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Pseudowire Label Switch Path Load Sharing

Pseudowire (PW) Label Switch Path (LSP) Load Sharing provides the ability for L2VPN PWs to use upto 16 or 64 Transport LSPs, depending on the platform, for carrying tunneled data across the MPLS (Multiprotocol Label Switching) network. Previously, Ethernet PWscould only use one tunnel LSP. This feature is related to traffic distribution over Link AggregationGroups (LAGs).

The current HW hashing algorithm on MPLS Transit Nodes uses MPLS labels to derive a hash value. In previous implementations where an L2VPN PW used only one Transport LSP, there were only two MPLS labels to hash on (the outer transport label, and inner VC label) for a given PW. In an eight-port LAG (Link Aggregation Group) that L2VPN tunneled traffic would only be distributed to one or two links in the LAG. When a PW uses multiple Tunnel LSPs, there are more labels for the HW to use for hashing, and this allows improved distribution over LAG in MPLS Transit Nodes

Limitations

This feature has the following limitations:

  • Support only for RSVP TE and Static LSPs (Named LSPs).
  • Named LSPs must be configured for each PW.
  • LSP-Sharing must be enabled in order to be able to configure more than one Transport LSP for a given PW.
  • Multiple PWs can use the same LSP, or set of LSPs (same as today).
  • A maximum of 16 or 64 LSPs per PW can be configured, depending on the platform.
  • If LSP-sharing is disabled when more than 1 LSP is programmed into ExtremeXOS, all LSPs used by the PW, except one, will be removed from ExtremeXOS (HAL). The configuration will not be modified.
  • A single default load sharing hashing algorithm is used. When multiple Transport LSPs are configured for a PW, the PW will be UP as long as one Transport LSP is available
  • HW counters are only supported for PW packet counts (VC LSP), not Transport LSP (outer label).
  • No support for VPWS.
  • ECMP (Equal Cost Multi Paths) is not supported in slow-path forwarding.
  • ECMP is not supported for flood traffic (unknown unicast, multicast, broadcast). These packets will only go over one LSP.
  • When multiple LSPs are configured for use by a PW, the HW counts packets for the PW only, and not individual LSPs associated with the PW. So, if there are six LSPs in use for a given PW, you will not be able to display packet counts for each individual Transport LSP.

Platforms Supported

This feature is supported on the following platforms:

  • Summit X460-G2 (16 LSPs)
  • Summit X670-G2 (16 LSPs)
  • Summit X770 (16 LSPs per PW)
  • ExtremeSwitching X870 (16 LSPs per PW)
  • ExtremeSwitching X690 (16 LSPs per PW)
Published March 2020prev | next

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