zmap - Man Page

The Fast Internet Scanner


zmap [ -p <port> ] [ -o <outfile> ] [ Options... ] [ ip/hostname/range ]


ZMap is a network tool for scanning the entire IPv4 address space (or large samples). ZMap is capable of scanning the entire Internet in around 45 minutes on a gigabit network connection, reaching ~98% theoretical line speed.


Basic Options


IP addresses or DNS hostnames to scan. Accepts IP ranges in CIDR block notation. Defaults to 0.0.0/8

-p, --target-port=port

TCP or UDP port number to scan (for SYN scans and basic UDP scans)

-o, --output-file=name

When using an output module that uses a file, write results to this file. Use - for stdout.

-b, --blocklist-file=path

File of subnets to exclude, in CIDR notation, one-per line. It is recommended you use this to exclude RFC 1918 addresses, multicast, IANA reserved space, and other IANA special-purpose addresses. An example blocklist file blocklist.conf for this purpose.

-w, --allowlist-file=path

File of subnets to scan, in CIDR notation, one-per line. Specifying a allowlist file is equivalent to specifying to ranges directly on the command line interface, but allows specifying a large number of subnets. Note: if you are specifying a large number of individual IP addresses (more than 10 million), you should instead use --list-of-ips-file.

-I, --list-of-ips-file=path

File of individual IP addresses to scan, one-per line. This feature allows you to scan a large number of unrelated addresses. If you have a small number of IPs, it is faster to specify these on the command line or by using --allowlist-file. This should only be used when scanning more than 10 million addresses. When used in with --allowlist-path, only hosts in the intersection of both sets will be scanned. Hosts specified here, but included in the blocklist will be excluded.

Scan Options

-r, --rate=pps

Set the send rate in packets/sec. Note: when combined with --probes, this is total packets per second, not IPs per second.

-B, --bandwidth=bps

Set the send rate in bits/second (supports suffixes G, M, and K (e.g. -B 10M for 10 mbps). This overrides the --rate flag.

-n, --max-targets=n

Cap the number of targets to probe. This can either be a number (e.g. -n 1000) or a percentage (e.g. -n 0.1%) of the scannable address space (after excluding blocklist)

-N, --max-results=n

Exit after receiving this many results

-t, --max-runtime=secs

Cap the length of time for sending packets

-c, --cooldown-time=secs

How long to continue receiving after sending has completed (default=8)

-e, --seed=n

Seed used to select address permutation. Use this if you want to scan addresses in the same order for multiple ZMap runs.


Split the scan up into N shards/partitions among different instances of zmap (default=1). When sharding, --seed is required.


Set which shard to scan (default=0). Shards are 0-indexed in the range [0, N), where N is the total number of shards. When sharding --seed is required.

-P, --probes=n

Number of probes to send to each IP (default=1)


Number of times to try resending a packet if the sendto call fails (default=10)

Network Options

-s, --source-port=port|range

Source port(s) to send packets from

-S, --source-ip=ip|range

Source address(es) to send packets from. Either single IP or range (e.g.

-G, --gateway-mac=addr

Gateway MAC address to send packets to (in case auto-detection fails)


Source MAC address to send packets from (in case auto-detection fails)

-i, --interface=name

Network interface to use

-X,  --iplayer

Send IP layer packets instead of ethernet packets (for non-Ethernet interface)

Probe Options

ZMap allows users to specify and write their own probe modules. Probe modules are responsible for generating probe packets to send, and processing responses from hosts.


List available probe modules (e.g. tcp_synscan)

-M, --probe-module=name

Select probe module (default=tcp_synscan)


Arguments to pass to probe module


List the fields the selected probe module can send to the output module

Output Options

ZMap allows users to specify and write their own output modules for use with ZMap. Output modules are responsible for processing the fieldsets returned by the probe module, and outputting them to the user. Users can specify output fields, and write filters over the output fields.


List available output modules (e.g. csv)

-O, --output-module=name

Select output module (default=csv)


Arguments to pass to output module

-f, --output-fields=fields

Comma-separated list of fields to output


Specify an output filter over the fields defined by the probe module. See the output filter section for more details.

Logging and Metadata Options

-q,  --quiet

Do not print status updates once per second

-v, --verbosity=n

Level of log detail (0-5, default=3)

-l, --log-file=filename

Output file for log messages. By default, stderr.

-m, --metadata-file=filename

Output file for scan metadata (JSON)

-L,  --log-directory

Write log entries to a timestamped file in this directory

-u,  --status-updates-file

Write scan progress updates to CSV file"


Disables logging messages to syslog


Inject user-specified notes into scan metadata


Inject user-specified JSON metadata into scan metadata

Additional Options

-T, --sender-threads=n

Threads used to send packets. ZMap will attempt to detect the optimal number of send threads based on the number of processor cores.

-C, --config=filename

Read a configuration file, which can specify any other options.

-d,  --dryrun

Print out each packet to stdout instead of sending it (useful for debugging)


Maximum NIC sendto failures before scan is aborted


Minimum hitrate that scan can hit before scan is aborted


Comma-separated list of cores to pin to


Ignore invalid, malformed, or unresolvable entries in allowlist/blocklist file. Replaces the pre-v3.x --ignore-invalid-hosts option.

-h,  --help

Print help and exit

-V,  --version

Print version and exit

Output Filters

Results generated by a probe module can be filtered before being passed to the output module. Filters are defined over the output fields of a probe module. Filters are written in a simple filtering language, similar to SQL, and are passed to ZMap using the --output-filter option. Output filters are commonly used to filter out duplicate results, or to only pass only successful responses to the output module.

Filter expressions are of the form <fieldname> <operation> <value>. The type of <value> must be either a string or unsigned integer literal, and match the type of <fieldname>. The valid operations for integer comparisons are = !=, ,, =,=. The operations for string comparisons are =, !=. The --list-output-fields flag will print what fields and types are available for the selected probe module, and then exit.

Compound filter expressions may be constructed by combining filter expressions using parenthesis to specify order of operations, the && (logical AND) and || (logical OR) operators.

For example, a filter for only successful, non-duplicate responses would be written as: --output-filter="success = 1 && repeat = 0"

UDP Probe Module Options

These arguments are all passed using the --probe-args=args option. Only one argument may be passed at a time.


Path to payload file to send to each host over UDP.


Path to template file. For each destination host, the template file is populated, set as the UDP payload, and sent.


ASCII text to send to each destination host


Hex-encoded binary to send to each destination host


Print information about the allowed template fields and exit.

Mid-Scan Changes

You can change the rate at which ZMap is scanning mid-scan by sending SIGUSR1 (increase) and SIGUSR2 (decrease) signals to ZMap. These will result in the scan rate increasing or decreasing by 5%.


June 2017 ZMap