Alcatel-Lucent 7710 SR OS, Руководство по настройке интерфейса

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Interface Configuration
7710 SR OS Interface Configuration Guide Page 77
LSR Label-IP Hash Option Disabled
This section discusses the behavior of ECMP and LAG hashing at an LSR.
1. The ECMP hash consists of an initial hash based on the source port/system IP address. Each
label in the stack is then hashed separately with the result of the previous hash, up to a maxi-
mum of 5 labels.
2. Then, the net result is used to select which LDP FEC next-hop to send the packet to using a
modulo operation of the net result with the number of next-hops. If there is a single next-hop
for the LDP FEC, or if the packet is received on an RSVP LSP ILM, then a single next-hop
exists.
This same net result will feed to a second round of hashing if there is LAG on the egress port
where the selected LDP or RSVP LSP has its NHLFE programmed.
LSR Label-IP Hash Option Enabled
When the LSR label-IP hash option is enabled, the new hash routine is still limited to a label stack
of 5.
1. In the first hash round for ECMP, the algorithm parses 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’s header.
Otherwise, it will use the label stack hash already calculated for the ECMP path selection. If
there are more than 5 labels in the stack, then the algorithm will also use the result of the
label hash for the ECMP path selection.
2. The second round of hashing for LAG re-uses the net result of the first round of hashing.