ntop Man page

Resume Wikipedia de Ntop

Ntop (Network TOP) est un outil libre de supervision réseau. C’est une application qui produit des informations sur le trafic d’un réseau en temps réel (comme pourrait le faire la commande top avec les processus).
Il capture et analyse les trames d’une interface donnée, et permet d’observer une majeure partie des caractéristiques du trafic (entrant et sortant) et accepte pour cela, notamment deux modes de fonctionnement: Une interface web et un mode interactif.
Ntop est développé par Luca Deri. La version courante est la 4.1.0. C’est une application portable sur la plupart des plates-formes Unix : Linux (Debian, RedHat, Slackware, SuSe), IRIX, Solaris (i386 et SPARC), HP-UX 11.X, FreeBSD 3.X, AIX 4.1, et Windows 95/98/NT (Luca Deri a développé une libpcap pour Win32).
Il s’appuie sur la bibliothèque nommée “libpcap” pour effectuer les captures de trames (bibliothèque de capture portable du domaine public pour les systèmes Unix).

Resume Wikipedia de Ntop

Ntop (Network TOP) est un outil libre de supervision réseau. C’est une application qui produit des informations sur le trafic d’un réseau en temps réel (comme pourrait le faire la commande top avec les processus).
Il capture et analyse les trames d’une interface donnée, et permet d’observer une majeure partie des caractéristiques du trafic (entrant et sortant) et accepte pour cela, notamment deux modes de fonctionnement: Une interface web et un mode interactif.
Ntop est développé par Luca Deri. La version courante est la 4.1.0. C’est une application portable sur la plupart des plates-formes Unix : Linux (Debian, RedHat, Slackware, SuSe), IRIX, Solaris (i386 et SPARC), HP-UX 11.X, FreeBSD 3.X, AIX 4.1, et Windows 95/98/NT (Luca Deri a développé une libpcap pour Win32).
Il s’appuie sur la bibliothèque nommée “libpcap” pour effectuer les captures de trames (bibliothèque de capture portable du domaine public pour les systèmes Unix).

NTOP(8) System Manager’s Manual NTOP(8)


ntop – display top network users


ntop [@filename] [-a|–access-log-file ] [-b|–disable-decoders] [-c|–sticky-hosts] [-e|–max-table-rows] [-f|–traffic-dump-file
file>] [-g|–track-local-hosts] [-h|–help] [-l|–pcap-log ] [-m|–local-subnets ] [-n|–numeric-ip-addresses] [-p|–pro‐
tocols ] [-q|–create-suspicious-packets] [-r|–refresh-time
] [-s|–no-promiscuous] [-t|–trace-level ] [-x
] [-w|–http-server ] [-z|–disable-ses‐
sions] [-A|–set-admin-password password] [-B|–filter-expression
expression] [-C ] [-D|–domain ] [-F|–flow-spec
] [-M|–no-interface-merge] [-N|–wwn-map ] [-O|—-out‐
put-packet-path ] [-P|–db-file-path ] [-Q|–spool-file-
path ] [-U|–mapper ] [-V|–version] [-X ] [–disable-instantsessionpurge] [–disable-mutexextrainfo] [–disable-ndpi] [–disable-python] [–instance] [–p3p-cp] [–p3p-uri] [–skip-version-check=yes] [–w3c] [-4|–ipv4] [-6|–ipv6]

Unix options:

[-d|–daemon] [-i|–interface ] [-u|–user ] [-K|–enable-
debug] [-L] [–pcap_setnonblock] [–use-syslog= ] [–web‐
server-queue ]

Windows option:

[-i|–interface ]

OpenSSL options:

[-W|–https-server ] [–ssl-watchdog]


ntop shows the current network usage in a web browser, the default URL
is ‘http://localhost:3000’. It displays a list of hosts that are cur‐
rently using the network and reports information concerning the (IP and
non-IP) traffic generated and received by each host. ntop may operate
as a front-end collector (sFlow and/or netFlow plugins) or as a stand-
alone program.

ntop is a hybrid layer 2 / layer 3 network monitor, that is by default
it uses the layer 2 Media Access Control (MAC) addresses AND the layer
3 tcp/ip addresses. ntop is capable of associating the two, so that ip
and non-ip traffic (e.g. arp, rarp) are combined for a complete picture
of network activity.



The text of filename is copied – ignoring line breaks and comment
lines (anything following a #) – into the command line. ntop behaves
as if all of the text had simply been typed directly on the command
line. For example, if the command line is “-t 3 @d -u ntop” and file
d contains just the line ‘-d’, then the effective command line is -t 3
-d -u ntop. Multiple @s are permitted. Nested @s (an @ inside the
file) are not permitted.

Remember, most ntop options are “sticky”, that is they just set an
internal flag. Invoking them multiple times doesn’t change ntop’s
behavior. However, options that set a value, such as –trace-level,
will use the LAST value given: –trace-level 2 –trace-level 3 will
run as –trace-level 3.

Beginning with ntop 3.1, many command-line options may also be set via
the web browser interface. These changes take effect on the next run
of ntop and on each subsequent run until changed.

-a | –access-log-file
By default ntop does not maintain a log of HTTP requests to the inter‐
nal web server. Use this parameter to request logging and to specify
the location of the file where these HTTP requests are logged.

Each log entry is in Apache-like style. The only difference between
Apache and ntop logs is that an additional column has been added which
has the time (in milliseconds) that ntop needed to serve the request.
Log entries look like this: – – [04/Sep/2003:20:38:55 -0500] – “GET / HTTP/1.1” 200 1489 4 – – [04/Sep/2003:20:38:55 -0500] – “GET /index_top.html HTTP/1.1” 200 1854 4 – – [04/Sep/2003:20:38:55 -0500] – “GET /index_inner.html HTTP/1.1” 200 1441 7 – – [04/Sep/2003:20:38:56 -0500] – “GET /index_left.html HTTP/1.1” 200 1356 4 – – [04/Sep/2003:20:38:56 -0500] – “GET /home_.html HTTP/1.1” 200 154/617 9 – – [04/Sep/2003:20:38:56 -0500] – “GET /home.html HTTP/1.1” 200 1100/3195 10 – – [04/Sep/2003:20:38:56 -0500] – “GET /About.html HTTP/1.1” 200 2010 10

This parameter is the complete file name of the access log. In prior
releases it was erroneously called –access-log-path.

-b | –disable-decoders
This parameter disables protocol decoders.

Protocol decoders examine and collect information about layer 2 proto‐
cols such as NetBIOS or Netware SAP, as well as about specific tcp/ip
(layer 3) protocols, such as DNS, http and ftp.

This support is specifically coded for each protocol and is different
from the capability to count raw information (packets and bytes) by
protocol specified by the -p | –protocols parameter, below.

Decoding protocols is a significant consumer of resources. If the ntop
host is underpowered or monitoring a very busy network, you may wish
to disable protocol decoding via this parameter. It may also be
appropriate to use this parameter if you believe that ntop has prob‐
lems handling some protocols that occur on your network.

Even if decoding is disabled, ftp-data traffic is still decoded to
look for passive ftp port commands.

-c | –sticky-hosts
Use this parameter to prevent idle hosts from being purged from mem‐

By default idle hosts are periodically purged from memory. An idle
host is identified when no packets from or to that host have been mon‐
itored for the period of time defined by the value of
PARM_HOST_PURGE_MINIMUM_IDLE in globals-defines.h.

If you use this option, all hosts – active and idle – are retained in
memory for the duration of the ntop run.

P2P users, port scans, popular web servers and other activity will
cause ntop to record data about a large number of hosts. On an active
network, this will consume a significant – and always growing – amount
of memory. It is strongly recommended that you use a filtering
expression to limit the hosts which are stored if you use –sticky-

The idle purge is a statistical one – a random selection of the eligi‐
ble hosts will be purged during each cycle. Thus it is possible on a
busy system for an idle host to remain in the ntop tables and appear
‘active’ for some considerable time after it is truly idle.

-d | –daemon
This parameter causes ntop to become a daemon, i.e. a task which runs
in the background without connection to a specific terminal. To use
ntop other than as a casual monitoring tool, you probably will want to
use this option.

WARNING: If you are running as a daemon, the messages from ntop will
be ‘printed’ on to stdout and thus dropped. You probably don’t want
to do this. So remember to also use the -L or –use-syslog options to
save the messages into the system log.

-e | –max-table-rows
This defines the maximum number of lines that ntop will display on
each generated HTML page. If there are more lines to be displayed than
this setting permits, only part of the data will be displayed. There
will be page forward/back arrows placed at the bottom of the page for
navigation between pages.

-f | –traffic-dump-file
By default, ntop captures traffic from network interface cards (NICs)
or from netFlow/sFlow probes. However, ntop can also read data from a
file – typically a tcpdump capture or the output from one of the ntop
packet capture options.

if you specify -f, ntop will not capture any traffic from NICs during
or after the file has been read. netFlow/sFlow capture – if enabled –
would still be active.

This option is mostly used for debug purposes.

-g | –track-local-hosts
By default, ntop tracks all hosts that it sees from packets captured
on the various NICs. Use this parameter to tell ntop to capture data
only about local hosts. Local hosts are defined based on the
addresses of the NICs and those networks identified as local via the
-m | –local-subnets parameter.

This parameter is useful on large networks or those that see many
hosts, (e.g. a border router or gateway), where information about
remote hosts is not desired/required to be tracked.

-h | –help
Print help information for ntop, including usage and parameters.

-i | –interface
Specifies the network interface or interfaces to be used by ntop for
network monitoring.

If multiple interfaces are used (this feature is available only if
ntop is compiled with thread support) their names must be separated
with a comma. For instance -i “eth0,lo”.

If not specified, the default is the first Ethernet device, e.g. eth0.
The specific device that is ‘first’ is highly system dependent. Espe‐
cially on systems where the device name reflects the driver name
instead of the type of interface.

By default, traffic information obtained by all the interfaces is
merged together as if the traffic was seen by only one interface. Use
the -M parameter to keep traffic separate by interface.

If you do not want ntop to monitor any interfaces, use -i none.

Under Windows, the parameter value is either the number of the inter‐
face or its name, e.g. {6252C14C-44C9-49D9-BF59-B2DC18C7B811}. Run
ntop -h to see a list of interface name-number mappings (at the end of
the help information).

-l | –pcap-log
This parameter causes a dump file to be created of the network traffic
captured by ntop in tcpdump (pcap) format. This file is useful for
debug, and may be read back into ntop by the -f | –traffic-dump-file
parameter. The dump is made after processing any filter expression (
ntop never even sees filtered packets).

The output file will be named /..pcap (Windows: /.pcap ), where is defined by the -O | –output-
packet-path parameter and is defined by this -l | –pcap-log

-m | –local-subnets
ntop determines the ip addresses and netmasks for each active inter‐
face. Any traffic on those networks is considered local. This param‐
eter allows the user to define additional networks and subnetworks
whose traffic is also considered local in ntop reports. All other
hosts are considered remote.

Commas separate multiple network values. Both netmask and CIDR nota‐
tion may be used, even mixed together, for instance

The local subnet – as defined by the interface address(es) – is/are
always local and do not need to be specified. If you do give the same
value as a NIC’s local address, a harmless warning message is issued.

-n | –numeric-ip-addresses
By default, ntop resolves IP addresses using a combination of active
(explicit) DNS queries and passive sniffing. Sniffing of DNS
responses occurs when ntop receives a network packet containing the
response to some other user’s DNS query. ntop captures this informa‐
tion and enters it into ntop’s DNS cache, in expectation of shortly
seeing traffic addressed to that host. This way ntop significantly
reduces the number of DNS queries it makes.

This parameter causes ntop to skip DNS resolution, showing only
numeric IP addresses instead of the symbolic names. This option can
useful when the DNS is not present or quite slow.

-p | –protocols
This parameter is used to specify the TCP/UDP protocols that ntop will
monitor. The format is

A simple example is –protocols=”HTTP=http|www|https|3128,FTP=ftp|ftp-
data”, which reduces the protocols displayed on the “IP” pages to

Host Domain Data HTTP FTP Other IP
ns2.attbi.com 954 63.9 % 0 0 954 240 16.1 % 240 0 0 240 16.1 % 240 0 0
toolbarqueries.google.com 60 4.0 % 60 0 0

If the is very long you may store it in a file (for
instance protocol.list). To do so, specify the file name instead of
the on the command line. e.g. ntop -p protocol.list

If the -p parameter is omitted the following default value is used:

HTTP=http|www|https|3128 3128 is Squid, the HTTP cache

Peer-to-Peer Protocols
DirectConnect=0 Dummy port as this is a pure P2P protocol

Instant Messenger

NOTE: To resolve protocol names to port numbers, they must be speci‐
fied in the system file used to list tcp/udp protocols and ports,
which is typically /etc/services file. You will have to match the
names in that file, exactly. Missing or unspecified (non-standard)
ports must be specified by number, such as 3128 in our examples above.

If you have a file named /etc/protocols, don’t get confused by it, as
that’s the Ethernet protocol numbers, which are not what you’re look‐
ing for.

-q | –create-suspicious-packets
This parameter tells ntop to create a dump file of suspicious packets.

There are many, many, things that cause a packet to be labeled as
‘suspicious’, including:

Detected ICMP fragment
Detected Land Attack against host
Detected overlapping/tiny packet fragment
Detected traffic on a diagnostic port
Host performed ACK/FIN/NULL scan
Host rejected TCP session
HTTP/FTP/SMTP/SSH detected at wrong port
Malformed TCP/UDP/ICMP packet (packet too short)
Packet # %u too long
Received a ICMP protocol Unreachable from host
Sent ICMP Administratively Prohibited packet to host
Smurf packet detected for host
TCP connection with no data exchanged
TCP session reset without completing 3-way handshake
Two MAC addresses found for the same IP address
UDP data to a closed port
Unknown protocol (no HTTP/FTP/SMTP/SSH) detected (on port 80/21/25/22)
Unusual ICMP options

When this parameter is used, one file is created for each network
interface where suspicious packets are found. The file is in tcpdump
(pcap) format and is named /ntop-suspicious-pkts..pcap,
where is defined by the -O | –output-packet-path parameter.

-r | –refresh-time
Specifies the delay (in seconds) between automatic screen updates for
those generated HTML pages which support them. This parameter allows
you to leave your browser window open and have it always displaying
nearly real-time data from ntop.

The default is 3 seconds. Please note that if the delay is very short
(1 second for instance), ntop might not be able to process all of the
network traffic.

-s | –no-promiscuous
Use this parameter to prevent ntop from setting the interface(s) into
promiscuous mode.

An interface in promiscuous mode will accept ALL Ethernet frames,
regardless of whether they directed (addressed) to the specific net‐
work interface (NIC) or not. This is an essential part of enabling
ntop to monitor an entire network. (Without promiscuous mode, ntop
will only see traffic directed to the specific host it is running on,
plus broadcast traffic such as the arp and dhcp protocols.

Even if you use this parameter, the interface could well be in promis‐
cuous mode if another application enabled it.

ntop passes this setting on to libpcap, the packet capture library.
On many systems, a non-promiscuous open of the network interface will
fail, since the libpcap function on most systems require it to capture
raw packets ( ntop captures raw packets so that we may view and ana‐
lyze the layer 2 – MAC – information).

Thus on most systems, ntop must probably still be started as root, and
this option is largely ornamental. If it fails, you will see a
***FATALERROR*** message referring to pcap_open_live() and then an
information message, “Sorry, but on this system, even with -s, it
appears that ntop must be started as root”.

-t | –trace-level
This parameter specifies the ‘information’ level of messages that you
wish ntop to display (on stdout or to the log). The higher the trace
level number the more information that is displayed. The trace level
ranges between 0 (no trace) and 5 (full debug tracings).

The default trace value is 3.

Trace level 0 is not quite zero messages. Fatal errors and certain
startup/shutdown messages are always displayed. Trace level 1 is used
to display errors only, level 2 for both errors and warnings, and
level 3 displays error, warning and informational messages.

Trace level 4 is called ‘noisy’ and it is – generating many messages
about the internal functioning of ntop. Trace level 5 and above are
‘noisy’ plus extra logs, i.e. all possible messages, with a file:line
tag prepended to every message.

-u | –user
Specifies the user ntop should run as after it initializes.

ntop must normally be started as root so that it has sufficient privi‐
leges to open the network interfaces in promiscuous mode and to
receive raw frames. See the discussion of -s | –no-promiscuous
above, if you wish to try starting ntop as a non-root user.

Shortly after starting up, ntop becomes the user you specify here,
which normally has substantially reduced privileges, such as no login
shell. This is the userid which owns ntop’s database and output

The value specified may be either a username or a numeric user id.
The group id used will be the primary group of the user specified.

If this parameter is not specified, ntop will try to switch first to
‘nobody’ and then to ‘anonymous’ before giving up.

NOTE: This should not be root unless you really understand the secu‐
rity risks. In order to prevent this by accident, the only way to run
ntop as root is to explicitly specify -u root. Don’t do it.


ntop creates a new hash/list entry for each new host/TCP session seen.
In case of DOS (Denial Of Service) an attacker can easily exhaust all
the host available memory because ntop is creating entries for dummy
hosts. In order to avoid this you can set an upper limit in order to
limit the memory ntop can use.

-w | –http-server

-W | –https-server
ntop offers an embedded web server to present the information that has
been so painstakingly gathered. An external HTTP server is NOT
required NOR supported. The ntop web server is embedded into the
application. These parameters specify the port (and optionally the
address (i.e. interface)) of the ntop web server.

For example, if started with -w 3000 (the default port), the URL to
access ntop is http://hostname:3000/, where “hostname” is the name or
address of the system where ntop is installed. For example, if ntop is
installed on the local machine, the web interface can be accessed at
http://localhost:3000. If started with a full specification, e.g. -w, ntop listens on only that address/port combination.

If -w is set to 0 the web server will not listen for http:// connec‐

-W operates similarly, but controls the port for the https:// connec‐

Some examples:

ntop -w 3000 -W 0 (this is the default setting) HTTP requests on port
3000 and no HTTPS.

ntop -w 80 -W 443 Both HTTP and HTTPS have been enabled on their most
common ports.

ntop -w 0 -W 443 HTTP disabled, HTTPS enabled on the common port.

Certain sensitive, configuration pages of the ntop web server are pro‐
tected by a userid/password. By default, these are the user/URL
administration, filter, shutdown and reset stats are password pro‐
and are accessible initially only to user admin with a password set
during the first run of ntop.

Users can modify/add/delete users/URLs using ntop itself – see the
Admin tab.

The passwords, userids and URLs to protect with passwords are stored
in a database file. Passwords are stored in an encrypted form in the
database for further security. Best practices call for securing that
database so that only the ntop user can read it.

There is a discussion in docs/FAQ about further securing the ntop

-z | –disable-sessions
This parameter disables TCP session tracking. Use it for better per‐
formance or when you don’t really need/care to track sessions.

-A | –set-admin-password
This parameter is used to start ntop , set the admin password and
quit. It is quite useful for installers that need to automatically set
the password for the admin user.

-A and –set-admin-password (without a value) will prompt the user for
the password.

You may also use this parameter to set a specific value using –set-
admin-password=value. The = is REQUIRED and no spaces are permitted!

If you attempt to run ntop as a daemon without setting a password, a
FATAL ERROR message is generated and ntop stops.

-B | –filter-expression
Filters allows the user to restrict the traffic seen by ntop on just
about any imaginable item.

The filter expression is set at run time by this parameter, but it may
be changed during the ntop run on the Admin | Change Filter web page.

The basic format is -B filter , where the quotes are REQUIRED

The syntax of the filter expression uses the same BPF (Berkeley Packet
Filter) expressions used by other packages such as tcpdump

For instance, suppose you are interested only in the traffic gener‐
ated/received by the host jake.unipi.it. ntop can then be started
with the following filter:

ntop -B src host jake.unipi.it or dst host jake.unipi.it

or in shorthand:

ntop -B host jake.unipi.it or host jake.unipi.it

See the ‘expression’ section of the tcpdump man page – usually avail‐
able at http://www.tcpdump.org/tcpdump_man.html – for further informa‐
tion and the best quick guide to BPF filters currently available.

WARNING: If you are using complex filter expressions, especially those
with =s or meaningful spaces in them, be sure and use the long option
format, –filter-expression=”xxxx” and not -B “xxxx”.

-C |
This instruments ntop to be used in two configurations: host and net‐
work mode. In host mode (default) ntop works as usual: the IP
addresses received are those of real hosts. In host mode the IP
addresses received are those of the C-class network to which the
address belongs. Using ntop in network mode is extremely useful when
installed in a traffic exchange (e.g. in the middle of the Internet)
whereas the host mode should be used when ntop is installed on the
edge of a network (e.g. inside a company). The network mode signifi‐
cantly reduces the amount of work ntop has to perform and it has to be
used whenever ntop is used to find out how the network traffic flows
and not to pin-point specific hosts.

-D | –domain
This identifies the local domain suffix, e.g. ntop.org. It may be
necessary, if ntop is having difficulty determining it from the inter‐

-F | –flow-spec
It is used to specify network flows similar to more powerful applica‐
tions such as NeTraMet. A flow is a stream of captured packets that
match a specified rule. The format is


, where the label is used to symbolically identify the flow specified
by the expression. The expression is a bpf (Berkeley Packet Filter)
expression. If an expression is specified, then the information con‐
cerning flows can be accessed following the HTML link named ‘List Net‐

For instance define two flows with the following expression Luca‐
Hosts=’host jake.unipi.it or host pisanino.unipi.it’,GatewayRoutedP‐
kts=’gateway gateway.unipi.it’ .

All the traffic sent/received by hosts jake.unipi.it or
pisanino.unipi.it is collected by ntop and added to the LucaHosts
flow, whereas all the packet routed by the gateway gateway.unipi.it
are added to the GatewayRoutedPkts flow. If the flows list is very
long you may store in a file (for instance flows.list) and specify the
file name instead of the actual flows list (in the above example, this
would be ‘ntop -F flows.list’).

Note that the double quotations around the entire flow expression are

-K | –enable-debug
Use this parameter to simplify application debug. It does three
things: 1. Does not fork() on the “read only” html pages. 2. Displays
mutex values on the configuration (info.html) page. 3. (If available
– glibc/gcc) Activates an automated backtrace on application errors.

-L | –use-syslog=facility
Use this parameter to send log messages to the system log instead of

-L and the simple form –use-syslog use the default log facility,
defined as LOG_DAEMON in the #define symbol DEFAULT_SYSLOG_FACILITY in

The complex form, –use-syslog=facility will set the log facility to
whatever value (e.g. local3, security) you specify. The = is REQUIRED
and no spaces are allowed!

This setting applies both to ntop and to any child fork()ed for
reporting. If this parameter is not specified, any fork()ed child
will use the default value and will log it’s messages to the system
log (this occurs because the fork()ed child must give up it’s access
to the parents stdout).

Because various systems do not make the permissible names available,
we have a table at the end of globals-core.c. Look for myFacility‐

-M | –no-interface-merge
By default, ntop merges the data collected from all of the interfaces
(NICs) it is monitoring into a single set of counters.

If you have a simple network, say a small LAN with a connection to the
Internet, merging data is good as it gives you a better picture of the
whole network. For larger, more complex networks, this may not be
desirable. You may also have other reasons for wishing to monitor
each interface separately, for example DMZ vs. LAN traffic.

This option instructs ntop not to merge network interfaces together.
This means that ntop will collect statistics for each interface and
report them separately.

Only ONE interface may be reported on at a time – use the Admin |
Switch NIC option on the web server to select which interface to
report upon.

Note that activating either the netFlow and/or sFlow plugins will
force the setting of -M. Once enabled, you cannot go back.

-N | –wwn-map
This options names the file providing the map of WWN to FCID/VSAN ids.

-O | –output-packet-path
This parameter defines the base path for the ntop-suspicious-
pkts.XXX.pcap and normal packet dump files.

If this parameter is not specified, the default value is the config.h
parameter CFG_DBFILE_DIR, which is set during ./configure from the
–localstatedir= parameter. If –localstatedir is not specified, it
defaults to the –prefix value plus /var (e.g. /usr/local/var).

Be aware that this may not be what you expect when running ntop as a
daemon or Windows service. Setting an explicit and absolute path value
is STRONGLY recommended if you use this facility.

-P | –db-file-path

-Q | –spool-file-path
These parameters specify where ntop stores database files.

There are two types, ‘temporary’ – that is ones which need not be
retained from ntop run to ntop run, and ‘permanent’, which must be
retained (or recreated).

The ‘permanent’ databases are the preferences, “prefsCache.db” and the
password file, “ntop_pw.db”. These are stored in the -P | –db-file-
path specified location.

Certain plugins use the -P | –db-file-path specified location for
their database (“LsWatch.db”) or (as a default value) for files

The ‘temporary’ databases are the address queue, “addressQueue.db”,
the cached DNS resolutions, “dnsCache.db” and the MAC prefix (vendor
table), “macPrefix.db”.

If only -P | –db-file-path is specified, it is used for both types of

The directories named must allow read/write and file creation by the
ntop user. For security, nobody else should have even read access to
these files.

Note that the default value is the config.h parameter CFG_DBFILE_DIR.
This is set during ./configure from the –localstatedir= parameter.
If –localstatedir is not specified, it defaults to the –prefix value
plus /var (e.g. /usr/local/var).

This may not be what you expect when running ntop as a daemon or Win‐
dows service.

Note that on versions of ntop prior to 2.3, these parameters defaulted
to “.” (the current working directory, e.g. the value returned by the
pwd command) and caused havoc as it was different when ntop was run
from the command line, vs. run via cron, vs. run from an initializa‐
tion script.

Setting an explicit and absolute path value is STRONGLY recommended.

-U | –mapper
Specifies the URL of the mapper.pl utility.

If provided, ntop creates a clickable hyperlink on the ‘Info about
host xxxxxx’ page to this URL by appending ?host=xxxxx. Any type of
host lookup could be performed, but this is intended to lookup the
geographical location of the host.

A cgi-based mapper interface to http://www.multimap.com is part of the
ntop distribution [see www/Perl/mapper.pl]).

-V | –version
Prints ntop version information and then exits.

-W | –https-server
(See the joint documentation with the -w parameter, above)

ntop sets completed sessions as ‘timed out’ and then purge them almost
instantly, which is not the behavior you might expect from the discus‐
sions about purge timeouts. This switch makes ntop respect the time‐
outs for completed sessions. It is NOT the default because a busy web
server may have 100s or 1000s of completed sessions and this would
significantly increase the amount of memory ntop uses.

ntop stores extra information about the locks and unlocks of the pro‐
tective mutexes it uses. Since ntop uses fine-grained locking, this
information is updated frequently. On some OSes, the system calls
used to collect this information (getpid() and gettimeofday()) are
expensive. This option disables the extra information. It should
have no processing impact on ntop
– however should ntop actually deadlock, we would lose the informa‐
tion that sometimes tells us why.

ntop is started without nDPI support thus application protocols are
not recognized.

ntop is started without the Python interpreter. Beware as some ntop
reports are based on python, thus disabling it will prevent some
reports to work properly.


You can run multiple instances of ntop simultaneously by specifying
different -P values (typically through separate ntop.conf files). If
you set a value for this parameter (available only on the command
line), you (1) display the ‘instance’ name on every web page and (2)
alter the log prefix from “NTOP” to your chosen value.

If you want to make the tag more obvious, create a .instance class in
style.css, e.g.:

.instance {
color: #666666;
font-size: 18pt;

Note (UNIX): To run completely different versions of the ntop binary,
you need to compile and install into a different library (using ./con‐
figure –prefix) and then specify the LD_LIBRARY_PATH before invoking,

LD_LIBRARY_PATH=/devel/lib/ntop/:… /devel/bin/ntop …args…

If present, a file of the form _ntop_logo.gif will be used
instead of the normal ntop_logo.gif. This is tested for ONLY once, at
the beginning of the ntop run. The EXACT word(s) of the –instance
flag are used, without testing if they make a proper file name. If –
for any reason – the file is not found, an informational message is
logged and the normal logo file is used. To construct your own logo,
make it a 300×40 transparent gif.

NOTE: On the web pages, ntop uses the dladdr() function. The original
Solaris routine had a bug, replicated in FreeBSD (and possibly other
places) where it uses the ARGV[0] value – which might be erroneous –
instead of the actual file name. If the ‘running from’ value looks
bogus but the ‘libraries in’ value looks OK, go with the library.



P3P is a W3C recommendation – http://www.w3.org/TR/P3P/ – for specify‐
ing personal information a site collects and what it does with the
information. These parameters allow ntop to return P3P information.
We do not supply samples.

On some platforms, the ntop web server will hang or appear to hang (it
actually just responds incredibly slowly to the first request from a
browser session), while the rest of ntop runs just fine. This is known
to be an issue under FreeBSD 4.x.

This option sets the non-blocking option (assuming it’s available in
the version of libpcap that is installed).

While this works around the problem (by turning an interrupt driven
process into a poll), it also MAY significantly increase the CPU usage
of ntop. Although it does not actually interfere with other work,
seeing ntop use 80-90% or more of the CPU is not uncommon – don’t say
we didn’t warn you.

THIS OPTION IS OFFICIALLY UNSUPPORTED and used at your own risk. Read
the docs/FAQ write-up.

By default, ntop accesses a remote file to periodically check if the
most current version is running. This option disables that check.
Please review the privacy notice at the bottom of this page for more
information. By default, the recheck period is slightly more than 15
days. This can be adjusted via a constant in globals-defines.h. If
the result of the initial check indicates that the ntop version is a
‘new development’ version (that is newer than the latest published
development version), the recheck is disabled. This is because which
fixes and enhancements were present/absent from the code.

NOTE: At present, the recheck does not work under Windows.


Enable a watchdog for ntop webserver hangs. These usually happen when
connecting with older browsers. The user gets nothing back and other
users can’t connect. Internally, packet processing continues but there
is no way to access the data through the web server or shutdown ntop
cleanly. With the watchdog, a timeout occurs after 3 seconds, and
processing continues with a log message. Unfortunately, the user sees
nothing – it just looks like a failed connection. (also available as a
./configure option, –enable-sslwatchdog)

By default, ntop generates displayable but not great html. There are
a number of tags we do not generate because they cause problems with
older browsers which are still commonly used or are important to look
good on real-world browsers. This flag tells ntop to generate ‘BET‐
TER’ (but not perfect) w3c compliant html 4.01 output. This in no way
addresses all of the compatibility and markup issues. Over time, we
would like to make ntop more compatible, but it will never be 100%.
If you find any issues, please report them to ntop-dev.

-4 | –ipv4
Use IPv4 connections.

-6 | –ipv6
Use IPv6 connections

While ntop is running, multiple users can access the traffic informa‐
tion using their web browsers. ntop does not generate ‘fancy’ or ‘com‐
plex’ html, although it does use frames, shallowly nested tables and
makes some use of JavaScript and Cascading Style Sheets.

Beginning with release 3.1, the menus are cascading dropdowns via
JSCookMenu. With release 3.2, this extends to plugins.

We do not expect problems with any current web browser, but our ability
to test with less common ones is very limited. Testing has included
Firefox and Internet Explorer, with very limited testing on other cur‐
rent common browsers such as Opera.

In documentation and this man page, when we refer to a page such as
Admin | Switch NIC, we mean the Broad category “Admin” and the detailed
item “Switch NIC” on that Admin menu.

ntop requires a number of external tools and libraries to operate.
Certain other tools are optional, but add to the program’s capabili‐

Specifies the maximum number of web server requests for the tcp/ip
stack to retain in it’s queue awaiting delivery to the ntop web
server. Requests in excess of this queue may be dropped (allowing for
retransmission) or rejected at the tcp/ip stack level, depending upon
the OS. Whatever happens, happens at the OS level, without any infor‐
mation being delivered to ntop

Required libraries include:

libpcap from http://www.tcpdump.org/, version 0.7.2 or newer. 0.8.3 or
newer is strongly recommended.

The Windows version makes use of WinPcap (libpcap for Windows) which
may be downloaded from http://winpcap.polito.it/install/default.htm.

WARNING: The 2.x releases of WinPcap will NOT support SMP machines.

gdbm from http://www.gnu.org/software/gdbm/gdbm.html

ntop requires a POSIX threads library. As of ntop 3.2, the single-
threaded version of ntop is no longer available.

The gd 2.x library, for the creation of png files, available at

The libpng 1.2.x library, for the creation of png files, available at

ntop should support both gd 1.X and libpng 1.0.x libraries but this
has not been tested. Note that there are incompatibilities if you
compile with one version of these libraries and then run with the
other. Please read the discussion in docs/FAQ before reporting ANY
problems of this nature.

(if an https:// server is desired) openSSL from the OpenSSL project
available at http://www.openssl.org.

The rrdtool library is required by the rrd plugin. rrdtool creates
‘Round-Robin databases’ which are used to store and graph historical
data in a format that permits long duration retention without growing
larger over time. The rrdtool home page is http://peo‐

ntop includes a limited version of rrdtool 1.0.49 in the myrrd/ direc‐
tory. Users of ntop 3.2 should not need to specifically install rrd‐

The sflow Plugin is courtesy of and supported by InMon Corporation,

There are other optional libraries. See the output of ./configure for
a fuller listing.

Tool locations are current as of August 2005 – please send email to
report new locations or dead links.


top, tcpdump(8). pcap(3).

By default at startup and at periodic intervals, the ntop program will
retrieve a file containing current ntop program version information.
Retrieving this file allows this ntop instance to confirm that it is
running the most current version.

The retrieval is done using standard http:// requests, which will cre‐
ate log records on the hosting system. These log records do contain
information which identifies a specific ntop site. Accordingly, you
are being notified that this individually identifiable information is
being transmitted and recorded.

You may request – via the –skip-version-check=yes run-time option –
that this check be eliminated. If you use this option, no individually
identifiable information is transmitted or recorded, because the entire
retrieval and check is skipped.

We ask you to allow this retrieval and check, because it benefits both
you and the ntop developers. It benefits you because you will be auto‐
matically notified if the ntop program version is obsolete, becomes
unsupported or is no longer current. It benefits the developers of
ntop because it allows us to determine the number of active ntop
instances, and the operating system/versions that users are running
ntop under. This allows us to focus development resources on systems
like those our users are using ntop on.

The individually identifiable information is contained in the web
server log records which are automatically created each time the ver‐
sion file is retrieved. This is a function of the web server and not
of ntop , but we do take advantage of it. The log record shows the IP
address of the requestor (the ntop instance) and a User-Agent header
field. We place information in the User-Agent header as follows:


For example:

ntop/2.2.98 host/i686-pc-linux-gnu distro/redhat release/9 kern‐
GCC/3.2.2 config(i18n) run(i; u; P; w; t; logextra; m; instantses‐
schedyield; d; usesyslog=; t) gdbm/1.8.0 openssl/0.9.7a zlib/1.1.4
access/http interfaces(eth0,eth1)

Distro and release information is determined at compile time and con‐
sists of information typically found in the /etc/release (or similar)
file. See the ntop tool linuxrelease for how this is determined.

gcc compiler version (if available) is the internal version #s for the
gcc compiler, e.g. 3.2.3.

kernrlse is the Linux Kernel version or the xBSD ‘release’ such as
4.9-RELEASE and is determined from the uname data (if it’s available).

The ./configure parameters are stripped of directory paths, leading -s,
etc. to create a short form that shows us what ./configure parameters
people are using.

Similarly, the run time parameters are stripped of data and paths, just
showing which flags are being used.

The libpcap, gdbm, openssl and zlib versions come from the strings
returned by the various inquiry functions (if they’re available).

Here’s a sample log record:

67.xxx.xxx.xxx – – [28/Dec/2003:12:11:46 -0500] “GET /version.xml
200 1568 www.burtonstrauss.com “-” “ntop/2.2.98 host/i686-pc-linux-
distro/redhat release/9 kernrlse/2.4.20-8smp GCC/3.2.2 config(i18n)
run(i; u; P; w; t; logextra; m; instantsessionpurge; schedyield; d;
usesyslog=) libpcap/0.8 gdbm/1.8.0 openssl/0.9.7a zlib/1.1.4
interfaces(eth0,eth1,eth2)” “-”

Please send bug reports to the ntop-dev mailing
list. The ntop mailing list is used for discussing ntop
usage issues. In order to post messages on the lists a (free) subscrip‐
tion is required to limit/avoid spam. Please do NOT contact the author
directly unless this is a personal question.

Commercial support is available upon request. Please see the ntop site
for further info.

Please send code patches to .


ntop’s author is Luca Deri (http://luca.ntop.org/) who can be reached
at .

ntop is distributed under the GNU GPL licence (http://www.gnu.org/).

The author acknowledges the Centro Serra of the University of Pisa,
Italy (http://www-serra.unipi.it/) for hosting the ntop sites (both web
and mailing lists), and Burton Strauss for his
help and user assistance. Many thanks to Stefano Suin and Rocco Carbone for contributing to
the project.

August 2005 (ntop 3.2) NTOP(8)