Subject: [rbridge] TTL only - was RE: New fields in shim header?

From: sgai at nuovasystems.com (Silvano Gai)
Date: Wed, 18 Oct 2006 11:04:00 -0700

> -----Original Message-----
> From: rbridge-bounces at postel.org [mailto:rbridge-bounces at postel.org]
On
> Behalf Of Erik Nordmark
> Sent: Wednesday, October 18, 2006 10:22 AM
> To: Ed Bowen
> Cc: rbridge at postel.org; rbridge-bounces at postel.org; Radia Perlman; Joe
> Touch
> Subject: Re: [rbridge] TTL only - was RE: New fields in shim header?
> 
> Ed Bowen wrote:
> 
> > What is the operational experience that indicates the requirement
for
> the
> > other environments?  I am not aware of anyone who plans to install
TRILL
> > outside of the environment Silvano outlines. What need would
motivate
> these
> > additional environments?
> 
> Here is one data point, which isn't central to TRILL but illustrate
the
> possibilities.
> 
> Barnard Aboba made the observation a long time ago that using TRILL in
> wireless access points would solve certain existing issues.
> 
> By advertising the MAC address in the link-state routing protocol when
> the station has associated, then moving from one AP to another is less
> disruptive. Today one has to rely on the station transmitting packets
> via the new AP in order for the learning bridges to find update the
> learning tables.
> 

But if the station does not send packet, how are you going to learn that
it is there and therefore propagate its existence in ISIS?

If the AP learns by other way that the station is there, it just needs
to send a dummy broadcast packet with the SA of the station to have the
learning happen. This is what is done in commercial products, for
example, when the root port dies to quickly switch to the alternate
port.

IMHO the true value of TRILL is the capability to effectively
implementing fat tree networks, which is particularly crucial in this
moment, since the speed of the access links and the speed of the
backbone links are becoming the same, i.e. 10 GE. If 100GE was available
today for the backbone, TRILL will be still important, but less
compelling. That is also the reason we need to be very careful to be HW
friendly, since TRILL will be important where ASIC design is really at
the edge of what the technology can do.

-- Silvano