Hi,

I worry about effect of forcing core switch to root switch in a live network.

1. how much time it may take for STP convergence

2. we use only 2 vlans (data and voice) and never thought of pruning

3. show proc cpu sorted output is attached

4. no jumbo frames are used and detected on any interface

5. no PBR in LAN

regards

Kaushik

1. What is serving your default gateway for the clients? switch or 3800?

2. 20 switches connecting into stacked core?

Pings between switch and router are what?

Pings between client and switch are what?

Pings between client and router are what?

1. Default gateway for the clients is core switch.

2. All 20 switches are connected to stacked core switches

pings stats

core switch to router, client to switch, client to router

90% <3 ms, 5% 4-10ms,5% 10ms to 100+ms

The slowness problem is present for long time and our audit has told us to rectify

regards

Kaushik Vadali

Your connection between your switches and core should be <1ms

I would try to change the STP root for all vlans.

How many hosts on this data vlan?

Also, check your MTU to be 1500.

Dear Ralph,

Your connection between your switches and core should be <1ms

---Its not! for 10% pings

I would try to change the STP root for all vlans.

--- How much time it may take for STP convergance. As down time of morethan 1 minute is not allowed without scheduling

How many hosts on this data vlan?

--- 1500 hosts in 8 hrs, 24x7 operations

Also, check your MTU to be 1500.

--- MTU is default 1500 on all devices

regards

Kaushik Vadali

1500 clients on 1 vlan?

Theres your problem!

Breakdown that broadcast domain to use /24's and not anything bigger.

Since you connect the access switches to the stacked core, you really dont have any STP blocked ports and cannot have a loop.

Changing the STP root is best practice in this case but should not have an impact on this problem. I think you may lose connection for 1-3 secs only.

But I think you have a bigger problem and that may be your vlan size.

Dear Ralph,

I agree that we are using more hosts per vlan but cannot use /24 mask as per organization policy. I can use max /22 mask and limit to 1024 hosts

All hosts are DHCP enabled and work on single process, client server based CRM application

I plan for scheduling of core switch to be the root bridge and update you on the outcome soon

One Question - Do intermitant high latency (15 to 150 ms)is the cause for network slowness? Some points to note on Client systems are

- They are not working on internet

- They run and access only single CRM application located on the remote side of WAN

- Accessing common file server located on LAN

regards

Kaushik Vadali

So this application sits on another subnet on the remote side of the wan? if so you may have to look into tweaking it to serve multiple subnets and not just this one subnet your using as your data vlan. or is it spanned onto the same vlan?

For ex. Keep in mind that when a pc sends out an arp request for this app server, the switch floods this arp request to the whole vlan. Every host (1500 of them) will hear it and have to process it.

Try this. Create an new test vlan and SVI. Put a test pc in this vlan and point the default gateway to this svi. Do some tests.

Can you send your 3750 and 3560 config without actual IPs?

Dear Ralph,

I will try and update soon

regards

Kaushik Vadali