MSTP vs RSTP

[PEI_1]

Hi,
I read about MSTP from 2610-AdvTrafficMgmt-Dec2007-59918641.pdf that MSTP needs at least one instance, the default IST and MSTI is optional.

If a MSTP contains only IST with no other MSTI, what is the difference to RSTP (as RSTP only has one instance)?

How do I determine how many MST regions should I have? Can I configure region?

Can RSTP support multiple regions?

Thank you.
Pei

[Richard Brodie_1]

it's easier to take your questions backwards:

The whole of a MSTP region acts like a black box containing a single RSTP system.

So the answer to your last question is yes. It's single regions that it doesn't support.

You put two MSTP systems in the same region by giving them the same configuration name, revision, VLAN to instance mappings. Otherwise they will all be in unique regions and work just like RSTP.

If you don't actually need multiple spanning tress, then its probably not worth setting up a common configuration.

"If a MSTP contains only IST with no other MSTI, what is the difference to RSTP?"

RSTP only understands the CST.

[PEI_1]

Thanks for your reply. Please help to explain below:

it's easier to take your questions backwards:

The whole of a MSTP region acts like a black box containing a single RSTP system.

So the answer to your last question is yes. It's single regions that it doesn't support.

Q:What do you mean here by "It's single regions that it doesn't support"? Do you mean RSTP can/can't support multiple regions?

You put two MSTP systems in the same region by giving them the same configuration name, revision, VLAN to instance mappings. Otherwise they will all be in unique regions and work just like RSTP.

Q:Beside configuring the MSTI name, revision and VLAN to instance mappings, do I have to configure the switches to which region they belong?

If you don't actually need multiple spanning tress, then its probably not worth setting up a common configuration.
Q: What do you mean by setting up a common configuration.
Q: If I have multiple VLANs, how do i decide if it is better to have MSTP or RST?

"If a MSTP contains only IST with no other MSTI, what is the difference to RSTP?"

RSTP only understands the CST.
Q:Do you mean RSTP only understand CST therefore it cannot support multiple regions?

[Richard Brodie_1]

Q:What do you mean here by "It's single regions that it doesn't support"? Do you mean RSTP can/can't support multiple regions?

You can't put RSTP switches in an MSTP region. They are each in their own individual region.

Q:Beside configuring the MSTI name, revision and VLAN to instance mappings, do I have to configure the switches to which region they belong?

No.

Q: What do you mean by setting up a common configuration.

If you just leave the default unique config names, everything will be in separate regions, as if you were running RSTP.

Q: If I have multiple VLANs, how do i decide if it is better to have MSTP or RST?

The main thing you gain by is active-active load-balancing as well as failover. The question is whether you care enough that some of the links you've paid for are blocking most of the time.

Q:Do you mean RSTP only understand CST therefore it cannot support multiple regions?

No, CST is what happens between regions. You can't put an RSTP switch into a region.

A way of thinking of an MSTP region is a cluster of machines that provide an RSTP service. From an external client's point of view it looks like a single RSTP node. You can't add an a RSTP node to a cluster because it doesn't support the cluster's internal communication protocol (the IST). Is that a better analogy?

[PEI_1]

Hi Richard
I have attached a picture with 2 setup of MSTP (figure 1 and figure 2), each containing 3 Procurve 2610 switches.

Figure 1: The MSTP has only one region with only IST, so all VLANs belong to this IST.

Figure 1a: With RSTP, all VLANs belong to the same instance.

Q: configuring MSTP with only a default IST has the same result as configuring the 3 switches with RSTP?

Figure 2: The MSTP contains IST (VLAN1,10) and a MSTI (VLAN20). Switch5 is the root switch, and root for IST. Switch3 is the root for MSTI.

Please advise if the MSTP configuration for priority is right as per Figure 2.

Thanks
Pei