OSPF AREA 0

OSPF Area 0 Concept

OSPF designed with special restrictions when multiple areas are involved. If more than one area is configured in network, one of these areas has be to be area 0. This is called the backbone area. When designing networks it is best practice to start with area 0 and then extend into other areas as you move on.
The backbone area has to be at the center of all other areas, The requirement is all areas have to be physically connected to the backbone. The reasoning behind this is that OSPF expects all areas to inject routing information into the backbone area and in return the backbone will spread that information into other areas. The following diagram will provide more understanding about the flow of information in an OSPF network:

In the above diagram, all areas are directly connected to the backbone. In the rare situations where a new area is introduced that cannot have a direct physical access to the backbone, a virtual link will have to be configured.

Virtual links will be discussed later on. Different types of routing information which are coming from different types of areas. Routes that are generated from within an area are called intra-area routes. These routes are represented by the letter O in the IP routing table.

Routes that originate from other areas are called inter-area. The notation for these routes is O IA in the IP routing table.

Routes that originate from other routing protocols when redistribution happens and that are injected into OSPF called external routes. These routes are represented by O E2 or O E1 in the IP routing table.

 Multiple routes to the same destination are preferred in the following order: intra-area, inter-area, external E1, external E2.

Ref : Cisco.com

RATE Limit on Switches

Configure Rate-Limit on Cisco Switches

In the Cisco IOS on a Catalyst switch, there’s an Interface Mode command called shape round-robin queue bandwidth.specifically, the command is srr-queue bandwidth.

This command has been around since IOS 12.2(25). For these examples, Here is example of  Cisco Catalyst 3560 switch.

Entering the command appended with a question mark will display the command options. Here’s an example:

Switch(config)# interface f0/1

Switch(config-if)# srr-queue bandwidth ?

  limit              Configure bandwidth-limit for this interface

  shape             Configure shaping on transmit queues

  share              Configure shared bandwidth

As you can see, the command options are limit, shape, and share. While we’ll focus on the limit option this time, keep in mind that you can also use the srr-queue bandwidth command to shape and share bandwidth.

For example, as you have a 100-Mb Ethernet port on a Catalyst switch. You are selling or leasing bandwidth on that port, and a customer has bought 45 Mb of bandwidth. Then, you want to limit the outbound bandwidth on the port to 45 Mb instead of the full 100 Mb.

To do so, go to Interface Configuration Mode on the switch port, and apply the srr-queue bandwidth limit command. Here’s an example:

Cisco(config)# interface FastEthernet 0/1

Cisco(config-if)# srr-queue bandwidth limit 55

The 55 sets the outbound bandwidth limit on the port to 55 percent of the port speed. Since this is a 100-Mb port, this should limit the outbound traffic from the port to 45 Mb.

 

Other Options of bandwidth limiting

There are multiple ways to do this thing. One way would be to manipulate the port speed. But if you want to hard-code the port speed on the Ethernet port, Then you can do it in as mentioned in diagram: