[rbridge] ARP/ND (was RE: Two "shared VLAN" alternative proposals)

[J. R. Rivers]

Why does ARP/ND equate to IP multicast optimization?

JR
 

> -----Original Message-----
> From: Eric Gray (LO/EUS) [mailto:eric.gray at ericsson.com] 
> Sent: Wednesday, April 04, 2007 7:34 AM
> To: J. R. Rivers; Silvano Gai; Caitlin Bestler; Radia 
> Perlman; rbridge at postel.org
> Subject: RE: ARP/ND (was RE: [rbridge] Two "shared VLAN" 
> alternative proposals)
> 
> JR,
> 
> 	I agree.  However, I believe we (as a working group) have
> already
> agreed that the IP multicast optimization is essential.  
> Also, it is my
> point (and it is certainly arguable) that perhaps TRILL should not be
> targetting the general applications of L2 where other forms 
> of L2 bcast
> are likely to be a significant factor - but should instead 
> focus on the
> applications of L2 specific to IP only (or IP dominant) networks.
> 
> --
> Eric Gray
> Principal Engineer
> Ericsson  
> 
> > -----Original Message-----
> > From: J. R. Rivers [mailto:jrrivers at nuovasystems.com] 
> > Sent: Wednesday, April 04, 2007 9:58 AM
> > To: Eric Gray (LO/EUS); Silvano Gai; Caitlin Bestler; Radia 
> > Perlman; rbridge at postel.org
> > Subject: RE: ARP/ND (was RE: [rbridge] Two "shared VLAN" 
> > alternative proposals)
> > Importance: High
> > 
> > 
> > It seems that if ARP is the bulk of your 
> broadcast/multicast, then you
> > don't really need a very efficient broadcast/multicast 
> > mechanism.  Some
> > networks can be characterized as you've stated; however, there are
> > others that use L2/IP multicast in a substantial fashion.
> > 
> > JR
> > 
> > 
> > > -----Original Message-----
> > > From: Eric Gray (LO/EUS) [mailto:eric.gray at ericsson.com] 
> > > Sent: Wednesday, April 04, 2007 6:14 AM
> > > To: Silvano Gai; Caitlin Bestler; J. R. Rivers; Radia 
> > > Perlman; rbridge at postel.org
> > > Subject: RE: ARP/ND (was RE: [rbridge] Two "shared VLAN" 
> > > alternative proposals)
> > > 
> > > Silvano,
> > > 
> > > 	Where IP (v4 or v6) is the exclusive higher layer in a specific
> > > network deployment, it is likely that ARP is one of the 
> most common 
> > > forms of broadcast traffic that may occur.  As we've 
> > > previously agreed 
> > > that broadcast traffic is of particular concern in TRILL, the 
> > > potential
> > > to drastically reduce (or possibly eliminate) common 
> > broadcast traffic
> > > should be considered a worth-while objective.
> > > 
> > > --
> > > Eric Gray
> > > Principal Engineer
> > > Ericsson  
> > > 
> > > > -----Original Message-----
> > > > From: Silvano Gai [mailto:sgai at nuovasystems.com] 
> > > > Sent: Tuesday, April 03, 2007 7:22 PM
> > > > To: Caitlin Bestler; J. R. Rivers; Eric Gray (LO/EUS); Radia 
> > > > Perlman; rbridge at postel.org
> > > > Subject: ARP/ND (was RE: [rbridge] Two "shared VLAN" 
> > > > alternative proposals)
> > > > Importance: High
> > > > 
> > > > 
> > > > Do we have any quantitatively data about the need of 
> ARP/ND proxy?
> > > > 
> > > > 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.
> > > > 
> > > > The ARP/ND cache on the RBridge must be significantly 
> > > shorter than 30
> > > > minutes to not increase the amount of obsolete information.
> > > > 
> > > > Are we reducing from 5 ARP/sec to 3 ARP/sec for 100 K hosts 
> > > per VLAN?
> > > > 
> > > > Is this the big optimization for which we care to create 
> > > corner cases
> > > > and potential incompatibilities?
> > > > 
> > > > -- Silvano
> > > > 
> > > > > -----Original Message-----
> > > > > From: Caitlin Bestler [mailto:caitlinb at broadcom.com]
> > > > > Sent: Tuesday, April 03, 2007 3:38 PM
> > > > > To: J. R. Rivers; Silvano Gai; Eric Gray (LO/EUS); 
> > Radia Perlman;
> > > > > rbridge at postel.org
> > > > > Subject: RE: [rbridge] Two "shared VLAN" alternative proposals
> > > > > 
> > > > > 
> > > > > 
> > > > > > -----Original Message-----
> > > > > > From: J. R. Rivers [mailto:jrrivers at nuovasystems.com]
> > > > > > Sent: Tuesday, April 03, 2007 3:31 PM
> > > > > > To: Caitlin Bestler; Silvano Gai; Eric Gray (LO/EUS); Radia
> > > > > > Perlman; rbridge at postel.org
> > > > > > Subject: RE: [rbridge] Two "shared VLAN" 
> alternative proposals
> > > > > >
> > > > > >
> > > > > > snip...
> > > > > > >
> > > > > > >
> > > > > > > At the minimum we need to ensure that all 
> RBridges have the
> > > > > > > information that would enable them to efficiently and
> > > > > > reliably act as
> > > > > > > an ARP/ND proxy.
> > > > > >
> > > > > > It depends on how you define the requirements of ARP/ND
> > > > > > proxy.  I have seen this general mechanism used in many
> > > > > > contexts... only one of which is covered by an IETF RFC
> > > > > > (AFAIK).  Bridges in their basic definition don't 
> have ARP/ND
> > > > > > proxy.  Only bridges that subsume some type of IP related
> > > > > > functionality contain these.
> > > > > >
> > > > > > If an RBridge "looks and smells" like a bridge, 
> then there is
> > > > > > natural traffic separation between VLANs, and this allows
> > > > > > systems companies to view RBridges as "better bridges".
> > > > > >
> > > > > > JR
> > > > > >
> > > > > >
> > > > > 
> > > > > The reason RBridges are "better bridges" is that they
> > > > > deal with the issues of large subnets far better than
> > > > > bridges do.
> > > > > 
> > > > > Efficient distribution of ARP/ND information is also
> > > > > an issue where a "better bridge" is needed to scale
> > > > > to larger subnets efficiently.
> > > > 
> > > > 
> > > 
> > 
>