Giant frames on VSL link

Unanswered Question
Sep 29th, 2010

Hi all,

Hi have setup a vss system and i 'am detecting giant hits on the vsl link, could this giant frames be normal traffic that needs tto cross the VSL link ?

on the show port-channel the mtu appears with 9216.


I have this problem too.
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Reza Sharifi Wed, 09/29/2010 - 05:46


If VSS set up correctly data traffic should not be going over the VSL link.  There is usually minimum control traffic that goes over it, but that is not a lot of traffic.  Did you enable jumbo frame on the VSL link?



danrya Wed, 09/29/2010 - 08:48

The VSL link will have an MTU of 9216 and shouldn't be changed.  And there could be data traffic that traverses the VSL.  The VSS system tries to forward packets through locally connected interfaces first, but this is not always possible.  For example, a packet from one host in a vlan to another might traverse the VSL if they are physically connected to different chassis.  Also, packets coming in through an etherchannel might be destined to a host on the other chassis.

Also, all "Control traffic" from any protocols will be processed on the "active" supervisor.  So if it's received on the standby chassis, it will traverse the VSL link.  Take a look at the VSS configuration guide:

The port ASIC will increment this counter for any packet larger than 1518 bytes.  All packets that traverse the VSL link will have a 32 byte header added to the packet.  If the packet is close to the 1518 limit already, it will be considered a "giant".



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