WHAT IS A ROUTER?

A router is a networking device that forwards data packets between computer networks. Routers perform the traffic directing functions on the Internet. Data sent through the internet, such as a web page or email, is in the form of data packets

A router is a device that connects two or more packet-switched networks or subnetworks. It serves two primary functions: managing traffic between these networks by forwarding data packets to their intended IP addresses, and allowing multiple devices to use the same Internet connection.

There are several types of routers, but most routers pass data between LANs (Local AreaNetwork) and WANs wide area network. A LAN is a group of connected devices restricted to a specific geographic area. A LAN usually requires a single router.

A WAN, by contrast, is a large network spread out over a vast geographic area. Large organizations and companies that operate in multiple locations across the country, for instance, will need separate LANs for each location, which then connect to the other LANs to form a WAN. Because a WAN is distributed over a large area, it often necessitates multiple routers and switches*.

What are the different types of routers?

In order to connect a LAN to the Internet, a router first needs to communicate with a modem. There are two primary ways to do this:

• Wireless router: A wireless router uses an Ethernet cable to connect to a modem. It distributes data by converting packets from binary code into radio signals, then wirelessly broadcasts them using antennae. Wireless routers do not establish LANs; instead, they create WLANs (wireless local area networks), which connect multiple devices using wireless communication.
• Wired router: Like a wireless router, a wired router also uses an Ethernet cable to connect to a modem. It then uses separate cables to connect to one or more devices within the network, create a LAN, and link the devices within that network to the Internet.

In addition to wireless and wired routers for small LANs, there are many specialized types of routers that serve specific functions:

• Core router: Unlike the routers used within a home or small business LAN, a core router is used by large corporations and businesses that transmit a high volume of data packets within their network. Core routers operate at the “core” of a network and do not communicate with external networks.
• Edge router: While a core router exclusively manages data traffic within a large-scale network, an edge router communicates with both core routers and external networks. Edge routers live at the “edge” of a network and use the BGP (Border Gateway Protocol) to send and receive data from other LANs and WANs.
• Virtual router: A virtual router is a software application that performs the same function as a standard hardware router. It may use the Virtual Router Redundancy Protocol (VRRP) to establish primary and backup virtual routers, should one fail.

What is the difference between a router and a modem?

Although some Internet service providers (ISPs) may combine a router and a modem within a single device, they are not the same. Each plays a different but equally important role in connecting networks to each other and to the Internet.

A router forms networks and manages the flow of data within and between those networks, while a modem connects those networks to the Internet. Modems forge a connection to the Internet by converting signals from an ISP into a digital signal that can be interpreted by any connected device. A single device may plug into a modem in order to connect to the Internet; alternately, a router can help distribute this signal to multiple devices within an established network, allowing all of them to connect to the Internet simultaneously.

Think of it like this: If Bob has a router, but no modem, he will be able to create a LAN and send data between the devices on that network. However, he will not be able to connect that network to the Internet. Alice, on the other hand, has a modem, but no router. She will be able to connect a single device to the Internet (for example, her work laptop), but cannot distribute that Internet connection to multiple devices (say, her laptop and her smartphone). Carol, meanwhile, has a router and a modem. Using both devices, she can form a LAN with her desktop computer, tablet, and smartphone and connect them all to the Internet at the same time.

WHAT IS THE DIFFERENCE BETWEEN A ROUTER AND A SWITCH

While a network switch can connect multiple devices and networks to expand the LAN, a router will allow you to share a single IP address among multiple network devices. In simpler terms, the Ethernet switch creates networks and the router allows for connections between networks.

How does a router work?

Think of a router as an air traffic controller and data packets as aircraft headed to different airports (or networks). Just as each plane has a unique destination and follows a unique route, each packet needs to be guided to its destination as efficiently as possible. In the same way that an air traffic controller ensures that planes reach their destinations without getting lost or suffering a major disruption along the way, a router helps direct data packets to their destination IP address.

In order to direct packets effectively, a router uses an internal routing table — a list of paths to various network destinations. The router reads a packet’s header to determine where it is going, then consults the routing table to figure out the most efficient path to that destination. It then forwards the packet to the next network in the path.

To learn more about IP routing and the protocols that are used during this process,

WhatI Is Router Authentication Protocol

There are two general ways that authentication is implemented by most routing protocols: using a routing protocol centric solution that configures the passwords or keys to use within the routing protocol configuration, or by using a broader solution that utilizes separately configured keys that are able to be used by multiple routing protocols. Both OSPF and BGP use the prior of these methods and configure the specific authentication type and passwords/keys within their specific respective configurations. RIP and EIGRP utilize the former of these methods by utilizing a separate authentication key mechanism that is configured and then utilized for either RIP or EIGRP.

Keep in mind that these authentication solutions do not encrypt the information exchanged between the devices, but simply verifies that the identity of these devices.

Key Chains

The idea behind a key chain is rather simple as it simply replicates an electronic version of a key chain, a concept that most people are familiar with. The key chain functionality provides a mechanism for storing a number of different electronic keys, the key string value that is associated with a specific key and the lifetime that the key is valid. Any one of these configured keys can then be used by RIP or EIGRP for authentication.

Routing Protocol Authentication Configuration

As there are two different ways to configure routing protocol authentication; this article will review OSPF and BGP first as they require individualized configuration. The configuration of key chains and how they are used by RIP and EIGRP will then be covered.

OSPF Authentication

The configuration of OSPF requires a couple of different commands; which commands are used is determined by the type of authentication and method of authentication exchange. OSPF supports two different types of authentication that can be configured: authentication limited to a specific interface, or authentication configured over an entire OSPF area. Regardless of which of these options is selected there are also two different methods of authentication exchange that can be configured for each, these include: cleartext simple exchange, or MD5 exchange. When using MD5 the password/key that is configured is not sent between the exchanging devices, instead a hash is calculated and sent; this hash is then verified by the remote device to ensure identity.

The commands are required to setup OSPF interface (network) authentication is shown in Table 1.

Step 1	Enter privileged mode.	router>enable
Step 2	Enter global configuration mode.	router#configure terminal
Step 3	Enter interface configuration mode.	router(config)#interface interface-type interface-slot
Step 4	Configure OSPF (network) authentication.To configure MD5 authentication use the message-digest keyword.	router(config-if)#ip ospf authentication [message-digest]
Step 5	Configure the OSPF Authentication key.	router(config-if)#ip ospf authentication-key keyorrouter(config-if)#ip ospf message-digest-key key-id md5 key
Step 6	Exit configuration mode.	router(config-if)#end

The commands that are required to setup OSPF area authentication are shown in Table 2.

Step 1	Enter privileged mode.	router>enable
Step 2	Enter global configuration mode.	router#configure terminal
Step 3	Enter router configuration mode.	router(config)#router ospf process-id
Step 4	Configure OSPF area authentication.To configure MD5 authentication use the message-digest keyword.	router(config-router)#area area-id authentication [message-digest]
Step 5	Enter interface configuration mode.	router(config-router)#interface interface-type interface-slot
Step 6	Configure the OSPF Authentication key.	router(config-if)#ip ospf authentication-key keyorrouter(config-if)#ip ospf message-digest-key key-id md5 key
Step 7	Exit configuration mode.	router(config-line)#end

BGP Authentication

The configuration of authentication with BGP is very simple as it requires only a single configuration command. Unlike OSPF, BGP only supports the use of MD5 authentication.

The commands that are required to setup BGP authentication are shown in Table 3.

Step 1	Enter privileged mode.	router>enable
Step 2	Enter global configuration mode.	router#configure terminal
Step 3	Enter router configuration mode.	router(config)#router bgp autonomous-system
Step 4	Configure BGP authentication.	router(config-router)#neighbor {ip-address | peer-group-name} password key
Step 5	Exit configuration mode.	router(config-router)#end

RIP and EIGRP Authentication

As discussed above, the configuration of both RIP and EIGRP utilize key chains for their authentication configuration. This section will describe the process of setting up a key chain for use with RIP and EIGRP then cover the configuration of the specific authentication configuration required by each protocol.

Key Chain Configuration

The key chain configuration provides the ability to setup multiple keys that can be used by the supporting features. This includes the ability to have keys that potentially overlap in the time that they are valid. Keys can also be configured with specific transmit (send) and receive (accept) lifetimes that provide the ability to have keys automatically change at a predetermined time. The configuration required to setup a key chain are shown in Table 4.

Step 1	Enter privileged mode.	router>enable
Step 2	Enter global configuration mode.	router#configure terminal
Step 3	Create a key chain and enter key chain configuration mode.	router(config)#key chain name-of-key-chain
Step 4	Create a key and enter key configuration mode.	router(config-keychain)#key key-id
Step 5	Configure a secret key.	router(config-keychain-key)#key-string key-string
Step 6	Configure the receive key lifetime.	router(config-keychain-key)#accept-lifetime start-time {infinite | end-time | duration seconds}
Step 7	Configure the transmit key lifetime.	router(config-keychain-key)#send-lifetime start-time {infinite | end-time | duration seconds}
Step 8	Exit configuration mode.	router(config-keychain-key)#end

EIGRP Authentication Configuration

Once a key chain has been configured, the authentication for EIGRP neighbors is enabled on each interface that is connected to an authenticating neighbor. The configuration required to setup EIGRP authentication is shown in Table 5.

Step 1	Enter privileged mode.	router>enable
Step 2	Enter global configuration mode.	router#configure terminal
Step 3	Enter interface configuration mode.	router(config)#interface interface-type interface-slot
Step 4	Configure the use of a specific key chain key for authentication.	router(config-if)#ip authentication key-chain eigrp as-number key-chain-name
Step 5	Configure the use of EIGRP authentication.	router(config-if)#ip authentication mode eigrp as-number md5
Step 6	Exit configuration mode.	router(config-if)#end

RIP Authentication Configuration

As with EIGRP, once a key chain has configured the authentication, RIP authentication can be configured. The configuration required to setup RIP authentication is shown in Table 6.

Step 1	Enter privileged mode.	router>enable
Step 2	Enter global configuration mode.	router#configure terminal
Step 3	Enter interface configuration mode.	router(config)#interface interface-type interface-slot
Step 4	Configure the use of a specific key chain key for authentication.	router(config-if)#ip rip authentication key-chain key-chain-name
Step 5	Configure the use of RIP authentication.Unlike EIGRP, RIP supports a clear text authentication option using the text keyword, this mode is not recommended.	router(config-if)#ip rip authentication mode {text | md5}
Step 6	Exit configuration mode.	router(config-if)#end

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