Alcatel-Lucent 7750 Configuration Manual page 126

LAG and ECMP Hashing
Enhanced Multicast Load Balancing
Enhanced multicast load balancing allows operators to replace the default multicast per flow hash
input (internal multicast ID) with information from the packet. When enabled, multicast traffic for
Layer 3 services (such as IES, VPRN, r-VPLS) and ng-MVPN (multicast inside RSVP-TE, LDP
LSPs) are hashed using information from the packet. Which inputs are chosen depends on which
per flow hash inputs options are enabled based on the following:
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NOTE: Enhanced multicast load balancing requires minimum chassis mode D. It is not
supported with Layer 2 and ESM services. It is supported on 7750 SR (excluding c4/c12)
platforms.
Security Parameter Index (SPI) Load Balancing
IPSec tunnelled traffic transported over LAG typically falls back to IP header hashing only. For
example, in LTE deployments, TEID hashing cannot be performed because of encryption, and the
system performs IP-only tunnel-level hashing. Because each SPI in the IPSec header identifies a
unique SA, and thus flow, these flows can be hashed individually without impacting packet
ordering. In this way, SPI load balancing provides a mechanism to improve the hashing
performance of IPSec encrypted traffic.
SR OS allows enabling SPI hashing per L3 interface (this is the incoming interface for hash on
system egress)/L2 VPLS service. When enabled, an SPI value from ESP/AH header is used in
addition to any other IP hash input based on per-flow hash configuration: source/destination IPv6
addresses, L4 source/dest ports in case NAT traversal is required (l4-load-balancing is enabled). If
the ESP/AH header is not present in a packet received on a given interface, the SPI will not be part
of the hash inputs, and the packet is hashed as per other hashing configurations. SPI hashing is not
used for fragmented traffic to ensure first and subsequent fragments use the same hash inputs.
SPI hashing is supported for IPv4 and IPv6 tunnel unicast traffic and for multicast traffic (mc-enh-
load-balancing must be enabled) on all platforms and requires L3 interfaces or VPLS service
interfaces with SPI hashing enabled to reside on IOM3-XP or newer line-cards.
Page 126
IP replication—The hash algorithm for multicast mimics unicast hash algorithm using SA/
DA by default and optionally TCP/UDP ports (Layer 4 load balancing enabled) and/or
system IP (System IP load balancing enabled) and/or source/destination parameters only
(Source-only/Destination-only hash inputs).
MPLS replication—The hash algorithm for multicast mimics unicast hash algorithm
described in LSR Hashing on page 122.
7750 SR Interface Configuration Guide