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Showing posts from March, 2013

BPDU Filter vs BPDU Guard

        Today we will try to explore the difference between these 2 options, BPDU guard and BPDU filter We know that BPDU are used to communicate between switches in L2 networks  to ensure loop free topology. BPDU Guard is used to protect our access (or trunks incase of servers) ports from receiving undesired BPDU packets, this feature is helpful in enforcing your network boundary in access layer BPDU Guard can be enabled on global configuration as well as under the interface configuration BPDU Filter on the other hand is used to filter BPDU packets outbound when configured  in global configuration (after sending 11 BPDU out ) and will filter BPDU inbound/outbound when configured under the interface level To better understand these two features, let’s use this simple topology R1 is connected to SW1 through F0/0 to have R1 send and receive BPDU we will simple configure bridging group 1 on the router and we will join the bridge group when desired to test our configuration BPDU

DTP Dynamic Trunking Protocol

The DTP is used by Cisco switches to negotiate if links  between two switches should be placed into access or trunk mode. .   The DTP also helps what trunking protocol (802.1Q or ISL) should be used. The individual DTP modes are:   dynamic auto - the port will negotiate the mode automatically, however, it prefers to be an access port dynamic desirable - the port will negotiate the mode automatically, however, it prefers to be a trunk port   Note: when you manually configure the trunk mode to be on using this command switchport mode trunk DTP will be still be sent of out of that interface. The following combinations will give you the results below dynamic auto + dynamic auto = access dynamic auto + dynamic desirable = trunk dynamic desirable + dynamic desirable = trunk dynamic auto + trunk = trunk dynamic desirable + trunk = trunk dynamic auto + access = access dynamic desirable + access =  access when you set the interface to static access, you are effectively disabling DTP on tha