6500 VSS and Hot-Sync Standby fabric concept.

[oliv Parcell]

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.

[Shawn Wargo · Accepted solution]

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)...

• VSS  supports a traditional 2 Supervisor (aka Dual-Sup) HA model... as well  as a newer 4 Supervisor (aka Quad-Sup, with 2 Supervisor per VSS  chassis) HA model.
• The VSS Quad-Sup HA model introduces new  terminology, such as In-Chassis Active (ICA) and In-Chassis-Standby  (ICS)... in addition to the traditional SSO Active & Standby  Supervisors.
• VS-S720-10G only supports RPR-WARM between the  ICA & ICS (with SSO between the 2 chassis)... which is commonly  known as "Quad-Sup Uplink Forwarding"
• http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2SX/configuration/guide/vss.html#wp1204229
• Thus, the Sup720 VSS Quad-Sup does NOT support Standby Fabric Hot-Sync (rather, it is N/A).
• VS-S2T-10G  now supports SSO both between the 2 chassis, and between the ICA &  ICS... which is commonly known as "Quad-Sup VSS SSO" or "VS4O".
• http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/15.1SY/config_guide/sup2T/virtual_switching_systems.html#wp1340811
• So... Sup2T with Quad-Sup VSS SSO does (also) support Standby Fabric Hot-Sync!

[oliv Parcell]

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