STP & RSTP

[k_srinadh]

What is the difference between STP & RSTP ?

(Except Speed of convergence when topology changes..)

Any Specific diffeences…

Thanks & Regards,

Srinadh Kodali

[minumathur]

Hi

In STP everything is based on timer ( forward delay ( 15), max-age timer -20 second), when timer expired Network start reconvergance.

The main difference in RSTP is that all bridges can send BPDU, not jsut the root.

So in the instance of a switch goes down, any switch that has a link connected to it will notice (as its link has gone down) this switch will then bring up its alternitive port and send out a BPDU to nebiour switchs still alive to say it has done so. (so no timer need to time out, this happens almost instancley). this BPDU then travel through the network update all other switchs resulting in sub second fail over and covergence of the network.

-Minu

[Peter Paluch]

Hi,

This is a very good article describing the most important changes in the RSTP machinery. Check it out!

http://www.cisco.com/en/US/tech/tk389/tk621/technologies_white_paper09186a0080094cfa.shtml

Best regards,

Peter

[Ganesh Hariharan · Accepted solution]

What is the difference between STP & RSTP ?
(Except Speed of convergence when topology changes..)
Any Specific diffeences… 
Thanks & Regards,
Srinadh Kodali

Hi Srinadh,

In stable topology only the root sends BPDU and relayed by others in STP and in RSTP In stable topology all bridges generate BPDU every Hello (2 sec) : used as “keepalives” mechanism.

Port state in STP are Disabled,Blocking,Listening,Learning,Forwarding and in RSTP Discarding (replace disabled, blocking and listening),Learning,Forwarding.

Port Roles in STP Root (Forwarding),Designated (Forwarding),Non-Designated (Blocking) and in RSTP Root (Forwarding),Designated (Forwarding),Alternate (Discarding),Backup (Discarding)

Additional configuration to make an end node port a port fast (in case a BPDU is received) and in RSTP An edge port (end node port) is an integrated Link type which depends on the duplex : Point-to-point for full duplex & shared for half duplex).

Topology changes convergence in STP is Use timers for convergence (advertised by the root):Hello (2 sec),Max Age (20 sec),Forward delay timer (15 sec) and in RSTP you have Introduce proposal and agreement process for synchronization (< 1 sec).- Hello, Max Age and Forward delay timer used only for backward compatibility with standard STP   Only RSTP port receiving STP (802.1d) messages will behaves as standard STP.

Slow transition in STP with (50sec):Blocking (20s) =>Listening (15s) =>Learning (15s) =>Forwarding  and in RSTP Faster transition on point-to-point and edge ports only:Less states – No learning state, doesn’t wait to be informed by others, instead, actively looks for possible failure by RLQ (Request Link Query) a feedback mechanism.

Hope to Help !!

Ganesh.H

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