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

[address@hidden]

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).

Simon