| FLOWTOP(8) | netsniff-ng toolkit | FLOWTOP(8) |
flowtop - top-like netfilter TCP/UDP/SCTP/DCCP/ICMP(v6) flow tracking
flowtop { [options] }
flowtop is a top-like connection tracking tool that can run on an end host or small home router. It is able to present TCP, UDP/UDP-lite, SCTP, DCCP, and ICMP(v6) flows that have been collected by the kernel's netfilter connection tracking framework, thus no packet capturing in user space needs to be done.
flowtop is able to give you a quick overview of current connections on your local system, e.g. for debugging purposes or to answer questions like:
* If you access website X, what other connections are being opened in
the background that I'm not aware of?
* What connections are active that pass one's router?
* I have this proprietary binary Y, to where does it connect?
* To which countries am I sending data?
* Are there any suspicious background connections on my machine?
* How many active connections does binary Y have?
* How long are connections active already?
* At which rate am I sending/receiving data?
The following information will be presented in flowtop's output:
* Application name and PID when run on local machine
* Reverse DNS for source and destination
* Geo-location information (country, city)
* Used protocols (IPv4, IPv6, TCP, UDP, SCTP, ICMP, ...)
* Flow port's service name heuristic
* Transport protocol state machine information
* Byte/packet counters (if they are enabled)
* Connection duration (if timestamping is enabled)
* Flow send/receive rate (if byte/packet counters are enabled)
In order for flowtop to work, netfilter must be active and running
on your machine, thus kernel-side connection tracking is active. If
netfilter is not running, you can activate it with iptables(8):
iptables -A INPUT -p tcp -m state --state ESTABLISHED -j ACCEPT
iptables -A OUTPUT -p tcp -m state --state NEW,ESTABLISHED -j
ACCEPT
or by loading the following kernel modules:
modprobe nf_conntrack_ipv4
modprobe nf_conntrack_ipv6
To dump byte/packet counters flowtop enables the sysctl(8)
parameter net.netfilter.nf_conntrack_acct via:
echo 1 > /proc/sys/net/netfilter/nf_conntrack_acct
and resets it to the previously set value on exit. These counters will only be
active on connections which were created after accounting was enabled. Thus,
to have these counters be active all the time the parameter should be
enabled after the system is up. To automatically enable it,
sysctl.conf(8) or sysctl.d(8) might be used.
To calculate the connection duration flowtop enables the
sysctl(8) parameter net.netfilter.nf_conntrack_timestamp via:
echo 1 > /proc/sys/net/netfilter/nf_conntrack_timestamp
and resets it to the previously set value on exit.
flowtop's intention is just to get a quick look over your active connections. If you want logging support, have a look at netfilter's conntrack(8) tools instead.
Files under /etc/netsniff-ng/ can be modified to extend flowtop's service resolution and lookup information.
* tcp.conf - TCP port/services map
* udp.conf - UDP port/services map
* geoip.conf - GeoIP database mirrors
With a fairly high rate of connection tracking updates, flowtop can become unresponsive for short periods of time while scrolling. The right fix would be to replace flowtop's connection management backend with a better design with respect to the locking approach. This is still on the "todo" list.
flowtop is licensed under the GNU GPL version 2.0.
flowtop was originally written for the netsniff-ng toolkit by Daniel Borkmann. It is currently maintained by Tobias Klauser <tklauser@distanz.ch> and Daniel Borkmann <dborkma@tik.ee.ethz.ch>.
netsniff-ng(8), trafgen(8), mausezahn(8), ifpps(8), bpfc(8), astraceroute(8), curvetun(8), iptables(8), sysctl(8), sysctl.conf(8), sysctl.d(8)
Manpage was written by Daniel Borkmann.
This page is part of the Linux netsniff-ng toolkit project. A description of the project, and information about reporting bugs, can be found at http://netsniff-ng.org/.
| 03 March 2013 | Linux |