Let me explain my topology:
two 6506's in VSS
I have a layer 2 vlan on the production network that connects the lab network (6509) via a 1gb fiber connection
a 4507 with a 20gb port channel to the VSS
What I am doing:
Moving a large file from the production environment to the lab environment. So, in the production environment, I copied a large file (30gb vmdk from vmware) to a laptop. It copied fairly quickly. So, I then take that laptop and move it to a different port on my switch that is on layer 2 vlan connected to the lab 6509 to upload the same file to the vmware server in the lab. And now the copy is SLOWWW!
in looking at the network during this copy, I am not seeing any bandwidth saturation on any links, specifically the 1gb link between the 6506 to the 6509. That link is currently at about 3 - 4.7% (according to my Fluke) Also, I am seeing a large amount of giants on the VSL interface on one of the 6506's. That's telling me that the traffic is having to traverse this VSL interface in order to get to the 6509 in the lab.
According to one of the cisco documents, it was saying that the amount of giants increasing on a VSL interface is normal. Maybe so, but I can't help but think that this is the reason why the copy is going so much slower. Any thoughts on this? Could this be why the file copy is so slow?
Thanks!
I think it is because frames forwarded over the VSL link are encapsultated with a special 32byte header(giants). I looked the same in our VSS too, but we are not detecting perfomance issues.
Traffic on the VSL
The VSL carries data traffic and in-band control traffic between the two chassis. All frames forwarded over the VSL link are encapsulated with a special 32-byte header, which provides information for the VSS to forward the packet on the peer chassis.
The VSL transports control messages between the two chassis. Messages include protocol messages that are processed by the VSS active supervisor engine, but received or transmitted by interfaces on the VSS standby chassis. Control traffic also includes module programming between the VSS active supervisor engine and switching modules on the VSS standby chassis.
The VSS needs to transmit data traffic over the VSL under the following circumstances:
•
Layer 2 traffic flooded over a VLAN (even for dual-homed links).
•Packets processed by software on the VSS active supervisor engine where the ingress interface is on the VSS standby chassis.
•The packet destination is on the peer chassis, such as the following examples:
–Traffic within a VLAN where the known destination interface is on the peer chassis.
–Traffic that is replicated for a multicast group and the multicast receivers are on the peer chassis.
–The known unicast destination MAC address is on the peer chassis.
–The packet is a MAC notification frame destined for a port on the peer chassis.
VSL also transports system data, such as NetFlow export data and SNMP data, from the VSS standby chassis to the VSS active supervisor engine.
To preserve the VSL bandwidth for critical functions, the VSS uses strategies to minimize user data traffic that must traverse the VSL. For example, if an access switch is dual-homed (attached with an MEC terminating on both VSS chassis), the VSS transmits packets to the access switch using a link on the same chassis as the ingress link.
Traffic on the VSL is load-balanced with the same global hashing algorithms available for EtherChannels (the default algorithm is source-destination IP).
