adding new switches to layer2 network

[dfbnws]

Hi

i have to add two switches to l2 network (red highlighted ones) and want to know if there is any risk of a loop ?

[Reza Sharifi · Accepted solution]

Hi,

If the none red highlighted ones are layer-3, you should be fine. If they are layer-2, make sure to use the same type of STP protocol as the rest and know where the root and backup root switches are.

HTH

[dfbnws]

Thanks. All switches in the pic are in l2. 
the l3 gateway is further upstream in DC. the root bridges are also upstream. 
all the switches in the diagram have rstp running with 61440. 

[Reza Sharifi]

Your STP topology is getting larger as you add more L2-switches. If you have access to all these switches, you may want to consider making the middle tier 9ks the root and backup root. If you do want to go that route, it requires some planning, and changes should be done during a maintenance window.

HTH

[dfbnws]

thanks. agreed on the large l2 domain. but i cant make the middle ones root as the root is one level above those.

[Reza Sharifi]

The ones above them are fine too. It just that usually you want the root to be more centered but that works too. 

Good Luck!

[balaji.bandi]

Why you not considering vPC here, that makes Loops free and best utlise all the Links, that is the main reason nexus best advantage in DC environment, if not one of the side Block due to spanning tree that means one of the paths totally use less. (cost-wise not good ?)

what is the challenges here not to make vPC?

Another question, if they are in the same location, why you want to build and connect 4 tier, why not connect RED Switch 2nd Tier  - until you have again limitation please explain.

[dfbnws]

Cant connect directly to one level up due to port limitation. 
vpc wasnt originally confgured on the switches to which i am connecting now, and this is a temp solution till the port limitation issue is resolved. 
so spanning-tree will block alternate paths on my new switches, is there any risk of reconvergence and packet drops?

[balaji.bandi]

As long this does not become the root bridge set higher priority than others you ok.  just keep eye on STP is evil.

if the above Layer switch -  STP lower than 61440 you good.

Hope you are using Rapid PVST - is a good and fast conergence.