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Optical/IP

RPR Group May Swim Through 'Flooding'

The Resilient Packet Ring Technology standard might be finished, but there's more work to do. At next week's meeting in Portland, Ore., the IEEE 802.17 working group will consider some add-on technology to make RPR more attractive for Layer 2 networks.

The 802.17 standard got ratified by the IEEE late in June (see 802.17 Standard Completed). The catch is that, while the standard is complete for Layer 3 implementations, it doesn't pack the same punch when used at Layer 2.

"If you want an 802.17 ring to act as a bridge and do MAC-level forwarding, right now you lose some of the spatial reuse elegance of RPR," says John Hawkins, chair of the Resilient Packet Ring Alliance and senior marketing manager at Nortel Networks Ltd. (NYSE/Toronto: NT). Spatial reuse lets multiple traffic streams use fractions of a ring simultaneously.

This becomes a problem at Layer 2 because of "flooding," which occurs when a packet carries a MAC address that's not in a node's forwarding database. Uncertain what to do, the node broadcasts the packet everywhere it can -- all the way around the ring, in the case of RPR -- to determine which node is the destination. This doesn't come up in Layer 3 cases because each node has more complete knowledge of the surrounding world.

The problem would be solved by a technique called advanced bridging. This was originally considered for inclusion in the standard but was dropped after the 802.17 group finished compromising between two competing drafts (see RPR Moves Forward). In the end, the group saw bridging as "more of an improvement, rather than something you had to have," says Martin Green, product manager in Cisco Systems Inc.'s (Nasdaq: CSCO) Advanced Routing Technology business unit.

Corrigent Systems Inc., Luminous Networks Inc., and Nortel likewise agreed with the decision, but it still created some controversy -- at least on Light Reading's message boards. The working group will decide next week whether to tackle advanced bridging, and it's not clear whether enough interest will surface. "[Advanced bridging] will be, I think, the main issue on the table, but that issue is relevant to only some of the RPR implementations out there," says Gady Rosenfield, director of marketing at Corrigent.

Regardless of the outcome, some basic Layer 2 abilities will be added to 802.17, Hawkins says. Work is underway on what's likely to be called 802.17a, which would make RPR fit in with the basic Ethernet bridging rules of IEEE 802.1.

— Craig Matsumoto, Senior Editor, Light Reading


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Say_Yes_2_MPLS 12/5/2012 | 1:27:49 AM
re: RPR Group May Swim Through 'Flooding' According to the article: "The catch is that, while the standard is complete for Layer 3 implementations, it doesn't pack the same punch when used at Layer 2"

What?? RPR is a Layer 2 protocol, it operates at Layer 2, its nothing to do with layer 3 at all.

The article then goes on to say: "This becomes a problem at Layer 2 because of "flooding," which occurs when a packet carries a MAC address that's not in a node's forwarding database."

Flooding always takes place for unknown MAC addresses, this cannot be avoided, it is not a problem - it is how MAC bridging works. Flooding will occur when a router sends out an ARP request for an unknown IP address, this is based on an action instigated at Layer 3.

Lightreading, please can you explain exactly why you think that RPR is complete for Layer 3, and not for layer 2 - and explain exactly what layer 3 functionality is included , and exactly what layer 2 functionality is missing?
gwu3806 12/5/2012 | 1:27:39 AM
re: RPR Group May Swim Through 'Flooding' Annex F of D3.3 has specified that "remote" frames are always flooded and no spatial reuse is possible. In order to achieve spatial reuse, the traffic has to be "local", i.e., has to be sourced from and destined to RPR stations. When the RPR stations are L3 routers, the L3 routing protocols and ARP will determine the destination RPR station's MAC address. But for L2 frames transported across the RPR ring, L2 bridging does not work well, as described in Annex F.

fiberous 12/5/2012 | 1:27:18 AM
re: RPR Group May Swim Through 'Flooding' RPR has run into the 802 Union. This Union mostly
made up of raspy old men who are not fit for
any other job in most companies still think
bridging is primordial to networking.

IEEE has become a very archaic organization.
The Bridging MOB is mostly made up of Ethernet
switch vendors and their independent consultants.
802 standards have decided that within layer 2
there is a finer heirarchy - and that 802.1 is on
top while the rest of 802 is a passive and
submissive.

The day this changes and the old gas bags of dot1
wither away or just plain die of old age most of
the industry is going to languish in dealing
with bridging.

Making anything more efficient for bridging is
like making democracy more amenable to communism.





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