EHNT 0.4 review

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EHNT is a tool which turns streams of Netflow (version 5) data into something useful and human-readable

License: GPL (GNU General Public License)
File size: 0K
Developer: Nik Weidenbacher
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EHNT is a tool which turns streams of Netflow (version 5) data into something useful and human-readable. (Netflow is a UDP-based traffic reporting protocol created by Cisco, generated by Cisco, Juniper, Foundry, and other routers.)

Netflow operates in many ways. It will dump flow records in human-readable form. It will also provide reports on top ASes, IP protocols, and tcp/udp ports. The reports can be generated over various intervals, from 1 minute to 1 day.

Component programs are:

1. 'ehntserv' listens to netflow version 5 UDP packets, and also listens for client TCP connections. When a TCP client connects, the server starts forwarding all the netflow packets it receives (plus the IP address of the originating device) to that client.

ehntserv does not currently do any IP access control. I suggest that you use ipchains or iptables on your linux box, or IP Filter (ipf) ( on your Solaris or BSD box. I don't know what the current state of packet filtering is on other Unixes; IP Filter seems to support several.

2. 'ehnt' connects to ehntserv and displays the flows it receives in various ways. It currently has four modes (-m ):

- top mode displays average utilization by top ASes, IP protocols, or tcp/udp ports over a given interval (from 1 minute to 1 day).

Top mode is different when it focuses on a single interface on a single router, because then you get to see summaries of source and destionation for both inbound and outbound traffic. Otherwise, you just get summaries of source and destination.
- dump mode displays individual flows
- shortdump mode display individual flows in a more compact but hard
to read fashion
- colondump mode display individual flows in a machine-readable format.
And yes, I recognize that the name of this mode is unpleasant.

In all three modes, simple (REALLY simple) filtering can be done for AS
number, TCP/UDP port, IP protocol number, device sending the flow record,
and SNMP interface index.

You may think of ehnt in the three dump modes as a brain-dead and incredibly
simple tcpdump for netflow.

ehnt also has the silly and uninspiredly-named 'big' filter, in which it
only displays flows with are bigger (in packets or bytes) than any flow
received before it. This only makes sense in the three dump modes.

What's New in This Release:
Added Unix domain support for client connections, enabled by default

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