VSS and 10Gb module performance mode

[StevieOliver_2]

Hi

On http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps708/qa_cisco_catalyst_6500_series_16port_10gigabit_ethernet_module.html

it states that if you put the 16 port card into performance mode only 4 ports are useable.  If I read correctly then to use the 16 port card for VSL it needs to be in performance mode and hence we lose 12 ports.

With the 8 port card it says on http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps708/product_data_sheet09186a00801dce34.html

8-Port 10 Gigabit Ethernet Fiber Module

The 8-port 10 Gigabit Ethernet fiber module (Figure 3) provides up to 66 10 Gigabit Ethernet ports in a single Cisco Catalyst 6509 chassis and 132 10 Gigabit Ethernet ports in a VSS. It supports 64 Gbps of local switching, making it ideal for deployment in the core or aggregation layer of LAN campuses and data centers. All 8 ports can be used to create a virtual switch link in a VSS.

This implies that even though the 8 port module is oversubscribed 2:1 it need not be in performance mode to be used for the VSL.  So buy an 8 port card for VSL and you keep all 8 ports but buy a 16 port card and you need to disable 12 ports to be able to use it for VSL.

While I do not need to use all 8 ports on the 8 port card for VSL I want to use one port and have the remaining 7 also available for other uses. 

It seems strange that the 16 port card needs to be in a mode that disables 12 ports but the 8 port card does not.

Am I missing something here ?

Thanks, Stephen.

[Reza Sharifi · Accepted solution]

Hi Stephen,

Your understanding is correct.  With the 16 port line card you have the capability to disable 3 ports in each group and use one port in performance mode, but the same scenario does not apply to the 8 port.  You can also use the 2 10Gig ports on the sup module for your VSL link.  It is actualy recommended:

From the config guide:

We recommend that you use both of the 10-Gigabit  Ethernet ports on the supervisor engines to create the VSL between the  two chassis.

For more info refer to this link:

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

HTH

.

[StevieOliver_2]

Many thanks Reza.

It seems strange to me that the 16 port card must be put in non-oversubscribed (performance) mode but the 8 port can be used in 2:1 oversubscribed mode.  So we are better off using a cheaper 8 port card if we deploy the VSL on it.

I'm also puzzled about the Cisco recommendation to put the VSL across the 2 Sup720 ports in each chassis.  If the standby Sup720 fails then the VSL fails and a whle chassis is lost.

Am I correct in thinking if we split the VSL across a Sup720 and an 8 port card then the VSS can sustain both chassis if the standby Sup720 fails ?  The standby Sup goes down but since it only accommodates one of the two VSL ports then the VSL survives via the 8 port module and the cards in the standby chassis stay up (???) Or do the standby chassis modules go down and stay down if their Sup fails ?

Thanks again, Stephen.

[Reza Sharifi]

Hi Stephen,

You definably better off using the 8 port module.  BTW, with the new Sup 2T, all ports for this module will be line rate since  per slot capacity will be increased to 80 Gig now.

I'm also puzzled about the Cisco recommendation to put the VSL across  the 2 Sup720 ports in each chassis.  If the standby Sup720 fails then  the VSL fails and a whle chassis is lost.

It really doesn't mater, because this is always the case.  When the Sup fails, the whole chassis including the line cards are dead. That is why, it is recommendation to use VSS  data centers where you can uplink your servers to both switches, or in a distro /core layer where you can duly uplink you access layer switches to both chassis.

Am I correct in thinking if we split the VSL across a Sup720 and an 8  port card then the VSS can sustain both chassis if the standby Sup720  fails ?  The standby Sup goes down but since it only accommodates one of  the two VSL ports then the VSL survives via the 8 port module and the  cards in the standby chassis stay up (???) Or do the standby chassis  modules go down and stay down if their Sup fails ?

No, regardless of how you connect you VSL ports, when the Sup fails, the entire device is dead. That is common misunderstanding with VSS.  A lot of people think, if for example the Sup in chassis-A (primary) fails, the backup Sup in chassis-B will take over and manage chassis-A, but this is not the case.

HTH

[Leo Laohoo]

So we are better off using a cheaper 8 port card if we deploy the VSL on it.

Unless you plan to upgrade from Sup720 to Sup2T, I would NOT recommend using the 8-port because this line card is NOT compatible to the Sup2T.