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18. Frame Ordering

18. Frame Ordering​

In a MAC address, if the value of the first nibble (bits 8 through 5) of the most significant octet of the destination MAC address (which follows the last MPLS label) happens to be 0x4 or 0x6, then the Ethernet frame can be misinterpreted as an IPv4 or IPv6 packet by intermediate P nodes performing ECMP based on deep packet inspection, thus resulting in load balancing packets belonging to the same flow on different ECMP paths and subjecting those packets to different delays. Therefore, packets belonging to the same flow can arrive at the destination out of order. This out-of-order delivery can happen during steady state in the absence of any failures, resulting in significant impact on network operations.

In order to avoid any such misordering, the following rules are applied:

  • If a network uses deep packet inspection for its ECMP, then the "Preferred PW MPLS Control Word" [RFC4385] SHOULD be used with the value 0 (e.g., a 4-octet field with a value of zero) when sending EVPN-encapsulated packets over an MP2P LSP.

  • If a network uses entropy labels [RFC6790], then the control word SHOULD NOT be used when sending EVPN-encapsulated packets over an MP2P LSP.

  • When sending EVPN-encapsulated packets over a P2MP LSP or P2P LSP, then the control word SHOULD NOT be used.

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