Free CCNA Routing | Part 1 – Network Routing Review

Free CCNA Routing | Part 1 – Network Routing Review

Welcome to the Free CCNA Training Course. This series is for anyone who wants to build on their basic network skills, and even pass the CCNA 200-301 exam.

Section 2 of this series covers Layer-3/Routing. This covers topics like general routing, routing protocols, OSPF, and QoS (Quality of Service).

The website has additional links for further study to take you to the next level. Links are at the end of the description.

In this video, we’re going to cover:
0:00 Introduction
0:18 IP Addresses
7:16 Routers and Layer-3
14:41 The Routing Table

Layer-3 technologies focus heavily on IP addresses, and moving traffic from one network to another. In this section, we’ll focus on IPv4, and look at IPv6 in a coming section.

At layer-3, traffic is broken into packets, and sent from one host to another. If the hosts are on different networks, they need a router to help them by forwarding the packets on.

IP addresses are clever, as they contain both a network address and a host address. The subnet mask breaks the IP address into these two parts. This may be shown in Dotted Decimal Notation (DDN) or using Classless Interdomain Routing (CIDR). The subnet mask may change length, which is called VSLM (Variable Length Subnet Mask).

A host sends a packet to a router, by using the default gateway. The router knows more about the network, and is able to forward the packet to where it needs to go. This may include passing it through several routers.

The router is able to find the ‘direction’ to send the packet using the routing table. The routing table contains a list of all the networks that the router knows about, and how to get to them.

The routing table contains the destination network, the next-hop IP of the next router (if needed), and the interface the packet will be sent out on.

If a packet matches more than one route in the routing table, the most specific route will be chosen. This is called Longest Prefix Match (LPM).

Some switches can also act as routers. They’re called ‘Layer-3 Switches’, but can be thought of as routers in most cases.

Enable IP Routing on a switch (SDM):

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