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Reducing the Number of MAC Addresses Visible to Bridges in the Data Center

Reducing the Number of MAC Addresses Visible to Bridges in the Data Center. Bob Sultan ( bsultan@huawei.com ) Ben Mack-Crane Linda Dunbar. Problem: MAC per VNIC requires big FDB. MAC Addresses could number in hundreds of thousands. e.g., 25 access bridges per core bridge.

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Reducing the Number of MAC Addresses Visible to Bridges in the Data Center

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  1. Reducing the Number of MAC Addresses Visible to Bridges in the Data Center Bob Sultan (bsultan@huawei.com) Ben Mack-Crane Linda Dunbar

  2. Problem: MAC per VNIC requires big FDB MAC Addresses could number in hundreds of thousands e.g., 25 access bridges per core bridge e.g., 25 racks per access bridge e.g., 25 blades per rack e.g., 50 VNICs per blade • Hypervisor requires MAC address per VNIC; • MAC per VNIC implies many MAC Addresses; • Result is FDB overflow, flooding, poor performance; • Our server guys say this is the real problem in the Data Center.

  3. Proposed: MAC Address Summary AA22 AA24 AA25 AA26 SA=AA23 SA=AA00, [23] SA=AA23 SA=AA17 SA=AA00, [17] SA=AA17 SA=AA42 SA=AA00, [42] SA=AA42 summarize here restore here VNIC NIC BB39 BB40 BB41 BB42 DD77 DD78 DD79 DD80 CC25 CC26 CC27 CC28 • VNIC MAC Addresses having common high-order bits (eg., AA) are represented by a single MAC address (eg., AA00) in the network core; • FDB entries in core reduced from ‘one per VNIC’ to ‘one per NIC (or blade, or rack)’.

  4. LoTag Carries Low-order Bits needed to Restore DDDDDD000078 AAAAAA000023 data DA SA restore summarize DDDDDD000000 AAAAAA000000 DA data SA LoTag 8 bytes 16 bits 24 bits 24 bits LO Ethertype DLO SLO 000078 000023 • Tag added for Summarization; • Low-order bits (red) copied to DLO / SLO; • Low-order bits of DA / SA replaced by zeros; • Restoration reverses the procedure;

  5. When the NIC Doesn’t Support S/R AA22 AA24 AA25 AA26 Deploy S/R port on external bridge No S/R Function Here S/R BB39 BB40 BB41 BB42 DD77 DD78 DD79 DD80 CC25 CC26 CC27 CC28 • When NIC does not support Summary/Restore (S/R) function, the function can be supported on the NIC-facing port of the external bridge; • The same MAC reduction benefits are realized.

  6. Independent of the Type of Forwarding Function AA22 AA24 AA25 AA26 Port Multiplexer BB39 BB40 BB41 BB42 DD77 DD78 DD79 DD80 CC25 CC26 CC27 CC28 • It is immaterial whether the forwarding device with which the S/R function is associated is a Bridge or a Port MUX (e.g., a VEPA or IV); • The S/R function will operate in the same manner.

  7. Deploying S/R Further Up the Bridge Hierarchy AA22 AA24 AA25 AA26 No MAC reduction on this bridge Deploy S/R here or here No S/R Function here or here S/R BB39 BB40 BB41 BB42 DD77 DD78 DD79 DD80 CC25 CC26 CC27 CC28 • S/R can be deployed further up the hierarchy; • Bridges outside S/R boundary do not realize MAC reduction; • Useful when migrating to summarization.

  8. Talking with a NIC that Doesn’t Summarize AA22 AA24 AA25 AA26 S/R provisioned with info that frames to 1234 must not be summarized No S/R Function Here 1234 BB39 BB40 BB41 BB42 CC25 CC26 CC27 CC28 • AA22 not tagged when sending to 1234 which lacks S/R; • AA22 tagged when sending to CC26; • S/R at AA will allows untagged frame from 1234 to pass directly to AA25; • Maximize tagging while avoiding errors.

  9. Talking with a NIC that Doesn’t Summarize AA22 AA24 AA25 AA26 Y X 5678 1234 BB39 BB40 BB41 BB42 • When sending from 1234 to AA22, a Tag is created at Y and the DLO/SLO fields are populated as usual. It is not necessary to zero the low-order bits of the SA (as the SA is not summarized in this case; • When sending from AA22 to 1234, a Tag is created at X and the DLO/SLO fields are populated as usual. It is not necessary to zero the low-order bits of the DA (as the DA is not summarized in this case;

  10. When the SA is not Summarized 1234 AA22 data DA SA restore summarize 1234 AA00 DA data SA LoTag 8 bytes 16 bits 24 bits 24 bits LO Ethertype DLO SLO 34 22 • Tagging at X when AA22 sends to 1234 (see previous slide); • SA is summarized as usual; DA is not summarized; • MAC Reduction is realized for the SA;

  11. Key Points • Increasing numbers of VNICs per NIC creates significant scaling problem in large Data Center; • Summarization can reduce MAC awareness from ‘one MAC per VNIC’ to ‘one MAC per NIC’; • Summarization preserves the common practice of assigning one MAC address per VNIC; • Summarization can be deployed on a NIC or on an external bridge port; • Summarization can be performed on the DA and not on the SA or on the SA and not on the DA; • Summarization is independent of whether the attached device is a Bridge or a Port MUX Device.

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