Cisco CCNP / BSCI Certification Exam: Five OSPF Details You Must Know

Preparing for your BSCI exam on your way to the Cisco CCNP certification, you can quickly get overwhelmed by the details! Here are five commonly overlooked points you should keep in mind when it comes to your OSPF studies.

The virtual link command includes the area number of the transit area, and if authentication is being used on Area 0, the virtual link command must include the authentication statement. Since the virtual link is a logical extension of Area 0, it stands to reason that it has to be configured with the authentication type and password configured on Area 0.

OSPF requires no seed metric when routes are being redistributed into an OSPF domain. The default cost for such routes is 20, but you do need to use the "subnets" option if you want to redistribute subnets into OSPF.

There are two kinds of external OSPF routes. The default, E2, reflects the cost of the path from the ASBR to the external destination. The other option, E1, has a cost reflecting the entire path from the local router to the external destination.

When configuring stub areas, each router in the area must agree that the area is stub. For a total stub area, only the ABR needs to be configured with the "no-summary" option, but all routers in the area still must agree that the area is stub.

Routers in a stub area will have a default route to use to reach external destinations; routers in total stub areas will have a default route to use in order to reach both external and inter-area networks.

The BSCI exam and CCNP certification require a great deal of dedication and hard work. Keep studying and paying attention to the details, and you will get there!

Cisco CCNP / BCMSN Exam Tutorial: Changing Root Bridge Election Results

Your BCMSN and CCNP studies will include mastering the details of Spanning Tree Protocol (STP). While you learned some of these details in your CCNA studies, quite a bit of it may be new to you. Before going on to the intermediate and advanced STP features, let's review the root bridge election process and learn how to change these results.

Each switch will have a Bridge ID Priority value, more commonly referred to as a BID. This BID is a combination of a default priority value and the switch's MAC address, with the priority value listed first. For example, if a Cisco switch has the default priority value of 32,768 and a MAC address of 11-22-33-44-55-66, the BID would be 32768:11-22-33-44-55-66. Therefore, if the switch priority is left at the default, the MAC address is the deciding factor.

Switches are a lot like people - when they first arrive, they announce that they are the center of the universe! Unlike some people, the switches will soon get over it. BPDUs will be exchanged until one switch is elected Root Bridge, and it's the switch with the lowest BPDU that will end up being the Root Bridge.

If STP is left totally alone, a single switch is going to be the root bridge for every single VLAN in your network. Worse, that single switch is going to be selected because it has a lower MAC address than every other switch, which isn't exactly the criteria you want to use to select a single root bridge.

The time will definitely come when you want to determine a particular switch to be the root bridge for your VLANs, or when you will want to spread the root bridge workload. For instance, if you have 50 VLANs and five switches, you may want each switch to act as the root bridge for 10 VLANs each. You can make this happen with the spanning-tree vlan root command.

SW1(config)#spanning-tree vlan 1 ?

forward-time Set the forward delay for the spanning tree

hello-time Set the hello interval for the spanning tree

max-age Set the max age interval for the spanning tree

priority Set the bridge priority for the spanning tree

root Configure switch as root


In this example, we've got two switches, and SW1 has been elected the root bridge for VLANs 10, 20, and 30. We'll use the spanning-tree vlan root command on SW2 to make it the root bridge for VLANs 20 and 30.

SW2(config)#spanning-tree vlan 20 root primary

SW2(config)#spanning-tree vlan 30 root primary

SW2#show spanning vlan 20

VLAN0020

Spanning tree enabled protocol ieee

Root ID Priority 24596

Address 000f.90e2.1300

This bridge is the root

SW2#show spanning vlan 30

VLAN0030

Spanning tree enabled protocol ieee

Root ID Priority 24606

Address 000f.90e2.1300

This bridge is the root

SW 2 is now the root bridge for both VLAN 20 and 30. Notice that the priority value has changed from the default of 32768.

In the next CCNP / BCMSN tutorial, we'll take a look at more STP features.