Ccna

This day, we’ll see how to think of summarizable address blocks in a slightly different way. And then we’ll see how this all applies to configuring route summarization with OSPF.

Please also read the previous article  OSPF — Part III

Thinking About How Big Blocks of Addresses Are

Let’s start by getting our bearings as far as size of address blocks. A Class C network address is a /24, with subnet mask 255.255.255.0. Let’s draw that as a “basic sized” rectangle, as shown in the figure.

Introduction

The OSPF routing protocol is playing an increasingly important role in modern networks. It is a multi-vendor standard. We’ll take a look at OSPF basics in this article.

Running OSPF so your routers can exchange information with NT servers is probably not a Good Thing. I personally don’t want servers sending routing information to my “official routing protocol”, since I’ve seen too many servers with duplicate IP addresses or other oddities. If a server administrator goofs and duplicates the server farm subnet on some workgroup server somewhere else, and it advertises it into your network, you’re in for a serious outage! If your group controls the servers, or if NT servers are acting as low-end routers at remote sites, well, then there’s a reason to run OSPF. I’ll just mention in passing here that OSPF has an authentication feature that allows you to easily exclude any “unofficial” routers from your OSPF Autonomous System (“group of consenting routers”).

Recall that an IGP is an Internal Gateway Protocol: whatever your routers speak “at home” — probably RIP, IGRP, EIGRP, or OSPF.

We saw that one of the usual reasons people have for wanting to run BGP is being multi-homed, either to one or two ISP’s. We examined the various “degrees of BGP” that you might wish to use, matching what you do to your needs and your skills. I hope that left you with the idea that there are some finer gradations in between “no BGP” and “full Internet routing with BGP”, sort of a 1-10 scale of increasingly difficult things to attempt.

Routing is used for the process of taking a packet from a device and sending it through a network to another device on a different network. If your network does not have a router, then obviously you are not doing routing.

To be able to do packet routing, there are things to know:
• Destination address
• The neighboring routers from which a router can learn about remote networks
• Possible routes to all remote networks
• The best route for any remote network

What is Network Address Translation?

The new Network Address Translation (NAT) functionality in the Cisco routers allows privately addressed networks to connect to public networks such as the Internet. When the privately addressed network (the “inside”) sends a packet through the NAT router, the addresses are converted to legal (registered) IP addresses before being passed to the “outside”.

Many sites have been using pass-through firewall gateways to provide this functionality. Well, it’s now available in your Cisco router!