Best practice for VSL

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Nov 15th, 2009
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There is one Supervisor Engine 720-10G VSS (VS-S720-10G-3C/XL) and one Cisco 8-Port 10 Gigabit Ethernet Switching Module (WS-X6708-10G-3C/XL) in each Catalyst 7609. I can use two 10G for the VSL. What is the best practice for 10G to be used for VSL; either from the SUP720 or 10G Switching Module? Please reply with the justification of your recommendation.

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Giuseppe Larosa Sun, 11/15/2009 - 22:40
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Hello Muhammad,

I would deploy a VSL using one link from WS6708 and one from supervisor.

the reason to use at least one link from WS 6708 is that in case of supervisor failure the other supervisor has still a chance to control the other chassis.

I would consider to use a third link taken from WS 6708.


I would also deploy a direct GE link for active/active detection using both BFD and fast hellos.


see


http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2SX/configuration/guide/vss.html#wp1063892


Hope to help

Giuseppe


Ahmed Shahzad Mon, 11/16/2009 - 13:41
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Hi Giuseppe,


Thank you for your email. Since each Catalyst in VSS having on SUP, and in case SUP gets failed then how come WS6708 would be working, and other Catalyst detect it.


Thanks and Regards,

Shahzad.

Giuseppe Larosa Mon, 11/16/2009 - 13:58
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Hello Shahzad,

my understanding of VSS is that VSL bundle is not used only to exchange user traffic frames.


VSL is used to carry on proprietary encapsulated frames also control plane messages to form a single device.


one supervisor the active one controls both chassis with second supervisor acting as hot standby as in a single chassis with two supervisors.


There is clearly a limitation in available bw between the two chassis but 20 Gbps are enough to allow control of standby chassis linecards by active supervisor.


until most user traffic is confined in a single chassis this approach works and allows to form multichassis etherchannels with access layer switches using both uplinks at the same time.


Hope to help

Giuseppe


Ahmed Shahzad Mon, 11/16/2009 - 14:07
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Hi Giuseppe,


With your statement I assume that if we have VSL link comprises of one from SUP and other from switching card, and if one of the SUP failed, still the VSS would work fine for line card on both Chassis. Please reply that how it works without the SUP on chassis? I was in believe that if SUP failed, VSS would also get failed.


Thanks and Regards,

Shahzad.

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