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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


Description (partial)

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.

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

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