White Papers

Command
History
Version Description
9.9(0.0) Introduced on the FN IOM. Added flow-based-hashing support for hashing on
ECMP.
9.2(0.0) Introduced on the MXL 10/40GbE Switch IO Module.
Usage
Information
To ensure that CRC is not used for LAG, set the default hash-algorithm method on ExaScale systems. For
example,hash-algorithm ecmp xor lag checksum nh-ecmp checksum.
To achieve the functionality of hash-align on the ExaScale platform, do not use CRC as a hash-algorithm
method.
The hash value calculated with the hash-algorithm command is unique to the entire chassis. The hash
algorithm command with the line card option changes the hash for a particular line card by applying the
mask specified in the IPSA and IPDA fields.
The line card option is applicable with the lag-hash-align microcode only (refer to CAM Profile
Commands). Any other microcode returns an error message as follows:
● Dell(conf)#hash-algorithm linecard 5 ip-sa-mask ff ip-da-mask ff
● % Error: This command is not supported in the current microcode
configuration
In addition, the linecard number ip-sa-mask value ip-da-mask value option has the
following behavior to maintain bi-directionality:
● When hashing is done on both IPSA and IPDA, the ip-sa-mask and ip-da-mask values must be
equal. (Single Linecard).
● When hashing is done only on IPSA or IPDA, the Dell Networking OS maintains bi-directionality with
masks set to XX 00 for line card 1 and 00 XX for line card 2 (ip-sa-mask and ip-da-mask). The
mask value must be the same for both line cards when using multiple line cards as ingress (where XX
is any value from 00 to FF for both line cards). For example, assume that traffic is flowing between
linecard 1 and linecard 2:
● hash-algorithm linecard 1 ip-sa-mask aa ip-da-mask 00
● hash-algorithm linecard 2 ip-sa-mask 00 ip-da-mask aa
The different hash algorithms are based on the number of Port Channel members and packet values. The
default hash algorithm (number 0) yields the most balanced results in various test scenarios, but if the
default algorithm does not provide a satisfactory distribution of traffic, use the hash-algorithm command
to designate another algorithm.
When a Port Channel member leaves or is added to the Port Channel, the hash algorithm is recalculated
to balance traffic across the members.
On TeraScale, if you do not enter the keyword ECMP or LAG, the Dell Networking OS assumes it to be
common for both. If the keyword ECMP or LAG is entered separately, both should fall in the range of 0 to
23 or 24 to 47 since compression enable/disable is common for bothTeraScale and ExaScale support the
range 0-47. The default for ExaScale is 24.
hash-algorithm ecmp
Change the hash algorithm used to distribute traffic flows across an ECMP (equal-cost multipath routing) group.
Syntax
hash-algorithm ecmp {crc-upper} | {dest-ip} | {lsb}
To return to the default hash algorithm, use the no hash-algorithm ecmp command.
Parameters
crc-upper Uses the upper 32 bits of the key for the hash computation. The default is crc-
lower.
dest-ip Uses the destination IP for ECMP hashing. The default is enabled.
lsb Returns the LSB of the key as the hash. The default is crc-lower.
Defaults
● crc-lower
● dest-ip enabled
422 Equal Cost Multi-Path (ECMP)