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

From: Dance, Brian
Subject: Re: [lwip-users] Add support for outgoing VLAN tags?
Date: Wed, 9 Nov 2011 13:37:32 +0000

On a Windows machine I have a VLAN capable Network Card.    When the (Intel) 
driver is configured for VLAN use  the windows control panel shows a network 
interface for each vlan.   Programs using sockets are unaffected.

In the lwip contect the netif structure at the equivalent level to the Windows 
netowrk interface.   I think this means that there is a possible vlan output 
implementation for lwip based on adding vlan/qos info to netif without any 
socket changes.

Below the socket level it will be necessary to locate the correct netif to use 
for output.  I would expect different vlans to be using different subnets so ip 
routing can determine which netif to use using destination ip address. 



-----Original Message-----
From: address@hidden [mailto:address@hidden On Behalf Of address@hidden
Sent: 08 November 2011 20:06
To: Mailing list for lwIP users
Subject: Re: [lwip-users] Add support for outgoing VLAN tags?

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 

> 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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