scamper - Online in the Cloud

PROGRAM:

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] [-d debugfile] [-e pidfile] [-O options]
[-i IPs | -I cmds | -f file | -P [ip:]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, as well as MDA traceroute,
alias resolution, some parts of tbit, sting, and neighbour discovery.

scamper has four modes of operation. First, scamper can be supplied a list of 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 addresses in a listfile, one address per line, using the
-f option. Third, scamper can be supplied a list of complete commands on the command line
with the -I option. Finally, 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.

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
- neighbourdisc
- ping
- trace
- tracelb
- sniff
- sting
- tbit
scamper uses trace by default. The available commands and their options are
documented below.

-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. To use
the firewall on FreeBSD and MacOS X systems, pass ipfw here.

-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 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.
- 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: do not use TLS anywhere in scamper, including tbit.

-i IP 1..N
specifies the 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 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.

-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 traceroute. 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] [-o offset] [-O option] [-p payload] [-P method] [-q attempts]
[-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.

-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.

-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.

-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.

-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. By default, UDP-
paris is used.

-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.

-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 ping. The following variations of the ping(8)
options are available:

ping [-R] [-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] [-s size]
[-S srcaddr] [-T timestamp] [-U userid] [-W timeout] [-z tos]

-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.
- 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.
- 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, udp, and
udp-dport.

-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.

-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.

-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 milliseconds 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.

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, and respond to Explicit Congestion Notification. The following options are
available for the scamper tbit command:

tbit [-t type] [-p app] [-d dport] [-s sport] [-b ASN] [-f cookie] [-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, 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.

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

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

-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 for the http application.

-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. The following options are available for the scamper tracelb command:

tracelb [-c confidence] [-d dport] [-f firsthop] [-g gaplimit] [-P method] [-q attempts]
[-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.

-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".
Defaults to "udp-dport".

-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.

-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
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 are accepted.

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

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

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