[rbridge] Back to ND/ARP optimization

[Silvano Gai]

Donald,

To provide a precise answer we need to consider which of the three
schemes described in section 3.12 of 
http://www.ietf.org/internet-drafts/draft-ietf-trill-rbridge-protocol-03
.txt
the RBridge will implement.

The draft refers generically to "Some mix of these strategies".

Lacking this information, let's assume the strategy you mention.
The flood cannot be done in HW. In fact it is mandatory to not resend
the ARP on the port it was received to avoid frame duplication.

The flood must be implemented in SW has n-1 port transmissions; where n
is the number of ports.

Therefore, the CPU of a 256 port RBridge:
- in absence of ARP/ND proxy receives 1 ARP (and the HW does the correct
replication)
- with ARP/ND proxy it receives 1 ARP (and the HW does nothing)and sends
out 255 ARP messages. Huge overhead

-- Silvano


> -----Original Message-----
> From: Eastlake III Donald-LDE008 [mailto:Donald.Eastlake at motorola.com]
> Sent: Sunday, May 06, 2007 2:30 PM
> To: Silvano Gai
> Cc: rbridge at postel.org
> Subject: RE: [rbridge] Back to ND/ARP optimization
> 
> Silvano,
> 
> I don't understand what these Rbridge CPUs will be doing. If an
Rbridge
> receives a native ARP broadcast frame for an unknown IP address it
would
> just learn the source IP->MAC mapping and then flood the ARP
broadcast.
> 
> Donald
> 
> -----Original Message-----
> From: rbridge-bounces at postel.org [mailto:rbridge-bounces at postel.org]
On
> Behalf Of Silvano Gai
> Sent: Friday, May 04, 2007 3:01 PM
> To: Arien Vijn
> Cc: rbridge at postel.org; Radia.Perlman at sun.com
> Subject: Re: [rbridge] Back to ND/ARP optimization
> 
> Arien
> 
> Thanks for the real world data, which proves that ARP/ND proxy must
not
> be implemented on RBridges.
> 
> In fact, since the queries toward unused addresses are dominant, the
> ARP/ND cache will almost always miss and the RBridge CPU will be busy
> trying to remotely resolve queries that will never complete.
> 
> -- Silvano
> 
> > -----Original Message-----
> > From: Arien Vijn [mailto:arien.vijn at ams-ix.net]
> > Sent: Friday, May 04, 2007 10:04 AM
> > To: Silvano Gai
> > Cc: Arien Vijn; Radia.Perlman at sun.com; rbridge at postel.org
> > Subject: Re: [rbridge] Back to ND/ARP optimization
> >
> > Hi,
> >
> > On May 3, 2007, at 10:55 PM, Silvano Gai wrote:
> >
> > [...]
> >
> > >> Does anyone have a handle on how much traffic is caused by
ARP/ND?
> > >>
> > >
> > > With an ARP cache of 30 minutes, typical in hosts today, even with
> > > a 100
> > > K hosts in a VLAN we get at most 55 ARP seconds. Since not all the
> > > hosts
> > > talk with each other, it is more typically like 5 ARP/sec.
> > >
> > > BASICALLY NOTHING.
> >
> > Well... that might be the case if all your hosts are actually
> > answering. But query rates are pretty much determined by queries for
> > unused addresses. In other words by the query rates hosts (routers)
> > can achieve for addresses that are not in their caches.
> >
> > For what its worth. I am involved in a real network with 400+ BGP
> > routers in one broadcast domain (/23 IPv4 subnet). The average rate
> > is little over 13 queries/second. That is with ARP mitigation and
> > peak rates are much higher.
> >
> > -- Arien
> 
> 
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