Showing posts from September, 2012

VTP - Should we use it?

VLAN Trunking Protocol: most commands can be configured in PRIVILEGED, CONFIGURE or DATABASE mode

- Have in mind that there is no way to dis-configure the VTP DOMAIN NAME (by default its NULL). You have to delete flash:vlan.dat and erase the Startup config and reload the router

VTP messages source IP (the IP from which the VTP messages are sourced):
(config)#vtp interface Loopback 1 [only]<- It will not be propagated

Restrict FLOOD TRAFFIC to the TRUNK Interfaces - use VTP PRUNING>
There are 4 types of VTP Advertisments exchanged between the switches:
1. Summary Advertisments - every time VTP database changes (every 300 ms)
2. Subset Advertisments - sent right after SUMMARY, includes what exactly changed
3. Advertisments requested from clients - client requests info to update the VTP database, server responds
4. VTP Membership announcements - when PRUNING is enabled, they tell the neighbor WHAT VLANs they want (if the VLAN is not announced with this message, it is not on the trun…

Spanning Tree: Root Election and Path Tuning

The concept is rather simple - The Switches send these probes called the BPDUs (Bridge Protocol Data Units) to discover loops in the network. If the BPDU “returns” – there is a loop in the network!

BPDU = 4-bit-PRIORITY + MAC Address
Spanning tree is no game, so be extremely careful when tuning the Priorities, Costs and Port-Priorities in order to manually make the Switch set your desired path as preferred. Each problem and mis-configuration can easily cause a major critical situation, as most of the Layer2 Loop Problems cause your Switches to immediately increase the CPU usage drastically. For your own stress-free dreams be sure to test in the Pre-Production environment everything you need to change in your production network regarding the Spanning Tree. I´m not going to get into the explaining the Spanning Tree basics here, as I guess most of the CCIE candidates should be familiar with it. The focus of this post will be the pure control of the Root Bridge in your network, and the prefe…