[rbridge] How is an IS-IS packet differentiated from layer 3 IS-IS, and TRILL-encapsulated data packets?

[Silvano Gai]

Erik,

You are correct, I oversimplified the explanation, but the conclusion
still holds

-- Silvano

> -----Original Message-----
> From: Erik Nordmark [mailto:erik.nordmark at sun.com]
> Sent: Wednesday, May 30, 2007 11:02 AM
> To: Silvano Gai
> Cc: Radia Perlman; Eastlake III Donald-LDE008; Rbridge at postel.org
> Subject: Re: [rbridge] How is an IS-IS packet differentiated from
layer 3
> IS-IS, and TRILL-encapsulated data packets?
> 
> Silvano Gai wrote:
> 
> > The advantage of using a reserved bit is that the frame with
Ethertype =
> TRILL already go through DR blocked ports. The non-TRILL IS-IS frames
will
> have Ethertype = ISIS and will be dropped by DR blocked ports.
> 
> I don't know if this matters, but AFAIK (and after checking RFC 1142),
> there is no Ethertype for IS-IS. Instead IS-IS uses a 802.3 header
(i.e.
> a length field instead of an Ethertype field) followed by 3 bytes of
LLC
> header with the SAP 0xFE. Thus the 3 bytes after the length field is
03
> FE FE.
> 
>     Erik
>