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

From: address@hidden
Subject: Re: [lwip-users] Add support for outgoing VLAN tags?
Date: Tue, 08 Nov 2011 21:05:58 +0100
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:8.0) Gecko/20111105 Thunderbird/8.0

address@hidden wrote:
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

That's interesting. Since I know of at least one Ethernet/IP stack being ported to linux, do you know whether/how linux allows changing the VLAN header per socket?

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.
Thinkig about it, we already have a mechanism for that: the per-pcb ARP entry cache. In the same manner as this, we could add members to struct netif which configure VLAN settings and change them before calling one of the ip_output functions (although that set/reset code would be scattered around tcp, udp, raw, icmp and igmp).


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