NAME

scamper —

parallel Internet measurement utility

SYNOPSIS

scamper [-?Dv] [-c command] [-p pps] [-w window] [-M monitorname] [-l listname] [-L listid] [-C cycleid] [-o outfile] [-F firewall] [-n nameserver] [-d debugfile] [-e pidfile] [-O options] [-i IPs | -I cmds | -f file | -P [ip:]port | -R name:port | -U unix-dom]

DESCRIPTION

The scamper utility provides the ability to execute Internet measurement techniques to IPv4 and IPv6 addresses, in parallel, to fill a specified packets-per-second rate. Currently, scamper supports the well-known traceroute and ping techniques, DNS, as well as MDA traceroute, alias resolution, some parts of tbit, sting, and neighbour discovery.

scamper has five modes of operation. First, scamper can be supplied a list of one or more addresses on the command line with the -i option. scamper will then execute a command with each of the supplied addresses, in parallel, and output the results as each task completes. Second, scamper can be supplied a list of one or more addresses in a listfile, one address per line, using the -f option. Third, scamper can be supplied a list of one or more complete commands on the command line with the -I option. Fourth, scamper can be instructed to listen on an IP address and port specified with the -P option, or on a unix domain socket specified with the -U option, where it can take commands dynamically. Finally, scamper can be instructed to connect to a remote host and port specified with the -R option, where it will be supplied with commands dynamically.

For most modules, scamper must be run as root.

The options are as follows:

-?

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

-v

causes scamper to output version information and exit.

-D

With this option set, scamper will detach and become a daemon. Use with the -P or -U options.

-c command

specifies the command for scamper to use by default. The current choices for this option are:

dealias: use Ally, Mercator, or Radargun-style probing to infer which IP addresses belong to the same system.
host: issue simple DNS queries to a domain name server.
neighbourdisc: issue an IPv4 ARP or IPv6 Neighbour discovery query to determine the layer-2 address of an IP address on the same network.
ping: conduct simple delay measurements with various probe types.
trace: conduct classic and Paris-style traceroute probing, which infers a single path towards a destination.
tracelb: use the multipath discovery algorithm (MDA) to infer the presence of load-balanced paths towards a destination.
sniff: capture a subset of packets arriving at the host using a subset of tcpdump-style filter expressions.
sting: use the sting method to infer one-way packet loss with a TCP receiver.
tbit: use techniques from the TCP behavior inference tool (TBIT) to infer properties of a TCP receiver.

scamper uses trace by default. The options for each of these commands are documented in their own sections of this manual page.

-p pps

specifies the target packets-per-second rate for scamper to reach. By default, this value is 20.

-w window

specifies the maximum number of tasks that may be probed in parallel. A value of zero places no upper limit. By default, zero is used.

-M monitorname

specifies the canonical name of machine where scamper is run. This value is used when recording the output in a warts output file.

-l listname

specifies the name of the list when run from the command line. This value is used when recording the output in a warts output file.

-L listid

specifies the numerical id of the list when run from the command line. This value is used when recording the output in a warts output file.

-C cycleid

specifies the numerical cycle id to begin with when run from the command line. This value is used when recording the output in a warts output file.

-o outfile

specifies the default output file to write measurement results to. By default, stdout is used.

-F firewall

specifies that scamper may use the firewall in measurements that require it (tbit and sting). scamper supports two firewall types: IPFW, and PF. To use the IPFW firewall, pass ipfw:<start>-<end>, where <start> is the first rule scamper can use, and <end> is the last. To use the PF firewall, pass pf:<anchor>:<num>, where <anchor> is the anchor for scamper to use, and <num> specifies the number of rules scamper is allowed to use.

-n nameserver

specifies the nameserver for scamper to use. By default, scamper uses the first nameserver specified in /etc/resolv.conf

-d debugfile

specifies a filename to write debugging messages to. By default, no debugfile is used, though debugging output is sent to stderr if scamper is built for debugging.

-e pidfile

specifies a file to write scamper's process ID to. If scamper is built with privilege separation, the ID of the unprivileged process is written.

-O options

allows scamper's behaviour to be further tailored. The options are case insensitive. The current choices for this option are:

text: output results in plain text. Suitable for interactive use.
warts: output results in warts format. Suitable for archiving measurement results and for use by researchers as it records details that cannot be easily represented with the text option.
json: output results in json format. Suitable for processing measurement results with a scripting language. A better approach is to output results in warts format, and to use sc_warts2json(1).
planetlab: tell scamper it is running on a planetlab system. Necessary to use planetlab's safe raw sockets.
rawtcp: tell scamper to use IPPROTO_RAW socket to send IPv4 TCP probes, rather than a datalink socket.
ICMP-rxerr: tell scamper to use IP_RECVERR or IPV6_RECVERR to receive ICMP responses, rather than raw sockets. This is useful on Linux systems that have these sockets, and scamper does not have the permissions to obtain a raw socket. This option currently only works with the trace command.
select: tell scamper to use select(2) rather than poll(2)
kqueue: tell scamper to use kqueue(2) rather than poll(2) on systems where kqueue(2) is available.
epoll: tell scamper to use epoll(7) rather than poll(2) on systems where epoll(7) is available.
tsps: the input file consists of a sequence of IP addresses for pre-specified IP timestamps.
cmdfile: the input file consists of complete commands.
noinitndc: do not initialise the neighbour discovery cache.
outcopy: write a copy of all data written by scamper with the default output method.
debugfileappend: append to the debugfile specified with the -d option. The default is to truncate the debugfile.
notls-remote: do not use TLS when establishing a connection with the remove controller specified with the -R option.
notls: do not use TLS anywhere in scamper, including tbit.

-i IP 1..N

specifies a list of one or more addresses to probe, on the command line, using the command specified with the -c option.

-f listfile

specifies the input file to read for target addresses, one per line, and uses the command specified with the -c option on each.

-I cmds

specifies a list of one or more complete commands, including target addresses, for scamper to execute.

-P [ip:]port

specifies that scamper provide a control socket listening on the specified IP address and port on the local host. If an IP address is not specified, scamper will bind to the port specified on the loopback address.

-R name:port

specifies that scamper connects to a specified remote host and port to receive commands.

-U unix domain socket

specifies that scamper provide a control socket listening on the specified socket in the unix domain.

TRACE OPTIONS

The trace command is used for conducting classic and Paris-style traceroute probing, which infers a single path towards a destination. The following variations of the traceroute(8) options are available:

trace [-MQT] [-c confidence] [-d dport] [-f firsthop] [-g gaplimit] [-G gapaction] [-l loops] [-m maxttl] [-N squeries] [-o offset] [-O option] [-p payload] [-P method] [-q attempts] [-r rtraddr] [-s sport] [-S srcaddr] [-t tos] [-U userid] [-w wait] [-W wait-probe] [-z gss-entry] [-Z lss-name]

-c confidence

specifies that a hop should be probed to a specified confidence level (95% or 99%) to be sure the trace has seen all interfaces that will reply for that hop.

-d dport

specifies the base destination port value to use for UDP-based and TCP-based traceroute methods. For ICMP-Paris, this option sets the ICMP checksum value.

-f firsthop

specifies the TTL or HLIM value to begin probing with. By default, a first hop of one is used.

-g gaplimit

specifies the number of unresponsive hops permitted until a check is made to see if the destination will respond. By default, a gap limit of 5 hops is used. Setting the gap limit to 0 disables the gap limit, but doing this is not recommended.

-G gapaction

specifies what should happen if the gaplimit condition is met. A value of 1 (default) means halt probing, while a value of 2 means send last-ditch probes.

-l loops

specifies the maximum number of loops permitted until probing stops. By default, a value of one is used. A value of zero disables loop checking.

-m maxttl

specifies the maximum TTL or HLIM value that will be probed. By default, there is no restriction, apart from the 255 hops that the Internet protocols allow.

-M

specifies that path MTU discovery (PMTUD) should be attempted for the path when the initial traceroute completes. scamper will not conduct PMTUD unless it is probing a responsive destination, as otherwise there is no way to distinguish all packets being lost from just big packets (larger than MTU) being lost.

-N squeries

specifies the number of consecutive hops that may have an outstanding probe. By default, only one hop may have an outstanding probe. Increasing the number of outstanding probes will allow traceroutes to complete faster, at the expense of sending unnecessary probes. The number of outstanding probes must be less than the gaplimit.

-o offset

specifies the fragmentation offset to use in probes. By default, no offset is used.

-O option

specifies optional arguments to use. The current choices for this option are:

dl: specifies that the datalink socket should be used to timestamp packets, and to receive certain packets.
dtree-noback: specifies that the traceroute should not do backwards probing when using doubletree.
ptr: lookup hostnames for intermediate traceroute hops.

-p payload

specifies the payload of the probe to use as a base. The payload is specified in hexadecimal. Note that the payload supplied is merely a base; the first 2 bytes may be modified to accomplish ICMP-Paris and UDP-Paris traceroute.

-P method

specifies the traceroute method to use. scamper currently supports five different probe methods: UDP, ICMP, UDP-Paris, ICMP-Paris, TCP, and TCP-ACK. Note: scamper uses UDP-Paris by default, and these options are case insensitive.

-q attempts

specifies the maximum number of attempts to obtain a response per hop. By default, a value of two is used.

-Q

specifies that all allocated probes are sent, regardless of how many responses have been received.

-r rtraddr

specifies the IP address of the router to use.

-s sport

specifies the source port value to use. For ICMP-based methods, this option specifies the ICMP identifier to use.

-S srcaddr

specifies the source address to use in probes. The address cannot be spoofed.

-t tos

specifies the value to set in the IP ToS/DSCP + ECN byte. By default, this byte is set to zero.

-T

specifies that time exceeded messages from the destination do not cause the trace to be defined as reaching the destination.

-U userid

specifies an unsigned integer to include with the data collected; the meaning of the user-id is entirely up to the user and has no effect on the behaviour of traceroute.

-w wait

specifies how long to wait, in seconds, for a reply. By default, a value of 5 is used.

-W wait-probe

specifies the minimum time to wait, in 10s of milliseconds, between sending consecutive probes. By default the next probe is sent as soon as possible.

-z gss-entry

specifies an IP address to halt probing when encountered; used with the double-tree algorithm.

-Z lss-name

specifies the name of the local stop set to use when determining when to halt probing backwards; used with the double-tree algorithm.

PING OPTIONS

The ping command is used for conducting simple delay measurements with various probe types. The following variations of the ping(8) options are available:

ping [-R] [-A TCP-ack] [-B payload] [-c probecount] [-C ICMP-sum] [-d dport] [-F sport] [-i wait] [-m ttl] [-M MTU] [-o replycount] [-O options] [-p pattern] [-P method] [-r rtraddr] [-s size] [-S srcaddr] [-T timestamp] [-U userid] [-W timeout] [-z tos]

-A TCP-ack

specifies the number to use in the acknowledgement field of the TCP header, or the sequence number field of the TCP header when sending reset probes.

-B payload

specifies, in a hexadecimal string, the payload to include in each probe.

-c probecount

specifies the number of probes to send before exiting. By default, a value of 4 is used.

-C ICMP-sum

specifies the ICMP checksum to use when sending a probe. The payload of each probe will be manipulated so that the checksum is valid.

-d dport

specifies the destination port to use in each TCP/UDP probe, and the first ICMP sequence number to use in ICMP probes.

-F sport

specifies the source port to use in each TCP/UDP probe, and the ICMP ID to use in ICMP probes.

-i wait

specifies the length of time to wait, in seconds, between probes. By default, a value of 1 is used.

-m ttl

specifies the TTL value to use for outgoing packets. By default, a value of 64 is used.

-M MTU

specifies a pseudo MTU value. If the response packet is larger than the pseudo MTU, an ICMP packet too big (PTB) message is sent.

-o replycount

specifies the number of replies required at which time probing may cease. By default, all probes are sent.

-O options

The current choices for this option are:

dl: specifies that the ping should use datalink sockets, rather than raw sockets.
nosrc: specifies that the real address of the host should not be embedded in the payload of the packet when the spoof option is used.
spoof: specifies that the source address is to be spoofed according to the address specified with the -S option. The address scamper would otherwise use as the source address is embedded in the payload of the probe unless the nosrc option is used.
tbt: specifies that the goal of the ping is to obtain fragmented responses, so that the -c option specifies how many packets to send, and the -o option specifies how many fragmented responses are desired.

-p pattern

specifies the pattern, in hex, to use in probes. Up to 16 bytes may be specified. By default, each probe's bytes are zeroed.

-P method

specifies the type of ping packets to send. By default, ICMP echo requests are sent. Choices are: ICMP-echo, ICMP-time, TCP-syn, TCP-ack, TCP-ack-sport, TCP-synack, TCP-rst, UDP, and UDP-dport, and these options are case insensitive.

-r rtraddr

specifies the IP address of the router to use.

-R

specifies that the record route IP option should be used.

-s size

specifies the size of the probes to send. The probe size includes the length of the IP and ICMP headers. By default, a probe size of 84 bytes is used for IPv4 pings, and 56 bytes for IPv6 pings.

-S srcaddr

specifies the source address to use in probes. The address can be spoofed if -O spoof is included.

-T timestamp

specifies that an IP timestamp option be included. The timestamp option can either be: tsprespec where IP addresses of devices of interest can be specified; tsonly, where timestamps are embedded by devices but no IP addresses are included; and tsandaddr, where timestamps and IP addresses are included by devices in the path. See the examples section for more information.

-U userid

specifies an unsigned integer to include with the data collected; the meaning of the user-id is entirely up to the user and has no effect on the behaviour of ping.

-W timeout

specifies how long to wait for responses after the last ping is sent. By default this is one second.

-z tos

specifies the value to use in the IPv4 ToS/DSCP + ECN byte. By default, this byte is set to zero.

DEALIAS OPTIONS

The dealias command is used to send probes for the purpose of alias resolution. It supports the mercator technique, where aliases are inferred if a router uses a different address when sending an ICMP response; the ally technique, where aliases are inferred if a sequence of probes sent to alternating IP addresses yields responses with incrementing, interleaved IP-ID values; radargun, where probes are sent to a set of IP addresses in multiple rounds and aliases are inferred by post-processing the results; prefixscan, where an alias is searched in a prefix for a specified IP address; and bump, where two addresses believed to be aliases are probed in an effort to force their IP-ID values out of sequence. The following options are available for the scamper dealias command:

dealias [-d dport] [-f fudge] [-m method] [-o replyc] [-O option] [-p probe-options] [-q attempts] [-r wait-round] [-s sport] [-t ttl] [-U userid] [-w wait-timeout] [-W wait-probe] [-x exclude]

-d dport

specifies the destination port to use when sending probes. Only valid for the mercator technique; destination ports can be specified in probedefs defined with -p for other alias resolution methods.

-f fudge

specifies a fudge factor for alias matching. Defaults to 200. Only valid for ally and bump.

-m method

specifies which method to use for alias resolution. Valid options are: ally, bump, mercator, prefixscan, and radargun, and these options are case insensitive.

-o replyc

specifies how many replies to wait for. Only valid for prefixscan.

-O option

allows alias resolution behaviour to be further tailored. The current choices for this option are:

inseq: where IP-ID values are required to be strictly in sequence (with no tolerance for packet reordering)
shuffle: randomise the order of probes sent each round; only valid for radargun probing.
nobs: do not allow for byte swapped IP-ID values in responses. Valid for ally and prefixscan.

-p probedef

specifies a definition for a probe. Possible options are:

-c sum: specifies what ICMP checksum to use for ICMP probes. The payload of the probe will be altered appropriately.
-d dst-port: specifies the destination port of the probe. Defaults to 33435.
-F src-port: specifies the source port of the probe. Defaults to (pid & 0x7fff) + 0x8000.
-i IP: specifies the destination IP address of the probe.
-M mtu: specifies the pseudo MTU to use when soliciting fragmented responses.
-P method: specifies which method to use for the probe. Valid options are: UDP, UDP-dport, TCP-ack, TCP-ack-sport, TCP-syn-sport, and ICMP-echo, and these options are case insensitive.
-s size: specifies the size of the probes to send.
-t ttl: specifies the IP time to live of the probe.

The ally method accepts up to two probe definitions; the prefixscan method expects one probe definition; radargun expects at least one probe definition; bump expects two probe definitions.

-q attempts

specifies how many times a probe should be retried if it does not obtain a useful response.

-r wait-round

specifies how many milliseconds to wait between probing rounds with radargun.

-s sport

specifies the source port to use when sending probes. Only valid for mercator.

-t ttl

specifies the time-to-live of probes sent. Only valid for mercator.

-U userid

specifies an unsigned integer to include with the data collected; the meaning of the user-id is entirely up to the user and has no effect on the behaviour of dealias.

-w wait-timeout

specifies how long to wait in seconds for a reply from the remote host.

-W wait-probe

specifies how long to wait in milliseconds between probes.

-x exclude

specifies an IP address to exclude when using the prefixscan method. May be specified multiple times to exclude multiple addresses.

HOST OPTIONS

The host command can issue requests to a domain name server. The following options are available for the scamper host command:

host [-r] [-R retry-count] [-s server-ip] [-t type] [-U userid] [-W wait]

-r: specifies that this query is a non-recursive query. The default is to issue a recursive query.
-R retry-count: specifies the number of retries. The default is to send one retry.
-s server-ip: specifies the IP address of the name server to query instead of the default nameserver.
-t type: specifies the DNS query type. The type argument can be one of the following: A, AAAA, PTR, and MX. The default is A if a name is queried, or a PTR if an IP address is queried.
-U userid: specifies an unsigned integer to include with the data collected; the meaning of the user-id is entirely up to the user and has no effect on the behaviour of host.
-W wait: specifies the number of seconds to wait for a response. The default is to wait for five seconds.

NEIGHBOUR DISCOVERY OPTIONS

The neighbourdisc command attempts to find the layer-2 address of a given IP address using IPv4 ARP or IPv6 Neighbour Discovery. The following options are available for the scamper neighbourdisc command:

neighbourdisc [-FQ] [-i interface] [-o reply-count] [-q attempts] [-w wait]

-F: specifies that we only want the first response.
-Q: specifies that we want to send all attempts.
-i interface: specifies the name of the interface to use for neighbour discovery.
-o reply-count: specifies how many replies we wait for.
-q attempts: specifies how many probes we send out.
-w wait: specifies how long to wait between probes in milliseconds. Defaults to 1000.

TBIT OPTIONS

The tbit command can be used to infer TCP behaviour of a specified host. At present, it implements tests to check the ability of the host to respond to ICMP Packet Too Big messages, respond to Explicit Congestion Notification, test Selective Acknowledgement behaviour, the Initial Congestion Window, and resilience to Blind Attacks. The following options are available for the scamper tbit command:

tbit [-t type] [-p app] [-d dport] [-s sport] [-a acks] [-b ASN] [-i ICW] [-f cookie] [-L limit] [-m mss] [-M mtu] [-o offset] [-O option] [-P ptbsrc] [-q attempts] [-S srcaddr] [-T ttl] [-u url] [-U userid] [-w wscale]

-t type

specifies which type of testing to use. Valid options are: pmtud, ecn, null, sack-rcvr, icw, abc, blind-rst, blind-syn, blind-data.

-p app

specifies what kind of traffic to generate for testing. Destination port defaults the application standard port. Valid applications are: http, bgp.

-d dport

specifies the destination port for the packets being sent. Defaults are application-specific.

-s sport

specifies the source port for the packets being sent. Default is based of the scamper process id.

-a acks

specifies the sequence of packets that should be acknowledged as part of the ABC test.

-b ASN

specifies the autonomous system number (ASN) that should be used when establishing a BGP session.

-i ICW

specifies the initial congestion window (ICW) that we expect from the peer when conducting the ABC test.

-f cookie

specifies the TCP fast open cookie that should be used when establishing a TCP connection.

-L limit

test the response to a theoretical limit (L) value with ABC.

-m mss

specifies the maximum segment size to advertise to the remote host.

-M mtu

specifies the MTU to use in a Packet Too Big message.

-o offset

specifies the sequence number offset to use when conducting blind-syn and blind-rst tests, and the acknowledgement number offset to use when conducting a blind-data test.

-O option

allows tbit behaviour to be further tailored. The current choices for this option are:

blackhole: for PMTUD testing, do not send Packet Too Big messages; this tests to ability of a host to infer a PMTUD blackhole and work around it.
tcpts: advertise support for TCP timestamps when establishing a TCP connection. If the peer supports TCP timestamps, embed timestamps in data packets.
ipts-syn: use the timestamp IP option in a SYN packet when attempting to establish a TCP connection.
iprr-syn: use the record-route IP option in a SYN packet when attempting to establish a TCP connection.
ipqs-syn: use the quick-start IP option in a SYN packet when attempting to establish a TCP connection.
sack: advertise support for TCP selective acknowledgements (SACK) when establishing a TCP connection.
fo: advertise support for TCP fast open using the official IANA number assigned for fast open.
fo-exp: advertise support for TCP fast open using the testing number assigned by IANA for fast open.

-P ptbsrc

specifies the source address that should be used to send Packet Too Big messages in the pmtud test.

-q attempts

specifies the number of attempts to make with each packet to reduce false inferences caused by packet loss.

-S srcaddr

specifies the source address that should be used in TCP packets sent by the tbit test.

-T ttl

specifies the IP time-to-live value that should be used in TCP packets sent by the tbit test.

-u url

specifies a url to use when using the http application method. If the url starts with https, the tbit test begins with a TLS handshake.

-U userid

specifies an unsigned integer to include with the data collected; the meaning of the user-id is entirely up to the user and has no effect on the behaviour of tbit.

-w wscale

specifies the window scale option to use when establishing the TCP connection.

TRACELB OPTIONS

The tracelb command is used to infer all per-flow load-balanced paths between a source and destination using the multipath discovery algorithm (MDA). The following options are available for the scamper tracelb command:

tracelb [-c confidence] [-d dport] [-f firsthop] [-g gaplimit] [-O option] [-P method] [-q attempts] [-r rtraddr] [-Q maxprobec] [-s sport] [-t tos] [-U userid] [-w wait-timeout] [-W wait-probe]

-c confidence

specifies the level of confidence we want to attain that there are no more parallel load balanced paths at a given hop. Valid values are 95 (default) and 99, for 95% confidence and 99% confidence respectively.

-d dport

specifies the base destination port to use. Defaults to 33435, the default used by traceroute(8).

-f firsthop

specifies how many hops away we should start probing.

-g gaplimit

specifies how many consecutive unresponsive hops are permitted before probing down a branch halts. Defaults to three.

-O option

allows tracelb behaviour to be further tailored. The current choices for this option are:

ptr: do Domain Name System pointer (PTR) record lookups for IP addresses.

-P method

specifies which method we should use to do the probing. Valid options are: UDP-dport, ICMP-echo, UDP-sport, TCP-sport, and TCP-ack-sport. Note: scamper uses UDP-dport by default, and these options are case insensitive.

-q attempts

specifies how many probes we should send in an attempt to receive a reply. Defaults to 2.

-Q maxprobec

specifies the maximum number of probes we ever want to send. Defaults to 3000.

-r rtraddr

specifies the IP address of the router to use.

-s sport

specifies to the source port to use when sending probes. Default based on process ID.

-t tos

specifies the value for the IP Type-of-service field for outgoing probes. Defaults to 0.

-U userid

specifies an unsigned integer to include with the data collected; the meaning of the user-id is entirely up to the user and has no effect on the behaviour of tracelb.

-w wait-timeout

specifies in seconds how long to wait for a reply to a probe. Defaults to 5.

-W wait-probe

specifies in 1/100ths of seconds how long to wait between probes. Defaults to 25 (i.e. 250ms).

STING OPTIONS

The sting command is used to infer one-way loss using an algorithm with TCP probes. It requires the firewall be enabled in scamper using the -F option. The following options are available for the scamper sting command:

sting [-c count] [-d dport] [-f distribution] [-h request] [-H hole] [-i inter] [-m mean] [-s sport]

-c count: specifies the number of samples to make. By default 48 samples are sent, as this value is the current default of the FreeBSD TCP reassembly queue length. Sting 0.7 uses 100 samples.
-d dport: specifies the base destination port to use. Defaults to 80, the default port used by the HTTP protocol.
-f distribution: specifies the delay distribution of samples. By default a uniform distribution is constructed. Other distributions are currently not implemented in scamper's implementation of sting.
-h request: specifies the default request to make. Currently not implemented.
-H hole: specifies the size of the initial hole left in the request. The default is 3 bytes, the same as sting-0.7.
-i inter: specifies the inter-phase delay between data seeding and hole filling, in milliseconds. By default, sting waits 2000ms between phases.
-m mean: specifies the mean rate to send packets in the data phase, in milliseconds. By default, sting waits 100ms between probes.
-s sport: specifies to the source port to use when sending probes. Default is based on the process ID.

SNIFF OPTIONS

The sniff command is used to capture packets matching a specific signature. At present, the only supported signature is ICMP echo packets with a specific ID value, or packets containing such a quote. The following options are available for the scamper sniff command:

sting [-c limit-pktc] [-G limit-time] [-S ipaddr] [-U userid] <expression>

-c limit-pktc: specifies the maximum number of packets to capture.
-G limit-time: specifies the maximum time, in seconds, to capture packets.
-S ipaddr: specifies the IP address that packets must arrive using. scamper uses the IP address to identify the appropriate interface to listen for packets.
-U userid: specifies an unsigned integer to include with the data collected; the meaning of the user-id is entirely up to the user and has no effect on the behaviour of sniff.

The sole supported expression is icmp[icmpid] == X, where X is the ICMP-ID to select.

DATA COLLECTION FEATURES

scamper has two data output formats. The first is a human-readable format suitable for one-off data collection and measurement. The second, known as warts, is a binary format that records much more meta-data and is more precise than the human-readable format.

scamper is designed for Internet-scale measurement, where large lists of targets are supplied for probing. scamper has the ability to probe multiple lists simultaneously, with each having a mix rate that specifies the priority of the list. scamper can also make multiple cycles over a list of addresses.

When writing output to a warts file, scamper records details of the list and cycle that each measurement task belongs to.

CONTROL SOCKET

When started with the -P option, scamper allows inter-process communication via a TCP socket bound to the supplied port on the local host. This socket is useful for controlling the operation of a long-lived scamper process. A client may interact with scamper by using telnet(1) to open a connection to the supplied port.

The following control socket commands are available.

exit

The exit command closes the current control socket connection.

attach argument ...

The attach command changes how scamper accepts and replies to commands, returning results straight over the control socket. See ATTACH section below for details on which commands scamper accepts.

format string: The data format requested. The two options are warts, and json. The warts binary data is uuencoded. The json is plain json text. By default, scamper uses warts.
priority uint32_t: The mixing priority of this source, relative to other scamper sources. By default, scamper uses a priority of '1' -- all sources are mixed equally.

get argument

The get command returns the current setting for the supplied argument. Valid argument values are: holdtime, monitorname, nameserver, pid, pps, sport, version.

set argument ...

The set command sets the current setting for the supplied argument. Valid argument values are: holdtime, monitorname, nameserver, pps.

source argument ...

add arguments

The source add command allows a new input source to be added. It accepts the following arguments:

name string: The name of the source. This parameter is mandatory.
descr string: An optional string describing the source.
command string: The command to execute for each address supplied. If not supplied, the default command is used.
list_id uint32_t: An optional numeric list identifier, assigned by a human. If not supplied, a value of zero is used.
cycle_id uint32_t: An optional numeric initial cycle identifier to use, assigned by a human. If not supplied, a value of one is used.
priority uint32_t: An optional numeric value that specifies the mix rate of measurements from the source compared to other sources. If not supplied, a mix rate of one is used. A value of zero causes the source to be created, but not actively used.
outfile string: The name of the output file to write results to, previously defined with outfile open. If not supplied, the default output file is used.
file string: The name of the input file to read target addresses from. This parameter is mandatory if the source is a managed source.
cycles integer: The number of cycles to make over the target address file. If zero, scamper will loop indefinitely over the file. This parameter is ignored unless a managed source is defined.
autoreload [on | off]: This parameter specifies if the target address file should be re-read whenever a cycle is completed, or if the same set of target addresses as the previous cycle should be used. If not specified, the file is not automatically reloaded at cycle time.

update name arguments

The source update command allows some properties of an existing source to be modified. The source to update is specified with the name parameter. Valid parameters are: autoreload, cycles, and priority.

list ...

The source list command provides a listing of all currently defined sources. The optional third name parameter restricts the listing to the source specified.

cycle name

The source cycle command manually inserts a cycle marker in an adhoc source.

delete name

The source delete command deletes the named source, if possible.

outfile argument ...

The outfile commands provide the ability to manage output files. It accepts the following arguments:

open ...

The outfile open command allows a new output file to be defined. It accepts the following parameters:

name alias: The alias of the output file. This parameter is mandatory.
file string: The filename of the output file. This parameter is mandatory.
mode [truncate | append]: How the file will be opened. If the append mode is used, any existing file with the specified name will be appended to. If the truncate mode is used, any existing file will be truncated when it is opened.

close alias

The outfile close command allows an existing output file to be closed. The mandatory alias parameter specifies which output file to close. An output file that is currently referenced is not able to be closed. To close a file that is currently referenced, a new outfile must be opened, and then the outfile swap command be used.

swap alias1 alias2

The outfile swap command swaps the file associated with each output file.

list

The outfile list command outputs a list of the existing outfiles.

observe sources

This command allows for monitoring of source events. When executed, the control socket will then supply event notices whenever a source is added, updated, deleted, finished, or cycled. Each event is prefixed with a count of the number of seconds elapsed since the Unix epoch. The following examples illustrate the event monitoring capabilities:

EVENT 1169065640 source add name
      'foo' list_id 5 priority 1

EVENT 1169065641 source update
      'foo' priority 15

EVENT 1169065642 source cycle
      'bar' id 2

EVENT 1169065650 source finish
      'bar'

EVENT 1169065661 source delete
      'foo'

shutdown argument

The shutdown argument allows the scamper process to be exited cleanly. The following arguments are supported

done: The shutdown done command requests that scamper shuts down when the current tasks, as well as all remaining cycles, have completed.
flush: The shutdown flush command requests that scamper flushes all remaining tasks queued with each list, finishes all current tasks, and then shuts down.
now: The shutdown now command causes scamper to shutdown immediately. Unfinished tasks are purged.
cancel: The shutdown cancel command cancels any pending shutdown.

ATTACH MODE

In attach mode, none of the usual interactive mode commands are usable. Instead, commands may be entered directly and results will be sent back directly over the control socket. Commands are specified just as they would be with the -I flag for a command-line invocation of scamper. Replies are split into lines by single \n characters and have one of the following formats:

ERR ...: A line starting with the 3 characters "ERR" indicates an error has occurred. The rest of the line will contain an error message.
OK id-num: A line with the 2 characters "OK" indicates that scamper has accepted the command. scamper versions after 20110623 return an id number associated with the command, which allow the task to be halted by subsequently issuing a "halt" instruction.
MORE: A line with just the 4 characters "MORE" indicates that scamper has the capacity to accept more probing commands to run in parallel.
DATA length: A line starting with the 4 characters "DATA" follow by a space then a base-10 number indicates the start of result. length specifies the number of characters of the data, including newlines. The data is in binary warts format and uuencoded before transmission.

To exit attached mode the client must send a single line containing "done". To halt a command that has not yet completed, issue a "halt" instruction with the id number returned when the command was accepted as the sole parameter.

EXAMPLES

To use the default traceroute command to trace the path to 192.0.2.1:

scamper -i 192.0.2.1

To infer Path MTU changes in the network and associate them with a traceroute path:

scamper -I "trace -P udp-paris -M 192.0.2.1"

To use paris traceroute with ICMP probes, using 3 probes per hop, sending all probes, writing to a specified warts file:

scamper -O warts -o file.warts -I "trace -P icmp-paris -q 3 -Q 192.0.2.1"

To conduct a traceroute and a ping to two different addresses using the default traceroute and ping parameters, writing to a specified warts file:

scamper -O warts -o file.warts -I "trace 192.0.2.1" "ping 192.0.2.2"

To ping a series of addresses defined in filename, probing each address 10 times:

scamper -c "ping -c 10" filename

Care must be taken with shell quoting when using commands with multiple levels of quoting, such as when giving a probe description with a dealias command. The following sends UDP probes to alternating IP addresses, one second apart, and requires the IP-ID values returned to be strictly in sequence.

scamper -O warts -o ally.warts -I "dealias -O inseq -W 1000 -m ally -p '-P udp -i 192.0.2.1' -p '-P udp -i 192.0.2.4'"

Alternatively, the following accomplishes the same, but without specifying the UDP probe method twice.

scamper -O warts -o ally.warts -I "dealias -O inseq -W 1000 -m ally -p '-P udp' 192.0.2.1 192.0.2.4"

The following command scans 198.51.100.0/28 for a matching alias to 192.0.2.4, but skips 198.51.100.3.

scamper -O warts -o prefixscan.warts -I "dealias -O inseq -W 1000 -m prefixscan -p '-P udp' -x 198.51.100.3 192.0.2.4 198.51.100.0/28"

The following uses UDP probes to enumerate all per-flow load-balanced paths towards 192.0.2.6 to 99% confidence; it varies the source port with each probe.

scamper -I "tracelb -P udp-sport -c 99 192.0.2.6"

AUTHORS

scamper was written by Matthew Luckie <mjl@luckie.org.nz>. Alistair King contributed an initial implementation of Doubletree; Ben Stasiewicz contributed an initial implementation of TBIT's PMTUD test; Stephen Eichler contributed an initial implementation of TBIT's ECN test; Boris Pfahringer adapted scamper to use GNU autotools, modularised the tests, and updated this man page. Brian Hammond of Internap Network Services Corporation provided an initial implementation of scamper's json output format. Tiange Wu contributed an initial implementation of the blind in-window TBIT test, and Robert Beverly contributed BGP protocol support for TBIT.

ACKNOWLEDGEMENTS

scamper development was initially funded by the WIDE project in association with CAIDA. Boris' work was funded by the University of Waikato's Centre for Open Source Innovation.