timers in rstp,qos tcam,security acl

Answered Question
Sep 23rd, 2008

hi every body!

I have few question:

1)Should the timer setting such as hello time, max-age time, etc be configured on root bridge or they can be configured independenly on each switch in rstp network ?

2) Can two switches have different hello time or max time in rstp?

3)A mulilayer switch store security acl and qos acl in tcam . My question is are they put in different tcams i.e secuirty acl in tcam while qos acl in other tcam?

thanks a lot!

I have this problem too.
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Correct Answer by Francois Tallet about 8 years 2 months ago

1) you can configure different value, but the root timers setting are used. It makes sense to configure similar timer values on the backup root.

Note also that in MST (I don't remember if this is the case in RSTP in fact), the hello timer is now a local value driven by the designated port. On a given segment, all bridges use the hello-time advertised by the designated port. In theory, we should be able to configure the hello-time on a per-port basis. We did not implement the CLI in IOS (we did in CatOS).

2) yes with MST for the hello-time, as mentioned above. Max age is still driven by the root.

3) no clue;-)

Regards,

Francois

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satish_zanjurne Tue, 09/23/2008 - 21:01

Hi,

BPDU are sent every hello-time, and not simply relayed anymore. With 802.1D, a non-root bridge only generates BPDUs when it receives one on the root port. In fact, a bridge relays BPDUs more than it actually generates them. This is not the case with 802.1w. A bridge now sends a BPDU with its current information every seconds (2 by default), even if it does not receive any from the root bridge

A bridge considers that it loses connectivity to its direct neighbor root or designated bridge if it misses three BPDUs in a row

So if necessary to tune the timers in RSTP, you need to tune on all switches/bridges.

They need to be same on all switches for smooth operation of RSTP.

i think they are in same TCAM.

HTH..rate if helpful..

Correct Answer
Francois Tallet Wed, 09/24/2008 - 08:04

1) you can configure different value, but the root timers setting are used. It makes sense to configure similar timer values on the backup root.

Note also that in MST (I don't remember if this is the case in RSTP in fact), the hello timer is now a local value driven by the designated port. On a given segment, all bridges use the hello-time advertised by the designated port. In theory, we should be able to configure the hello-time on a per-port basis. We did not implement the CLI in IOS (we did in CatOS).

2) yes with MST for the hello-time, as mentioned above. Max age is still driven by the root.

3) no clue;-)

Regards,

Francois

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