man pages section 1: User Commands

Exit Print View

Updated: July 2014

ndiff (1)


ndiff - Utility to compare the results of Nmap scans


ndiff [options] {a.xml} {b.xml}


User Commands                                            NDIFF(1)

     ndiff - Utility to compare the results of Nmap scans

     ndiff [options] {a.xml} {b.xml}

     Ndiff is a tool to aid in the comparison of Nmap scans. It
     takes two Nmap XML output files and prints the differences
     between them. The differences observed are:

     o   Host states (e.g. up to down)

     o   Port states (e.g. open to closed)

     o   Service versions (from -sV)

     o   OS matches (from -O)

     o   Script output

     Ndiff, like the standard diff utility, compares two scans at
     a time.

     -h, --help
         Show a help message and exit.

     -v, --verbose
         Include all hosts and ports in the output, not only
         those that have changed.

         Write output in human-readable text format.

         Write output in machine-readable XML format. The
         document structure is defined in the file ndiff.dtd
         included in the distribution.

     Any other arguments are taken to be the names of Nmap XML
     output files. There must be exactly two.

     Let's use Ndiff to compare the output of two Nmap scans that
     use different options. In the first, we'll do a fast scan
     (-F), which scans fewer ports for speed. In the second,
     we'll scan the larger default set of ports, and run an NSE

         # nmap -F -oX scanme-1.xml
         # nmap --script=html-title -oX scanme-2.xml

Ndiff                Last change: 11/29/2012                    1

User Commands                                            NDIFF(1)

         $ ndiff -v scanme-1.xml scanme-2.xml
         -Nmap 5.35DC1 at 2010-07-16 12:09
         +Nmap 5.35DC1 at 2010-07-16 12:13

          Host is up.
         -Not shown: 95 filtered ports
         +Not shown: 993 filtered ports
          22/tcp    open   ssh
          25/tcp    closed smtp
          53/tcp    open   domain
         +70/tcp    closed gopher
          80/tcp    open   http
         +|_ html-title: Go ahead and ScanMe!
          113/tcp   closed auth
         +31337/tcp closed Elite

     Changes are marked by a - or + at the beginning of a line.
     We can see from the output that the scan without the -F fast
     scan option found two additional ports: 70 and 31337. The
     html-title script produced some additional output for port
     80. From the port counts, we may infer that the fast scan
     scanned 100 ports (95 filtered, 3 open, and 2 closed), while
     the normal scan scanned 1000 (993 filtered, 3 open, and 4

     The -v (or --verbose) option to Ndiff made it show even the
     ports that didn't change, like 22 and 25. Without -v, they
     would not have been shown.

     There are two output modes: text and XML. Text output is the
     default, and can also be selected with the --text option.
     Text output resembles a unified diff of Nmap's normal
     terminal output. Each line is preceded by a character
     indicating whether and how it changed.  - means that the
     line was in the first scan but not in the second; + means it
     was in the second but not the first. A line that changed is
     represented by a - line followed by a + line. Lines that did
     not change are preceded by a blank space.

     Example 1 is an example of text output. Here, port 80 on the
     host gained a service version
     (lighttpd 1.5.0). The host at changed its
     reverse DNS name. The host at was completely
     absent in the first scan but came up in the second.

     Example 1. Ndiff text output

         -Nmap 4.85BETA3 at 2009-03-15 11:00
         +Nmap 4.85BETA4 at 2009-03-18 11:00

Ndiff                Last change: 11/29/2012                    2

User Commands                                            NDIFF(1)

          Host is up.
          Not shown: 99 filtered ports
         -80/tcp open  http
         +80/tcp open  http    lighttpd 1.5.0
 ( (
          Host is up.
          Not shown: 100 filtered ports

         +Host is up.
         +Not shown: 98 filtered ports
         +80/tcp  open  http     Apache httpd 1.3.41.fb1
         +443/tcp open  ssl/http Apache httpd 1.3.41.fb1

     XML output, intended to be processed by other programs, is
     selected with the --xml option. It is based on Nmap's XML
     output, with a few additional elements to indicate
     differences. The XML document is enclosed in nmapdiff and
     scandiff elements. Host differences are enclosed in hostdiff
     tags and port differences are enclosed in portdiff tags.
     Inside a hostdiff or portdiff, a and b tags show the state
     of the host or port in the first scan (a) or the second scan

     Example 2 shows the XML diff of the same scans shown above
     in Example 1. Notice how port 80 of is enclosed in portdiff tags.
     For, the old hostname is in a tags and the new
     is in b. For the new host, there is a b in the
     hostdiff without a corresponding a, indicating that there
     was no information for the host in the first scan.

     Example 2. Ndiff XML output

         <?xml version="1.0" encoding="UTF-8"?>
         <nmapdiff version="1">
                 <status state="up"/>
                 <address addr="" addrtype="ipv4"/>
                   <hostname name=""/>
                   <extraports count="99" state="filtered"/>

Ndiff                Last change: 11/29/2012                    3

User Commands                                            NDIFF(1)

                     <port portid="80" protocol="tcp">
                       <state state="open"/>
                         <service name="http"/>
                         <service name="http" product="lighttpd" version="1.5.0"/>
                 <status state="up"/>
                 <address addr="" addrtype="ipv4"/>
                     <hostname name=""/>
                     <hostname name=""/>
                   <extraports count="100" state="filtered"/>
                   <status state="up"/>
                   <address addr="" addrtype="ipv4"/>
                     <extraports count="98" state="filtered"/>
                     <port portid="80" protocol="tcp">
                       <state state="open"/>
                       <service name="http" product="Apache httpd"
                     <port portid="443" protocol="tcp">
                       <state state="open"/>
                       <service name="http" product="Apache httpd" tunnel="ssl"

Ndiff                Last change: 11/29/2012                    4

User Commands                                            NDIFF(1)


     Using Nmap, Ndiff, cron, and a shell script, it's possible
     to scan a network daily and get email reports of the state
     of the network and changes since the previous scan.
     Example 3 shows the script that ties it together.

     Example 3. Scanning a network periodically with Ndiff and

         OPTIONS="-v -T4 -F -sV"
         date=`date +%F`
         cd /root/scans
         nmap $OPTIONS $TARGETS -oA scan-$date > /dev/null
         if [ -e scan-prev.xml ]; then
                 ndiff scan-prev.xml scan-$date.xml > diff-$date
                 echo "*** NDIFF RESULTS ***"
                 cat diff-$date
         echo "*** NMAP RESULTS ***"
         cat scan-$date.nmap
         ln -sf scan-$date.xml scan-prev.xml

     If the script is saved as /root/, add the
     following line to root's crontab:

         0 12 * * * /root/

     The exit code indicates whether the scans are equal.

     o   0 means that the scans are the same in all the aspects
         Ndiff knows about.

     o   1 means that the scans differ.

     o   2 indicates a runtime error, such as the failure to open
         a file.

     Report bugs to the nmap-dev mailing list at

     Ndiff started as a project by Michael Pattrick during the
     2008 Google Summer of Code. Michael designed the program and

Ndiff                Last change: 11/29/2012                    5

User Commands                                            NDIFF(1)

     led the discussion of its output formats. He wrote versions
     of the program in Perl and C++, but the summer ended shortly
     after it was decided to rewrite the program in Python for
     the sake of Windows (and Zenmap) compatibility. This Python
     version was written by David Fifield. James Levine
     blue]released][1] a Perl script named Ndiff with similar
     functionality in 2000.

     David Fifield

     Michael Pattrick


     See attributes(5) for descriptions of the following

     |Availability   | diagnostic/nmap  |
     |Stability      | Volatile         |
      1. released

     This software was built from source available at  The original
     community source was downloaded from

     Further information about this software can be found on the
     open source community website at

Ndiff                Last change: 11/29/2012                    6