LAN Routing

Multiple Spanning Tree in Large Networks

 
ABZ78
Occasional Advisor

Multiple Spanning Tree in Large Networks

Suppose you have 300+ switches in a network. 

The network consists of 1 core router, and 29 remote routers (1 per remote site).

All remote sites are connected to the core router via dark fibre.

All remote sites obtain DHCP, DNS, Internet, etc via the core router.

All switches have MSTP enabled.

My question is what is best practice for rolling out MSTP for a large network like this?

My thoughts are: Set all routers (core and remote) as priotity 0, and each hop from those routers +4k.

However I am confused because won't bpdu packets get sent over the dark fibre to each remote site?

Thoughts?

2 REPLIES 2
parnassus
Honored Contributor

Re: Multiple Spanning Tree in Large Networks

Hi @ABZ78 with 1 core site and 29 satellite sites I would also consider to have a routed network topology (each site is routed to the Core and the Core is the router for all sites) so each site (core included) could eventually have its own Spanning Tree and it stays local on the site. Is it reasonable?

Edit: clearly that would be possible under the assumption you can plan IP Addressing, VLAN and IP Routing accordingly (sort of an Hub and Spoke scenario)...I believe it could be a quite robust deployment strategy.


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ABZ78
Occasional Advisor

Re: Multiple Spanning Tree in Large Networks

Thank @parnassus 

Consider the following (using two routers to keep it simple) 

Both SVI are untagged VLAN 3

Core Rotuer SVI 10.200.5.1   255.255.255.252     <------->  Remote Site 1 Router SVI 10.200.5.2   255.255.255.252

When I set each router to spanning tree priority "0", the following is each routers output


Core-Router# sh span

Multiple Spanning Tree (MST) Information

STP Enabled : Yes
Force Version : MSTP-operation
IST Mapped VLANs : 1-4094
Switch MAC Address : b88303-415600
Switch Priority : 0
Max Age : 20
Max Hops : 20
Forward Delay : 15

Topology Change Count : 8
Time Since Last Change : 22 hours

CST Root MAC Address : b88303-415600
CST Root Priority : 0
CST Root Path Cost : 0
CST Root Port : This switch is root

IST Regional Root MAC Address : b88303-415600
IST Regional Root Priority : 0
IST Regional Root Path Cost : 0
IST Remaining Hops : 20

 

 

 

Site1-Router# sh span

Multiple Spanning Tree (MST) Information

STP Enabled : Yes
Force Version : MSTP-operation
IST Mapped VLANs : 1-4094
Switch MAC Address : 3cd92b-d9af80
Switch Priority : 32768
Max Age : 20
Max Hops : 20
Forward Delay : 15

Topology Change Count : 8
Time Since Last Change : 46 hours

CST Root MAC Address : b88303-415600
CST Root Priority : 0
CST Root Path Cost : 20000
CST Root Port : 24

IST Regional Root MAC Address : 3cd92b-d9af80
IST Regional Root Priority : 32768
IST Regional Root Path Cost : 0
IST Remaining Hops : 20

 

Does this mean each network is on its own spanning tree?  The Site1-Router shows the Core router as its root for 

CST Root MAC Address : b88303-415600.