[trill] ESADI 4. Multiple attachment of the same MAC
Donald Eastlake <d3e3e3@gmail.com> Thu, 10 January 2013 22:36 UTC
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From: Donald Eastlake <d3e3e3@gmail.com>
Date: Thu, 10 Jan 2013 17:35:55 -0500
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Subject: [trill] ESADI 4. Multiple attachment of the same MAC
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Notwithstanding the claim that there were three suggested changes to ESADI below is a forth :-) Thanks, Donald ============================= Donald E. Eastlake 3rd +1-508-333-2270 (cell) 155 Beaver Street, Milford, MA 01757 USA d3e3e3@gmail.com Update RFC 6325 by updating the last sentence of the last paragraph of Section 4.2 as shown below to provide better traffic spreading while avoiding possible address flip-flopping. (The preceding two sentences are also shown for context.) Explanation: Assume some end station has two or more ports with the same MAC&VLAN that are each connected to different RBridges (RB1, RB2, ...). With ESADI, some other RBridge, RB0, can persistently see that MAC&VLAN connected to multile RBridges. When RB0 ingresses a frame for that MAC&VLAN, the current RFC 6325 text permits a wide range of behavior. In particular, it would permit RB0 to use some rule such as always send to the egress with the lowest System ID, which would put all of this traffic through one of the egress RBs and one of the end station ports. There would be no load spreading even if there were multiple different ingress RBridges and/or different MAC addresses. It also would also permit RB0 to send different traffic to different egresses by doing ECMP at a flow levee which would likely result in return traffic to RB0 from RB1, RB2, ... for the same MAC&VLAN. The resulting address flip-flopping could cause problems. The change below fixes this by requiring RB0 to use only one egress for a particular MAC&VLAN but to select that egress pseudo-randomly based on the topology including MAC reachabilty. Assuming multiple ingress RBridges and/or multiple MAC addresses, this should result in load spreading without without address flip-floping. OLD: ... However, duplicates of the same MAC within a VLAN can appear in ESADI data and between ESADI data and addresses learned from the observation of received and decapsulated frames, entered by manual configuration, or learned through Layer 2 registration protocols. If duplicate MAC addresses occur within a VLAN, RB2 sends frames to the MAC with the highest confidence. If confidences are also tied between the duplicates, for consistency it is suggested that RB2 direct all such frames (or all such frames in the same ECMP flow) toward the same egress RBridge; however, the use of other policies will not cause a network problem since transit RBridges do not examine the Inner.MacDA for known unicast frames. NEW: ... However, duplicates of the same MAC within a VLAN can appear in ESADI data and between ESADI data and addresses learned from the observation of received and decapsulated frames, entered by manual configuration, or learned through Layer 2 registration protocols. If duplicate MAC addresses occur within a VLAN, RB2 sends frames to the MAC with the highest confidence. If confidences are also tied between the duplicates then RB2 MUST, in a pseudo-random way [RFC4086], select one of the egress RBridges to which the destination MAC appears to be attached and send all traffic for the destination MAC and VLAN to that egress. Such pseudo-random selection will, over a population of ingress RBridges, probabilistically spread traffic over the possible egress RBridges. Reasonable inputs to the pseudo-random selection are the ingress RBridge System ID and/or nickname, the VLAN, the destination MAC address, and a vector of the RBridges with connectivity to that MAC and VLAN. There is no need for different RBridges to use the same pseudo-random function.
- [trill] ESADI 4. Multiple attachment of the same … Donald Eastlake