Re: Question about sample

From: neil mckee <>
Date: 03/01/05
Message-Id: <>

Hello Bao,

In some switch/router architectures it is not possible to obtain the
raw packet headers efficiently, and only a subset of the protocols
fields are available. In that case the structures for IPV4, IPV6 and
ETHERNET can be used instead. However, where there is a choice it is
better to export the raw header.

The specification document at
includes the following paragraph:

    A flow_sample must contain packet header information. The
    prefered format for reporting packet header information is
    the sampled_header. However, if the packet header is not
    available to the sampling process then one or more of
    sampled_ethernet, sampled_ipv4, sampled_ipv6 may be used.

As far as I know, the only implementation that uses these structures at
the moment is our own probe software - we use it when converting Cisco
NetFlow or Riverstone LFAP to sFlow. I hope someone else will jump in
and correct me if they know of another implementation, but in any
case, I recommend that you design your receiver to accept these
structures in case they appear in the future.


On Mar 1, 2005, at 8:21 AM, Bao wrote:

> Hello everyone
> I'm just trying to make a program to analyze our network's
> traffic using sFlow. I read that the packet_data_type could get 3
> different values : HEADER (1), IPV4 (2), IPV6(3). Could anyone explain
> me in which cases we could have IPV4 ?
> I'm doing different tests on our network and the packet_data value is
> always 1 (HEADER).
> here is the flow sample structure :
> struct flow_sample {
> unsigned int sequence_number;
> unsigned int source_id;
> [...]
> packet_data_type packet_data;
> }
> Regards
> --
> Bao
> OVANET S.A.R.L -*-

Neil McKee
InMon Corp.
Received on Tue Mar 1 10:07:15 2005

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