[ipxe-devel] Adding lldp-agent to ipxe

Michael Brown mbrown at fensystems.co.uk
Wed Sep 25 14:45:56 UTC 2013

On 12/09/13 11:05, Thomas Mieslinger wrote:
> [...]
> It would be helpful for that overview page if I could display the
> switchport right away.
> So for me, I'd just need PortID and PortDescr. But for other uses, I
> guess that ChassisID, SysName and SysDescr could be useful.
> For naming ipxe variables, I'd propose the trick to compose the name of
> a prefix and the original variable name. Example: lldp-PortDescr which
> then would be used as ${net0/lldp-PortID:uristring}.
> Ok, so the next step would be wait for the approval of the variable
> names and then to propose a patch.

 From a quick look at the LLDP specs, it seems as though the mapping


might be reasonably natural, where <type> is the LLDP TLV type, and 
<offset> and <length> describe the offset and length of the desired data 
within the TLV value.  (As a special case, a <length> of zero could 
indicate "all remaining data".)

This would allow for some fairly simple encodings of simple values, e.g.

   ${net0.lldp/4:string} for the Port Description
   ${net0.lldp/5:string} for the System Name
   ${net0.lldp/3:uint16} for the Time To Live

while also allowing for access to the more complex LLDP data structures

   ${net0.lldp/1.0.1:uint8} for the Chassis ID Subtype
   ${net0.lldp/1.1:hex} for the Chassis ID

There seems to be no way to solicit LLDP information; iPXE would just 
have to wait for an LLDP packet to arrive.  This wait could be 
implemented within an iPXE script, e.g.:

   isset ${net0.lldp/1} && goto lldp_done
   sleep 1
   goto lldp

I'm assuming that we need to support only point-to-point LANs, and that 
we can get away with receive-only operation (i.e. no need to transmit 
our own LLDP information).


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