Tuesday, 9 June 2015

Spanning-Tree BPDUs

Firstly introducing the newest member to the "Kylie's CCIE Lab" family. I found it really hard to find an affordable Layer 3 switch for my at home lab. Layer 3 switches seem to be a lot more expensive than routers. This 3560 cost me $90 plus $10 postage. I also got a second serial card for $55. This brings the total cost of my lab up to $430 so far. Things are getting serious.

Here's a photo of my new switch sitting on my routers. :)


I spent a bit of time today reviewing spanning tree protections.

BPDU Guard

Can be enabled globally or per interface (for portfast ports)
Puts a port into err-disable status if a BPDU is received on it

BPDU Filter

Drops BPDUs both inbound and outbound on an interface.
If enabled per interface, it can cause a switching loop because it will just silently and continually drop BPDUs both inbound and outbound. This is a way of terminating a STP domain.
Enabling it globally is safer. It is only enabled on portfast ports and will terminate when a BPDU is received. The port will go into STP negotiation.

Root Guard

Similar to BPDU Guard, except it only errdisables the port if the BPDU is declaring that it is coming from a superior root bridge.

LoopGuard & UDLD 

'nuff said :P

Something new... (for me)

How cool is the errdisable recovery feature. In production this could cause a lot of flapping on a port, but when testing BPDUguard it is great. Using "errdisable recovery interval 120", the interface comes back up every 2 minutes and errors again.


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