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Re: [lwip-users] Add support for outgoing VLAN tags?

From: web
Subject: Re: [lwip-users] Add support for outgoing VLAN tags?
Date: Mon, 07 Nov 2011 09:05:22 +0100

On 5 nov 2011 15:51 "Kieran Mansley" <address@hidden> wrote:
On 2 Nov 2011, at 09:58, address@hidden wrote:
With this method it could be possible to add support for outgoing VLAN taggning for QoS purposes, without having to add a new argument to a lot of internal LwIP functions.

This sounds better than the first proposal. I am a bit worried though that it would be a feature that would be rarely used or tested. Is this something you need?

Yes, it is. It is a mandatory feature for certain protocols, such as the industrial control protocol "EtherNet/IP" http://en.wikipedia.org/wiki/Ethernet/IP
Other applications such as IP phones and IPTV can also use VLAN PCP for QoS. (But that is not where we do business)

We already have this implemented and running according to my original proposal. I am just looking for ways to reduce the number of differences between our LwIP setup and vanilla LwIP to make upgrades easier.

We talked internally a bit more about the possibility of translating the TOS field to the VLAN PCP field, and found a problem with that approach: The TOS and VLAN PCP fields must be individually configurable in "EtherNet/IP".

The problem with adding VLAN PCP to LwIP is that a socket level variable must somehow be communicated down to the link layer for each frame. There does not seem to be a easy way of doing this.

Timmy Brolin

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