Jason Thorpe <thorpej@nas.nasa.gov> writes:

> On Sat, 15 May 1999 08:26:13 -0700 
>  Matt Thomas <matt@3am-software.com> wrote:
> 
>  > Out of curiousity, what protocol?
> 
> PPP Over Ethernet (RFC 2516).  pppd(8) has one socket for the IPCP/LCP/etc.
> packets anbd the PPPoE Discovery packets.  PPPoE Session and Discovery
> packets use different Ethertypes.  pppd(8) needs to be able to choose the
> correct code path for incoming packets, etc.
> 
> Basically, the application is like using Raw IP with IP_HDRINCL, except it
> happens at layer 2.
> 
> The idea here is that for ETHERTYPE_PPPOE and ETHERTYPE_PPPOEDISC,
> ether_input() will NOT m_adj() past the Ethernet header.

Basically it sounds like what you need is a general purpose raw
link layer socket.  I too could use this.

I haven't had time to sit down and figure out how to implement it
but here are the things I think it should have:

        It should handle 802.2 encoding as well as the non llc
        ethernet frames (I think I recall someone saying these
        were now a part of 802.2)  I believe things like fddi
        always use 802.2 (?)

        The user should be able to somehow bind a socket to only
        a specific type.  This is so e.g., all IP traffic doesn't
        come down your socket.  I'm not sure how to do this with
        item 1 above.  E.g. it sounds like your application would
        need to switch on the ethertype, whereas an LLC using
        application needs to switch on a different field.  (I'm
        not real sure of how 802.2 works, perhaps it would switch
        on the ethertype field and then a sub field in the llc
        header?)

I'm not sure if this is a part of the above but at least I need
it too.

        The user should have some way of joining a link layer
        multicast group if that interface type supports it.

The ISO code has a really nice raw-like link socket, except that
its type specific.  It takes as a destination sockaddr a
sockaddr_dl. Presumably this is what a raw link layer socket
would also take (if only for the if_index to determine which
interface to go out

Chris.