows: ``` 192.0.2.1 192.0.32.10 ``` ``` 192.0.32.10 192.0.31.8 ``` ``` 192.0.31.8 192.0.30.64 ``` and use a [scamper(1)](/scamper/1.md) daemon listening on port 31337 using: ``` sc_prefixscan -i infile.txt -o outfile.warts -p 31337 ``` To obtain the inferred point-to-point links from outfile.warts: ``` sc_prefixscan -r outfile.warts ``` ## SEE ALSO [scamper(1)](/scamper/1.md), [sc\_ally(1)](/sc_ally/1.md), [sc\_ipiddump(1)](/sc_ipiddump/1.md), [sc\_wartsdump(1)](/sc_wartsdump/1.md), [sc\_warts2text(1)](/sc_warts2text/1.md), [sc\_warts2json(1)](/sc_warts2json/1.md), M. Luckie and k. claffy, *A Second Look at Detecting Third-party Addresses in Traceroute Traces with the IP Timestamp Option*, Proc. Passive and Active Measurement Conference 2014. R. Govindan and H. Tangmunarunkit, *Heuristics for Internet Map Discovery*, Proc. IEEE INFOCOM 2000. N. Spring, R. Mahajan, and D. Wetherall, *Measuring ISP topologies with Rocketfuel*, Proc. ACM SIGCOMM 2002. ## AUTHORS **sc\_prefixscan** was written by Matthew Luckie \.