MSTP

[skhargotre]

Dear All.

We r trying to design the Network with 50 Switches in single chain and 50th switch back to 1st switch. the 50 switch will ahve 50 Vlans.
Can we do with MSTP using multiple instance and each instance using for 10 Vlan.

Regards.
Santosh.

[Olaf Borowski]

Santosh,

do you really mean 50 switches in a "ring" topology? Aside from MSTP, there are guidelines in the IEEE spec. that specify how many hops are recommended. 50 is too much!

[Ardon]

Hi Santosh,

Indeed, like Olaf states, 50 is too much. MSTP (802.1s) per default has a maximum hopcount of 20 and by making a PURE ring topology you would exceed that number. You have to look for a physical topology that is more cross link (making a kind of s spider web). However, in the WORST case scenario when all inside links fail and the only path left is the outer ring, you will still trespass the 20 hop rule.

The maximum value you can set for the hop count is 40 (see the Advanced Traffic and Management Guide). Mind you that this maximum is WITHIN a MSTP Region:

'spanning-tree max-hops < hop-count >
This command resets the number of hops allowed for BPDUs in an MST region. When an MSTP switch receives a BPDU, it decrements the hop-count setting the BPDU carries. If the hop-count reaches zero, the receiving switch drops the BPDU. Note that the switch does not change the message-age and maximum-age data carried in the BPDU as it moves through the MST region and is propagated to other regions. (Range: 1
-40; Default: 20'

Not knowing you expertise in designing networks please be reminded that a network consisting of 50 switches with 50 VLANs (divided into 5 MSTI's) requires very proper preperation and testing before implementing it into a live network. I am not even mentioning the fact of adding other spanning tree parameters like: BPDU Protection, BPDU Filtering and Root Guard Protection.

What I see a lot is that people like to prune certain VLANs on physical or logical (Trunk) links. No problem if ones knows exactly what they are doing and what happens in case a Designated or Root port fails and a Backup (Alternate/Discarding) has to go into Forwarding. There is a high risk of orphaning certain VLANs in case of a link failure in the latter (VLANs pruned scenario).

Good Luck

[skhargotre]

Dear All.

Kindly find the network diagram for the query.

Regards.
Santosh.

[Ardon]

Nice that diagram. So now you want people to earn you money and design that network?

Sleep well.

[skhargotre]

Dear all.

Thanks.....

Regards.
Santosh.