Avaya 8600 Configuration Manual page 13

R, RS, and 8800 module traffic distribution algorithm
This release uses an enhanced traffic distribution algorithm for R, RS, and 8800 modules,
which ensures proper traffic distribution in all customer networks. The MLT hashing algorithm
is based on Layer 4 fields for IPv4 UDP/TCP traffic for R, RS, and 8800 modules, versus Source
and Destination IP addresses. This hash change provides a better distribution of traffic for
many environments, with no impact on module performance. MLT hashing for any module type
is determined at the ingress port, although the affect is seen at the egress MLT. That is, the
traffic ingressing a port determines the destination is an MLT and sends the traffic to the
correctly hashed MLT port, regardless of MLT port type or even a mixed port type. Therefore
in a mixed chassis, the algorithm used is based on ingress port for the traffic, not the MLT
configuration. The new hash algorithm for IPv4 TCP/UDP traffic is as follows:
64-bit key = (SrcPort (16 bits), DstPORT (16 bits), DstIP (LSB 16 bits), SrcIP (LSB 16 bits))
For non TCP/UDP IPv4 traffic:
64-bit key = (DstIP (32 bits), SrcIP (32 bits))
The 64-bit key result is used as an index to a table populated with active MLT ports repeated
over 63 entries.
The CLI command config sys set hash-calc getmltindex is modified to allow src-
port and dst-port as optional parameters. This parameter will provide the transmit or egress
MLT index or port for ingress traffic.
Note that the new hashing for IP traffic between a given source and destination IP address will
be different for TCP/UDP packets and ICMP packets. Therefore, you cannot use the ping-
snoop feature to reliably determine the hashed path taken by IP TCP/UDP traffic when
performed on an ingress port.
The enhanced hash algorithm does not apply to IPv6 traffic, just IPv4. The distribution algorithm
for IPv6 traffic (bridged or routed) is:
• 64-bit key = (SrcIP[63:0] XOR srcIpIp[127:64])
• 64-bit key = ((64-bit key) XOR DestIp[63:0])
• 64-bit key = ((64-bit key) XOR DestIp[127:64])
The distribution algorithm enhancement for other types of IPv6 traffic is to form a 64-bit hash
key using the lower 32 bits of the DestMAC field and the lower 32 bits of the SrcMAC field:
64-bit key = hash(64-bit key, hashFcn)
where hash is a Remote Service Provider (RSP) instruction and hashFcn produces a 6-bit
result. The hash function is 0x000c00003f000000, which contains a 25-bit seed, a 24-bit hash
polynomial coefficient, and a 5-bit polynomial width.
The 64-bit key result is used as an index to a table populated with active MLT ports repeated
over 63 entries.
Configuration — Link Aggregation, MLT, and SMLT
MultiLink Trunking
January 2012 13