What is best practice for using UDLD?

[Alexey Yuskovich]

What is best practice for using UDLD?

[ZubairS]

UDLD is a Cisco-proprietary protocol. Switches from 3Com and its Enterprise division H3C have a similar feature called Device Link Detection Protocol (DLDP)

[Gerhard Roets]

Hi Alexey

I am assuming it is for an HP switch. I do not have any best practices I can think of quickly but I can offer you a few hints and tips :).

Good news is link-keepalive is not a very complex beast. Some recommendations

1. Read the chapter in the manual that covers it. Best place to start. Look at the release notes if there is any fixes that might be applicable before you implement it.

2. Use it only on ports between the devices that can experience a unidirectional links(fibre, ethernet wan both fibre and copper) since the link-keepalive frames verifies the path between two ports has bi-directional connectivity for the specific vlan it is enabled in.

3. Deploy it from the outside in so you can be sure you do not accidentally disable the link your are trying to cross as you enable it.

4. Remember if you have separate paths through an ethernet cloud between two switches that link-keepalive will verify. It will only verify the path for the specific vlan it is enabled on. So if that path fails for the vlan you are using link-keepalive in it will bring the whole port into failure state.

5. Regarding the timer. Link-keepalive was built as an addonn/helper for Spanning Tree. It is typically used if you have redundant inter switch links. The timer should only need to fire before the spanning tree bpdu is declared aged out.
The default of 5 seconds is a good place to start.
Just keep in mind it will take 4x5seconds(default) to detect and bring the link to failure state(uni-directional). If you need it to react faster you might need to review those settings. I would suggest not making that timer to aggressive as the frame does take some wire-space ;).

6. Remember the timer is set in deciseconds which is 0,1sec and not seconds :).

HTH
Gerhard