Alcatel-Lucent 7750 Configuration Manual page 124

LAG and ECMP Hashing
LSR Label-IP Hash Option Enabled
In the first hash round for ECMP, the algorithm will parse down the label stack and once it hits the
bottom it checks the next nibble. If the nibble value is 4 then it will assume it is an IPv4 packet. If
the nibble value is 6 then it will assume it is an IPv6 packet. In both cases, the result of the label
hash is fed into another hash along with source and destination address fields in the IP packet
header. Otherwise, it will just use the label stack hash already calculated for the ECMP path
selection.
If there are more than five labels in the stack, then the algorithm will also use the result of the label
hash for the ECMP path selection.
The second round of hashing for LAG re-uses the net result of the first round of hashing. This
means IPv6 packets will continue to be hashed on label stack only.
LSR IP-Only Hash Option Enabled
This option behaves like the label-IP hash option except that when the algorithm reached the
bottom of the label stack in the ECMP round and finds an IP packet, it throws the outcome of the
label hash and only uses the source and destination address fields in the IP packet's header.
LSR Ethernet Encapsulated IP Hash only Option Enabled
This option behaves like LSR IP only hash except for how the IP SA/DA information is found.
The following conditions are verified to find IP SA/DA for hash.
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L4 Load Balancing
Operator may enable L4 load balancing to include TCP/UDP source/destination port numbers in
addition to source/destination IP addresses in per flow hashing of IP packets. By including the L4
information, a SA/DA default hash flow can be sub-divided into multiple finer-granularity flows if
the ports used between a given SA/DA vary.
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Label stack must not exceed 3 labels deep
After the bottom of the stack is reached, the hash algorithm verifies that what follows is
Ethernet II untagged frame (by looking at the value of ethertype at the expected packet
location whether it contains Ethernet encapsulated IPv4 (0x0800) or IPv6 (0x86DD)
value.
When the ethertype verification passes, the first nibble of the expected IP packet location
is then verified to be 4 (IPv4) or 6 (IPv6).
7750 SR Interface Configuration Guide