Can i use 10G fiber port for fast hello (VSS dual active detection)

[jason_majie]

Hi guys,

need you advise.

i am going to purchase 2 Cat6506 with Sup-2T to run VSS, since all the uplink/downlink are 10G based fiber, and no other 1G connection is required, i really dont want to buy 1G line card.

Of course, ePAGP will be enabled, but cisco suggest to run two methods for dual-active detection, so can i use 10G (from WS-X6816-10G-2T) for fast hello link, or use ePAGP alone will be enough?

thanks

regards

Jason

[Arumugam Muthaiah]

Hi Jason,

Dual-Active Detection

If the VSL fails, the VSS standby chassis cannot determine the state of the VSS active chassis. To ensure that switchover occurs without delay, the VSS standby chassis assumes the VSS active chassis has failed and initiates switchover to take over the VSS active role.

If the original VSS active chassis is still operational, both chassis are now VSS active. This situation is called a dual-active scenario. A dual-active scenario can have adverse affects on network stability, because both chassis use the same IP addresses, SSH keys, and STP bridge ID. The VSS must detect a dual-active scenario and take recovery action.

The VSS supports these three methods for detecting a dual-active scenario:

1. Enhanced PAgP—Uses PAgP messaging over the MEC links to communicate between the two chassis through a neighbor switch. Enhanced PAgP is faster than IP BFD, but requires a neighbor switch that supports the PAgP enhancements.
2. IP Bidirectional Forwarding Detection (BFD)—Uses BFD messaging over a backup Ethernet connection. IP BFD uses a direct connection between the two chassis and does not require support from a neighbor switch.
3. dual-active fast-hello—Uses special hello messages over a backup Ethernet connection. Dual-active fast-hello is faster than IP BFD and does not require support from a neighbor switch. This method is available only in Cisco IOS Release 12.2(33)SXI and later releases,

You can configure all three detection methods to be VSS active at the same time.

Refer:

http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2SX/configuration/guide/vss.html#wp1063913

Regards,

Aru

[Reza Sharifi · Accepted solution]

Hi Jason,

You defiantly can use a port from WS-X6816-10G-2T module you have.  Fast hello could be 1Gig, 10Gig, copper, fiber.  It doesn't matter.  Also, if you are using Fast hello, you really don't need to run ePAGP any more.  It is usually either or and not both.

HTH

[jason_majie]

Thanks Reza, that's very helpful. I plan to use ePAGP alone, using 10G port for fasthello is a bit waisty frankly speeking.