Is it platform specific
broadcom
Importance or Severity
High
Description of the bug
We investigated the issue of the ingress port playing an unexpected role in ECMP egress member selection on our Q3D T2 testbeds.
What we verified on live hardware is that the ECMP hashing behavior is dependent on the 16-bit hash seed stored per (core, PP-port) in IPPB_LB_SEED_MAP_MEM. When different ingress ports have the same seed, the hashing is exactly the same—an identical 5-tuple egresses the same ECMP member regardless of the ingress port or core. Conversely, when the ingress ports have different seeds, the hashing is different, causing the same flow to split deterministically across different ECMP members.
One possible root cause for this ingress port dependence is a non-uniform programming of this seed table due to a defect in the SAI.
BCM CSP CS00012479434
Steps to Reproduce
Same 5 tuple traffic from different ingress port takes different egress port on Q3D
Actual Behavior and Expected Behavior
Same 5 tuple traffic from different ingress port needs to egress out on same port on Q3D
Relevant log output
Output of show version, show techsupport
Attach files (if any)
No response
Is it platform specific
broadcom
Importance or Severity
High
Description of the bug
We investigated the issue of the ingress port playing an unexpected role in ECMP egress member selection on our Q3D T2 testbeds.
What we verified on live hardware is that the ECMP hashing behavior is dependent on the 16-bit hash seed stored per (core, PP-port) in IPPB_LB_SEED_MAP_MEM. When different ingress ports have the same seed, the hashing is exactly the same—an identical 5-tuple egresses the same ECMP member regardless of the ingress port or core. Conversely, when the ingress ports have different seeds, the hashing is different, causing the same flow to split deterministically across different ECMP members.
One possible root cause for this ingress port dependence is a non-uniform programming of this seed table due to a defect in the SAI.
BCM CSP CS00012479434
Steps to Reproduce
Same 5 tuple traffic from different ingress port takes different egress port on Q3D
Actual Behavior and Expected Behavior
Same 5 tuple traffic from different ingress port needs to egress out on same port on Q3D
Relevant log output
Output of
show version,show techsupportAttach files (if any)
No response