backbone fast, rlq request and rlq reply, timeout value.

[sarahr202]

Hi everybody.

Let suppose our switch receives an inferior bpdu on its current root port. Our sw starts sending RLQ out of its all blocked ports.

My question is how long a switch waits for a RLQ reply on these blocked ports ? ( obviously sw can not wait forever for these RLQ  replies, there ought to  be some timeout value).

As usual have a great weekend.

[Rolf Fischer]

Hi,

I think the process has to stop at the latest when MAX_AGE expires.

If you search for patent US 6219739, you can find a lot of information about the mechanisms.

Best regards

Rolf

[Reza Sharifi · Accepted solution]

Hi Sarah,

From the spanning tree document:

Reacting to Indirect Link Failures

When an inferior BPDU is detected on a non-designated port, the second       phase of backbone fast is triggered. Instead of passively waiting max_age to       age out ports that can be affected by the failure, a proactive way to test them       immediately is introduced by means of the RLQ PDU. The RLQ is used to achieve a       kind of ping for the root on a non-designated port and allowed to quickly       confirm if the BPDU stored on a port is still valid or needs to be discarded.

So, I would say the switch replies to the RLQ immediately.

here is the doc:

http://www.cisco.com/en/US/tech/tk389/tk621/technologies_tech_note09186a00800c2548.shtml

HTH

Have a nice weekend

[sarahr202]

Hi Reza

what if the rlq reply is lost or filtered.then how long a switch waits for rlq reply before giving up?

have a great weekend.