Layer 2

DHCP snooping demystified

When reading about DHCP snooping at CCNA or CCNP level, its not very hard to get. On an access layer switch, we dont trust any port by default, and only trusted ports permit DHCP server messages. Thats not a big deal and not what this post is going to be about. But what happens in other scenarios?

There are many different scenarios when DHCP snooping can provide troublesome behavior if you don’t know what really happens under the hood of our switch functions.

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Interarea routing and path selection with OSPF

What path does OSPF choose to a specific destination?

Recently when I have been labbing OSPF more than before I noticed I stumbled when verifying the path ospf chooses for a specific destination. Lets look for instance at the topology here. First lets see with ospf database commands which path the routers uses and why, then how we can manipulate this.

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Protected Ports

Port protection is similar to private vlan, but much simpler. It is easier to configure “switchport protected” but it is only protected locally on the switch.

A protected port cannot communicate with any other protected port, but out all other ports on the switch. Therefore a protected port on SwA can communicate with a protected port on SwB, but neither can commnicate with any protected port on the same switch.

Simple as that. A private-vlan-light.

STP port-priority

Just started labbing for the CCIE R&S, had to think a bit at the part with STP port-priority to influence STP path. So i wrote some study notes which i will store here.

This first post will be about STP port-priority…

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