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Cisco Bug: CSCum97745 - Nexus 3064 l2 load balancing issue for src/dst port

Last Modified

Mar 16, 2016

Products (6)

  • Cisco Nexus 3000 Series Switches
  • Cisco Nexus 3064 Switch
  • Cisco Nexus 3016 Switch
  • Cisco Nexus 3064-T Switch
  • Cisco Nexus 3048 Switch
  • Cisco Nexus 3132Q Switch

Known Affected Releases

6.0(2)U2(1)

Description (partial)

Symptom:
Load balancing for traffic changing just destination port is not balanced appropriately on Nexus 3064. For an application choosing consecutive destination ports, the hash algorithm associates one link with a pair of 64 ports (in case of a 2 PO link). 32 consecutive ports are associated with one link in case of 4 links PO. This should be more granular.


The particular application opens 16 HTTP flows and downloads from a server hosted in the provider's network (the server has 10G uplinks).
 
The 16 HTTP flows are opened by the host ? the TCP/IP stack of the host is responsible to allocate local ports.
If we think how the traffic is flowing from the switch perspective we have 16 flows with src-port 80 and as destination 16 consecutive ports. Also, src and dst IP addresses are the same at all times.
 
This traffic is then balanced over 2 or 4 1G links between the switch and a BRAS (those links already carry other customers traffic).
Because all flows are hashed on only one link, the total throughput will be 1G ? existing traffic on that link.

Conditions:
no special conditions, it can be reproduced easily.
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Bug Details Include

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