Subject: Re: purpose of mbuf type MT_HEADER
To: Pavel Cahyna <>
From: =?iso-8859-1?q?J=F6rn_Seger?= <>
List: tech-net
Date: 10/01/2004 11:57:28
Hi Pavel,

Am Freitag, 1. Oktober 2004 11:38 schrieb Pavel Cahyna:
> Hello,
> what is the purpose of mbuf type MT_HEADER? How is it different from
> MT_DATA? The manual page says only "data is a packet header", which is not
> clear - aren't headers of upper-layer protocols just data for lower-layer
> ones?

There are different aproached for TCP and UDP.
Stevens TCP/IP Illustrated Volume 2:
The first mbuf with the packet header for the UDP datagram has a type of=20
MT_DATA, but the first mbuf with the packet header for the TCP segment has =
type of MT_HEADER. This [..] makes no difference. Mbufs of these two types=
are essentially the same.

But I'm not completely familiar with the implementation details on NetBSD, =
someone might correct me if this is not true any more.