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oliv Parcell
Beginner

6500 VSS and Hot-Sync Standby fabric concept.

Hello,

I am preparing an eFSU on our VSS (one SUP720-10G-3C per chassis) and I need some informations about the concept of Hot-Sync Standby fabric

which is not clear enough for me.

I understand that the switch fabric provides a data path for fabric-enabled line cards.

I understand also the FABRIC communication is locally signifiant on a per chassis basis (one chassis - one Sup-720 - multiple fabric channels to the line cards through the Back plane).

When I issue the "show fabric status" I can see Y(hot) which leads me to think there a kind of stateful synchronistation on the FABRICs (one active fabric communication / one Standby).

===================================================

Switch_VSS #show fabric status

slot  channel speed module   fabric   hotStandby  Standby  Standby

                     status   status      support  module   fabric

    1        0   20G     OK       OK       Y(hot)

    1        1   20G     OK       OK      Y(hot)

    5        0   20G     OK       OK          N/A

    5        1   20G     OK       OK          N/A

    7        0   20G     OK       OK      Y(hot)

===================================================

My question is :

In my VSS I have only one SUP720 per chassis. How the "Hot-Sync Standy Fabric" can work on a VSS system as the FABRIC communication is local to a chassis (correct me if I am wrong) => The two SUP FABRICs are ACTIVE in both chassis.

Does this feature is only to consider when we have a ACTIVE/STANDBY SUP in the same 6500 chassis ?

I hope I have been clear enough in my question.

Best regards.

Oliv.


1 ACCEPTED SOLUTION

Accepted Solutions
Shawn Wargo
Cisco Employee

Hi Oliv.

It is now many months since your  post... but I do not normally puruse the Support Community... and so  only just saw it (with no answer)! Alas... this is a somewhat misunderstood & poorly documented feature.

So anyway... here is a brief overview (from the  archives) regarding how the so-called "Standby Fabric Hot-Sync" feature  works, and have highlighted the key points. 

  • The   Hot-Sync Standby fabric feature reduces the switchover time by  bringing  the fabric channels on the standby Supervisor module to a  fully  synchronized state. The fully synchronized state includes sending  clocking signals via the fabric channels.
  • Even  though the Standby  Supervisors' switch fabric is in the Hot-Sync  state, the fabric is still  not used for user data traffic. This simply reduces the time for the  Standby to take over as the Active Supervisor.
  • The  Hot-Sync Standby fabric feature is enabled by default for all 6700-series line cards installed in an E-series chassis running Cisco  IOS Software Release  12.2(33)SXH or newer. No configuration commands are  need to enable this  feature.

http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps708/prod_white_paper0900aecd801c5cd7.html#wp9000058

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

So... with the requisite 6700 or newer Cards, you are now able to acheive ~50-200ms of SSO switchover time!

Note that this ~50ms time is only applicable to the  6708, 6716 and newer Cards (which support a hardware interrupt  signal)... while the 6704, 6724, 6748 Cards (which rely on software  notification) will be able to acheive ~200-300ms.

Now, to answer your questions directly...

Yes, this ONLY applies to 2 x Supervisor (Active/Standby) in the same C6500-E chassis.

Thus... No, it does NOT apply (necessarily) to a VSS with a single Supervisor HA model.

However, I would like to use this opporunity to address a few more questions (that you or others may have)...

View solution in original post

2 REPLIES 2
Shawn Wargo
Cisco Employee

Hi Oliv.

It is now many months since your  post... but I do not normally puruse the Support Community... and so  only just saw it (with no answer)! Alas... this is a somewhat misunderstood & poorly documented feature.

So anyway... here is a brief overview (from the  archives) regarding how the so-called "Standby Fabric Hot-Sync" feature  works, and have highlighted the key points. 

  • The   Hot-Sync Standby fabric feature reduces the switchover time by  bringing  the fabric channels on the standby Supervisor module to a  fully  synchronized state. The fully synchronized state includes sending  clocking signals via the fabric channels.
  • Even  though the Standby  Supervisors' switch fabric is in the Hot-Sync  state, the fabric is still  not used for user data traffic. This simply reduces the time for the  Standby to take over as the Active Supervisor.
  • The  Hot-Sync Standby fabric feature is enabled by default for all 6700-series line cards installed in an E-series chassis running Cisco  IOS Software Release  12.2(33)SXH or newer. No configuration commands are  need to enable this  feature.

http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps708/prod_white_paper0900aecd801c5cd7.html#wp9000058

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

So... with the requisite 6700 or newer Cards, you are now able to acheive ~50-200ms of SSO switchover time!

Note that this ~50ms time is only applicable to the  6708, 6716 and newer Cards (which support a hardware interrupt  signal)... while the 6704, 6724, 6748 Cards (which rely on software  notification) will be able to acheive ~200-300ms.

Now, to answer your questions directly...

Yes, this ONLY applies to 2 x Supervisor (Active/Standby) in the same C6500-E chassis.

Thus... No, it does NOT apply (necessarily) to a VSS with a single Supervisor HA model.

However, I would like to use this opporunity to address a few more questions (that you or others may have)...

Hello Shawn,

Many thanks for the complete and very intersting answer, It was worth waiting

Thanks as well for the additional information regarding the differences between "Quad-Sup Uplink Forwarding" and "VS4O".

Regards.

Oliv