[rbridge] Consensus Check: Point to Point links
Dinesh G Dutt
ddutt at cisco.com
Thu Oct 4 23:05:39 PDT 2007
BPDUs in the L2 world (such as STP, LLDP etc.) are typically identified
by MAC addresses, not ethertype. Some newer protocols such as CFM & OAM
are identified by ethertype and there is supposedly a move to identify
newer BPDUs using ethertype.
The frames we're talking of sending with a fixed (or reserved) address
are the data frames. BPDUs including IS-IS will use the regular MAC
Eastlake III Donald-LDE008 wrote:
> Actually, although I'm not entirely sure, I believe that BPDUs, LLDP
> PDUs, etc., all start with an Ethertype which identifies them so, in
> principle, they could be made to work on a specially equipped point to
> point link with no outer MAC addresses. However, I don't think anyone
> has proposed that TRILL should consider omitting the outer MAC addresses
> except when that suggestion appears as part of a question asking why, if
> you want to do some optimization on a point-to-point link, you don't
> want to do even more optimization.
> -----Original Message-----
> From: Anoop Ghanwani [mailto:anoop at brocade.com]
> Sent: Thursday, October 04, 2007 1:46 PM
> To: Radia Perlman; Eastlake III Donald-LDE008
> Cc: Rbridge at postel.org
> Subject: RE: [rbridge] Consensus Check: Point to Point links
>> -----Original Message-----
>> From: rbridge-bounces at postel.org
>> [mailto:rbridge-bounces at postel.org] On Behalf Of Radia Perlman
>> Sent: Thursday, October 04, 2007 8:51 AM
>> To: Eastlake III Donald-LDE008
>> Cc: Rbridge at postel.org
>> Subject: Re: [rbridge] Consensus Check: Point to Point links
>> Personally, I need a reminder of what we are trying to
>> accomplish with this before I can have any opinion.
>> a) Is omitting the outer VLAN tag to save space?
>> b) Why put in anything for destination address other than the
>> MAC address of the next hop RBridge, or put in anything into
>> the source address other than your own MAC address?
>> It won't save space. So what does it gain?
>> c) Is there any danger if an RBridge is confused about
>> whether this is a pt-to-pt link or not?
>> I can see the advantage of omitting the entire outer header
>> if it is somehow absolutely known this is a pt-to-pt link,
>> and both ends of the link understand this.
> That wouldn't work because there are other frames that will
> have to have MAC addresses, e.g. LACP, LLDP.
>> But that isn't
>> what's being proposed here. It seems to be only omitting the
>> VLAN tag, and allowing insertion of random addresses into the
>> source and destination fields in the outer header, if I'm
>> reading it correctly.
> I don't like the idea of random addresses (is it that
> a big a deal to set them correctly?), but as long as
> it's completely optional, I don't really care.
> [By the way, even though the proposal says that it
> can be random, it really can't because we have to
> say that they cannot be from the BPDU address space
> or things like LACP and LLDP will break.]
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