Chapter 7

Question 1

A _______ is any piece of hardware or software that forwards packets based on their destination IP address. ______work, therefore, at the Network layer of the OSI model and at the Internet layer of the TCP/IP model.

Answer 1

router; Routers

Question 2

EXAM TIP:

A switch that works at more than one layer of the OSI model is called a ______ switch (MLS). An MLS that handles routing is often called a Layer 3 switch because it handles IP traffic.

Answer 2

multilayer

Question 3

Routing begins as packets come into the router for handling (Figure 7-5). The router immediately strips off any of the Layer _ information and drops the resulting IP packet into a _____(Figure 7-6). The important point to make here is that the router doesn’t care where the packet originated. Everything is dropped into the same queue based on the time it arrived.

Answer 3

2; queue

EXAMPLE:

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Question 4

The router inspects each packet’s destination IP address and then sends the IP packet out the correct port. To perform this inspection, every router comes with a _______ table that tells the router exactly where to send the packets. This table is the key to understanding and controlling the process of forwarding packets to their proper destination.

Answer 4

routing

SEE:

Figure 7-7 shows a very simple routing table for a typical home router. Each row in this routing table defines a single route. Each column identifies one of two specific criteria. Some columns define which packets are for the route and other columns define which port to send them out. (We’ll break these down shortly.)

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The router in this example has only two ports internally: one port that connects to an Internet service provider, labeled as WAN in the Interface column of the table, and another port that connects to the router’s built-in switch, labeled LAN in the table. Due to the small number of ports, this little router table has only four routes. Wait a minute: four routes and only two ports? No worries, there is not a one-to-one correlation of routes to ports, as you will soon see. Let’s inspect this routing table.

Question 5

__________ LAN IP A defined network ID. Every network ID directly connected to one of the router’s ports is always listed here.

Answer 5

Destination

NOTE:
The router uses the combination of the destination LAN IP and subnet mask to see if a packet matches that route. For example, if you had a packet with the destination 10.12.14.26 coming into the router, the router would check the network ID and subnet mask. It would quickly determine that the packet matches the first route shown in Figure 7-8.

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The other two columns in the routing table tell the router what to do with the packet:
Gateway & Interface

Question 6

To define a network ID, you need a subnet _____

Answer 6

Mask

NOTE:
The router uses the combination of the destination LAN IP and subnet mask to see if a packet matches that route. For example, if you had a packet with the destination 10.12.14.26 coming into the router, the router would check the network ID and subnet mask. It would quickly determine that the packet matches the first route shown in Figure 7-8.

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The other two columns in the routing table tell the router what to do with the packet:
Gateway & Interface

Question 7

The IP address for the next hop router; in other words, where the packet should go. If the outgoing packet is for a network ID that’s not directly connected to the router, the _______ column tells the router the IP address of a router to which to send this packet. That router then handles the packet, and your router is done. (Well-configured routers ensure a packet will get to where it needs to go.) If the network ID is directly connected to the router, then you don’t need a _______. If there is no ________needed, most routing tables put either 0.0.0.0 or On-link in this column.

Answer 7

Gateway; gateway; gateway

NOTE:

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Question 8

________ tells the router which of its ports to use. On this router, it uses the terms “LAN” and “WAN.” Other routing tables use the port’s IP address or some other description. Some routers, for example, use gig0/0 or Gig0/1, and so on.

Answer 8

Interface

NOTE:

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Question 9

A routing table looks like a table, so there’s an assumption that the router will start at the top of the table and march down until it finds the correct route. That’s not accurate. The router compares the destination IP address on a packet to _____ route listed in the routing table and only then sends the packet out. If a packet works for more than one route, the router will use the better route (we’ll discuss this more in a moment).

Answer 9

every

NOTE:

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Question 10

A properly configured router must have a ____for any packet it might encounter. Routing tables tell you a lot about the network connections. From just this single routing table, for example, the diagram in Figure 7-9 can be drawn.

Answer 10

route

PIC:

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Take another look at Figure 7-8. Notice the last route. How do I know the 76.30.4.1 port connects to another network? The third line of the routing table shows the default route for this router, and every router has one. (See the note below on the two exceptions to this rule.) This line says:

(Any destination address) (with any subnet mask) (forward it to 76.30.4.1) (using my WAN port)

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The default route is very important because this tells the router exactly what to do with every incoming packet unless another line in the routing table gives another route.

(Any packet for the 10.12.14.0) (/24 network ID) (don’t use a gateway) (just ARP on the LAN interface to get the MAC address and send it directly to the recipient)

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(Any packet for the 76.30.4.0) (/23 network ID) (don’t use a gateway) (just ARP on the WAN interface to get the MAC address and send it directly to the recipient)

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NOTE There are two places where you’ll find routers that do not have default routes: isolated (as in not on the Internet) internetworks, where every router knows about every single network, and the monstrous “Tier One” backbone, where you’ll find the routers that make the main connections of the Internet.

Question 11

NOTE:
Every modern operating system gives you tools to view a computer’s _______ table. Most techs use the command line or terminal window interface—often called simply terminal—because it’s fast. To see your routing table in Linux or in macOS, for example, type this command at a terminal:

Answer 11

routing

NOTE:
The netstat -r command works in Windows too, plus you can use route print as an alternative.

You should note two differences in the columns from what you saw in the previous routing table. First, the interface has an actual IP address—10.12.14.201, plus the loopback of 127.0.0.1—instead of the word “LAN.” Second—and this is part of the magic of routing—is something called the metric.

PIC:
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Question 12

A ______ is a relative value that defines the “cost” of using this route. The power of routing is that a packet can take more than one route to get to the same place. If a route were to suddenly cut off, then you would have an alternative. Figure 7-10 shows a networked router with two routes to the same place. The router has a route to Network B with a metric of 1 using Route 1, and a second route to Network B using Route 2 with a metric of 10.

Answer 12

metric

PIC:
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NOTE:
When a router has more than one route to the same network, it’s up to the person in charge of that router to assign a different metric for each route. With dynamic routing protocols (discussed in detail later in the chapter in “Dynamic Routing”), the routers determine the proper metric for each route.

NOTE:
Lowest routes always win. In this case, the router will always use the route with the metric of 1, unless that route suddenly stopped working. In that case, the router would automatically switch to the route with the 10 metric (Figure 7-11). This is the cornerstone of how the Internet works! The entire Internet is nothing more than a whole bunch of big, powerful routers connected to lots of other big, powerful routers. Connections go up and down all the time, and routers (with multiple routes) constantly talk to each other, detecting when a connection goes down and automatically switching to alternate routes.

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Question 13

I’ll go through this routing table one line at a time. Remember, every address is compared to every line in the routing table before it goes out, so it’s no big deal if the default route is at the beginning or the end.

The top line defines the default route:
(Any destination address) (with any subnet mask) (forward it to my default gateway) (using my NIC) (Metric of 25 to use this route). Anything that’s not local goes to the router and from there out to the _________ (with the help of other routers).

Answer 13

destination

PIC:

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PIC (Route print):

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Question 14

The next three lines tell your system how to handle the loopback address. The second line is straightforward, but examine the first and third lines carefully. Earlier you learned that only 127.0.0.1 is the __________, but according to the first route, any 127.0.0.0/8 address is the loopback. The third line is a little weird and is placed in the routing table to satisfy a loopback addressing requirement. Bottom line: no matter how you use a loopback address, as long as you start the address with 127, it will always go to 127.0.0.1.

Answer 14

loopback

PIC:

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PIC (Route print):

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Question 15

The next line defines the local connection:

(Any packet for the 10.12.14.0) (/24 network ID) (don’t use a gateway) (just ___ on the LAN interface to get the MAC address and send it directly to the recipient) (Cost of 1 to use this route).

Answer 15

ARP

PIC:

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PIC (Route print):

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Question 16

Okay, on to the next line. This one’s easy. Anything addressed to this machine should go right back to it through the loopback (127.0.0.1).

Answer 16

PIC:

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PIC (Route print):

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Question 17

The next line is for broadcasting to the other computers on the same network ID. In rare cases, you could have more than one network ID on the same network. This line targets only the nodes with the same _______ ID.

Answer 17

network

PIC:

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PIC (Route print):

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Question 18

The next two lines are for the multicast address range. Most operating systems put these lines in ____________.

Answer 18

automatically

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Question 19

The bottom lines define the default IP broadcast. If you send out an IP broadcast (255.255.255.255), your NIC knows to send it out to the _____ network. This will reach every node on the network, even nodes with varying network IDs.

Answer 19

local

PIC:

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PIC (Route print):

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Question 20

Exam Tip:

Frame Relay and ___ are ancient technologies that you won’t see in the real world. You’ll see them on the CompTIA Network+ exam, though.

Answer 20

ATM

Question 21

Most industry (that is, not home) routers enable you to add ______. You buy the router and then snap in different types of interfaces depending on your needs. Note the Cisco router in Figure 7-12. Like most Cisco routers, it comes with removable modules. If you’re connecting Ethernet to a DOCSIS (cable modem) network, you buy an Ethernet module and a DOCSIS module.

Answer 21

interfaces

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Question 22

Routers running some form of ________ _______ _________ (NAT) hide the IP addresses of computers on the LAN but still enable those computers to communicate with the broader Internet. NAT extended the useful life of IPv4 addressing on the Internet for many years.

Answer 22

Network Address Translation

EXAM TIP:
NAT replaces the source IP address of a computer with the source IP address from the outside router interface on outgoing packets. NAT is performed by NAT-capable routers.

Table 7-1 shows a sample of the translation table inside the PAT router. Note that more than one computer translation has been recorded.

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Question 23

The most common form of NAT that handles this one-to-many connection—called ____ Address Translation (PAT)—uses ____ numbers to map traffic from specific machines in the network.

Answer 23

Port; port

EXAMPLE:
John has a network at his office that uses the private IP addressing space of 192.168.1.0/24. All the computers in the private network connect to the Internet through a single router using PAT with the global IP address of 208.190.121.12/24. See Figure 7-14.

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** The obvious drawback to relying exclusively on PAT for network address translation is that it only works for outgoing communication, not incoming communication. For traffic originating outside the network to access an internal machine, such as a Web server hosted inside your network, you need to use other technologies.

Question 24

When an internal machine initiates a session with an external machine, such as a Web browser accessing a Web site, the source and destination IP addresses and port numbers for the TCP segment or UDP datagram are recorded in the NAT table, and the private IP address is swapped for the ______ IP address on each packet. Plus, the port number used by the internal computer for the session is also translated into a unique port number and the router records this as well. See Figure 7-15.

Answer 24

public

PIC:

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Table 7-1 shows a sample of the translation table inside the PAT router. Note that more than one computer translation has been recorded.

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Question 25

When the receiving system sends the packet back, it reverses the IP addresses and ports. The router compares the incoming destination port and source IP address to the entry in the ____ translation table to determine which IP address to put back on the packet. It then sends the packet to the correct computer on the network.

Answer 25

NAT

This mapping of internal IP address and port number to a translated IP address and port number enables perfect tracking of packets out and in. PAT can handle many internal computers with a single public IP address because the TCP/IP port number space is big, as you’ll recall from previous chapters, with values ranging from 1 to 65535. Some of those port numbers are used for common protocols, but many tens of thousands are available for PAT to work its magic.

Question 26

______ NAT (SNAT) maps a single routable (that is, not private) IP address to a single machine, enabling you to access that machine from outside the network. The NAT keeps track of the IP address or addresses and applies them permanently on a one-to-one basis with computers on the network.

Answer 26

Static

Question 27

With ___ forwarding, you can designate a specific local address for various network services. Computers outside the network can request a service using the public IP address of the router and the port number of the desired service. The port-forwarding router would examine the packet, look at the list of services mapped to local addresses, and then send that packet along to the proper recipient.

You can use port forwarding to hide a service hosted inside your network by changing the default port number for that service. To hide an internal Web server, for example, you could change the request port number to something other than port 80, the default for HTTP traffic. The router in Figure 7-16, for example, is configured to forward all port 8080 packets to the internal Web server at port 80.

Answer 27

port

PIC:

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Question 28

To access that _______ Web site from outside your local network, you would have to change the URL in the Web browser by specifying the port request number. Figure 7-17 shows a browser that has :8080 appended to the URL, which tells the browser to make the HTTP request to port 8080 rather than port 80.

Answer 28

internal

PIC:

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NOTE Most browsers require you to write out the full URL, including HTTP://, when using a nondefault port number.

Question 29

With dynamic NAT (DNAT), many computers can share a pool of routable IP addresses that number fewer than the computers. The NAT might have 10 routable IP addresses, for example, to serve 40 computers on the LAN. LAN traffic uses the internal, private IP addresses. When a computer requests information beyond the network, the NAT doles out a routable IP address from its pool for that communication. Dynamic NAT is also called _______ NAT. This works well enough—unless you’re the unlucky 11th person to try to access the Internet from behind the company NAT—but has the obvious limitation of still needing many true, expensive, routable IP addresses.

Answer 29

pooled

Question 30

A __ is defined as each time a packet goes through a router.

Answer 30

hop

EXAMPLE:

Let’s talk about hops for a moment. Figure 7-21 shows a series of routers. If you’re on a computer in Network ID X and you ping a computer in Network ID Y, you go one hop. If you ping a computer in Network ID Z, you go two hops.

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NOTE:
The hop count is a fundamental metric value for the number of routers a packet will pass through on the way to its destination network. For example, if router A needs to go through three intermediate routers to reach a network connected to router C, the hop count is 4. The hop occurs when the packet is handed off to each subsequent router.

Question 31

EXAM TIP:

CompTIA Network+ competencies break these many types of routing protocols into three distinct groups: _______ vector, ___ state, and hybrid. CompTIA obsesses over these different types of routing protocols.

Answer 31

distance; link

Question 32

A ______ is a relative value that routers use when they have more than one route to get to another network. Unlike the gateway routers in our homes, a more serious router will often have multiple connections to get to a particular network. This is the beauty of routers combined with dynamic protocols. If a router suddenly loses a connection, it has alternative routes to the same network. It’s the role of the ______ setting for the router to decide which route to use.

Answer 32

metric; metric

NOTE:
If a routing table has two or more valid routes for a particular IP address destination, it always chooses the route with the lowest metric. There is no single rule to set the metric value in a routing table. The various types of dynamic protocols use different criteria.

Question 33

Here are the most common criteria for determining a metric:

Hope Count
Bandwidth
Delay
Cost

Answer 33

NOTE:

Hop count The hop count is a fundamental metric value for the number of routers a packet will pass through on the way to its destination network. For example, if router A needs to go through three intermediate routers to reach a network connected to router C, the hop count is 4. The hop occurs when the packet is handed off to each subsequent router.

Bandwidth Some connections handle more data than others. An old dial-up connection theoretically tops out at 64 Kbps. A cable modem easily handles many millions of bits per second.

Delay Say you have a race car that has a top speed of 200 miles per hour, but it takes 25 minutes to start the car. If you press the gas pedal, it takes 15 seconds to start accelerating. If the engine runs for more than 20 minutes, the car won’t go faster than 50 miles per hour. These issues prevent the car from doing what it should be able to do: go 200 miles per hour. Delay is like that. Hundreds of issues occur that slow down network connections between routers. These issues are known collectively as latency. A great example is a satellite connection. The distance between the satellite and the antenna causes a delay that has nothing to do with the speed of the connection.

Cost Some routing protocols use cost as a metric for the desirability of that particular route. A route through a low-bandwidth connection, for example, would have a higher cost value than a route through a high-bandwidth connection. A network administrator can also manually add cost to routes to change the route selection.

EXAM TIP:
The CompTIA Network+ objectives list MTU as a switching or routing metric, and it definitely falls into the former category. The maximum transmission unit (MTU) determines the largest frame a particular technology can handle. Ethernet uses 1500-byte frames. Other technologies use smaller or larger frames.

If an IP packet is too big for a particular technology, that packet is broken into pieces to fit into the network protocol in what is called fragmentation. Fragmentation is bad because it slows down the movement of IP packets. By setting the optimal MTU size before IP packets are sent, you avoid or at least reduce fragmentation.

Question 34

_______ vector routing protocols were the first to appear in the TCP/IP routing world. The cornerstone of all distance vector routing protocols is some form of total cost. The simplest total cost sums the hops (the hop count) between a router and a network, so if you had a router one hop away from a network, the cost for that route would be 1; if it were two hops away, the cost would be 2.

Answer 34

Distance

NOTE:

All network connections are not equal. A router might have two one-hop routes to a network—one using a fast connection and the other using a slow connection. Administrators set the metric of the routes in the routing table to reflect the speed. The slow single-hop route, for example, might be given the metric of 10 rather than the default of 1 to reflect the fact that it’s slow. The total cost for this one-hop route is 10, even though it’s only one hop. Don’t assume a one-hop route always has a cost of 1.

Distance vector routing protocols calculate the total cost to get to a particular network ID and compare that cost to the total cost of all the other routes to get to that same network ID. The router then chooses the route with the lowest cost.

For this to work, routers using a distance vector routing protocol transfer their entire routing table to other routers in the WAN. Each distance vector routing protocol has a maximum number of hops that a router will send its routing table to keep traffic down.

Question 35

Routers are in convergence (also called ____ state), meaning the updating of the routing tables for all the routers has completed. Assuming nothing changes in terms of connections, the routing tables will not change.

Answer 35

steady

Question 36

The granddaddy of all distance vector routing protocols is the _______ __________ Protocol (RIP). The first version of RIP—called RIPv1—dates from the 1980s, although its predecessors go back all the way to the beginnings of the Internet in the 1960s. RIP (either version) has a maximum hop count of 15, so your router will not talk to another router more than 15 routers away. This plagues RIP because a routing table request can literally loop all the way around back to the initial router.

Answer 36

Routing Information

NOTE:

RIPv1 sent out an update every 30 seconds. This also turned into a big problem because every router on the network would send its routing table at the same time, causing huge network overloads.

As if these issues weren’t bad enough, RIPv1 didn’t know how to use variable-length subnet masking (VLSM), where networks connected through the router use different subnet masks. Plus RIPv1 routers had no authentication, leaving them open to hackers sending false routing table information. RIP needed an update.

Question 37

Routing Information Protocol Version Two (RIPv2), adopted in 1994, is the _____ version of RIP. It works the same way as RIPv1, but fixes many of the problems. VLSM has been added, and authentication is built into the protocol.

Most routers still support RIPv2, but RIP’s many problems, especially the time to convergence for large WANs, makes it obsolete for all but small, private WANs that consist of a few routers. The growth of the Internet demanded a far more robust dynamic routing protocol. That doesn’t mean RIP rests in peace! RIP is both easy to use and simple for manufacturers to implement in their routers, so most routers, even home routers, have the ability to use RIP (Figure 7-28). If your network consists of only two, three, or four routers, RIP’s easy configuration often makes it worth putting up with slower convergence.

Answer 37

current

Question 38

An Autonomous ______ (AS) is one or more networks that are governed by a single dynamic routing protocol within that AS.

Answer 38

System

PIC:

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Autonomous Systems do not deliver data between each other using IP addresses, but rather use a special globally unique Autonomous System Number (ASN) assigned by IANA. Originally a 16-bit number, the current ASNs are 32 bits, displayed as two 16-bit numbers separated by a dot. So, 1.33457 would be a typical ASN. Just as you would assign an IP address to a router, you would configure the router to use or be the ASN assigned by IANA.

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NOTE:

Autonomous Systems communicate with each other using a protocol, called generically an Exterior Gateway Protocol (EGP). The network or networks within an AS communicate with protocols as well; these are called generically Interior Gateway Protocols (IGPs).

NOTE:

Let me repeat this to make sure you understand the difference between EGP and IGP. Neither EGP nor IGP is a dynamic routing protocol; rather these are terms used by the large Internet service providers to separate their interconnected routers using ASNs from other interconnected networks that are not part of this special group of companies. The easy way to keep these terms separate is to appreciate that although many protocols are used within Autonomous Systems, such as RIP, the Internet has settled on one protocol for communication between each AS: the Border Gateway Protocol (BGP). BGP is the glue of the Internet, connecting all of the Autonomous Systems. Other dynamic routing protocols such as RIP are, by definition, IGP. The current version of BGP is BGP-4

Question 39

Routers can use one of two distance vector routing protocols: RIPv1 or RIPv_. Plus there’s an option to use a path vector routing protocol, BGP.

Answer 39

2

Question 40

The Internet has settled on one protocol for communication between each AS: the ______ Gateway Protocol (BGP).

Answer 40

Border

NOTE:
BGP is the glue of the Internet, connecting all of the Autonomous Systems. Other dynamic routing protocols such as RIP are, by definition, IGP. The current version of BGP is BGP-4.

The CompTIA Network+ exam objectives list BGP as a hybrid routing protocol, but it’s more technically a path vector routing protocol. BGP doesn’t have the same type of routing table as you’ve seen so far. BGP routers advertise information passed to them from different Autonomous Systems’ edge routers—that’s what the AS-to-AS routers are called. BGP forwards these advertisements that include the ASN and other very non-IP items.

EXAM TIP:
The CompTIA Network+ objectives list BGP as a hybrid routing protocol. Read the question carefully and if BGP is your only answer as hybrid, take it.

BGP also knows how to handle a number of situations unique to the Internet. If a router advertises a new route that isn’t reliable, most BGP routers will ignore it. BGP also supports policies for limiting which and how other routers may access an ISP.

BGP implements and supports route aggregation, a way to simplify routing tables into manageable levels. Rather than trying to keep track of every other router on the Internet, the backbone routers track the location of routers that connect to subsets of locations.

Route aggregation is complicated, but an analogy should make its function clear. A computer in Prague in the Czech Republic sends a packet intended to go to a computer in Chicago, Illinois. When the packet hits one of the BGP routers, the router doesn’t have to know the precise location of the recipient. It knows the router for the United States and sends the packet there. The U.S. router knows the Illinois router, which knows the Chicago router, and so on.

Question 41

The limitations of RIP motivated the demand for a faster protocol that took up less bandwidth on a WAN. The basic idea was to come up with a dynamic routing protocol that was more efficient than routers that simply sent out their entire routing table at regular intervals. Why not instead simply announce and forward individual route changes as they appeared? That is the basic idea of a _____ state dynamic routing protocol. There are only two _____ state dynamic routing protocols: OSPF and IS-IS.

Answer 41

link; link

Question 42

Open _______ Path First (OSPF) is the most commonly used Interior Gateway Protocols (IGP) in the world. Most large enterprises use OSPF on their internal networks. Even an AS, while still using BGP on its edge routers, will use OSPF internally because OSPF was designed from the ground up to work within a single AS. OSPF converges dramatically faster and is much more efficient than RIP. Odds are good that if you are using dynamic routing protocols, you’re using OSPF.

Answer 42

Shortest

NOTE:

OSPF offers a number of improvements over RIP. When you first launch OSPF-capable routers, they send out Hello packets, looking for other OSPF routers (see Figure 7-31). After two adjacent routers form a neighborship through the Hello packets, they exchange information about routers and networks through link state advertisement (LSA) packets. LSAs are sourced by each router and are flooded from router to router through each OSPF area.

https://learning.oreilly.com/library/view/comptia-network-certification/9781260122398/fig07-31.jpg

Once all the routers communicate, they individually decide their own optimal routes, and convergence happens almost immediately. If a route goes down, OSPF routers quickly recompute a new route with stored LSAs.

OSPF’s metric is cost, which is a function of bandwidth. All possible ways to get to a destination network are computed based on cost, which is proportional to bandwidth, which is in turn proportional to the interface type (Gigabit Ethernet, 10-Gigabit Ethernet, and so on). The routers choose the lowest total cost route to a destination network.

In other words, a packet could go through more routers (hops) to get to a destination when OSPF is used instead of RIP. However, more hops doesn’t necessarily mean slower. If a packet goes through three hops where the routers are connected by fiber, for example, as opposed to a slow 56-Kbps link, the packet would get to its destination quicker. We make these decisions everyday as humans, too. I’d rather drive more miles on the highway to get somewhere quicker, than fewer miles on local streets where the speed limit is much lower. (Red lights and stop signs introduce driving latency as well!)

OSPF isn’t popular by accident. It scales to large networks quite well and is supported by all but the most basic routers. By the way, did I forget to mention that OSPF also supports authentication and that the shortest-path-first method, by definition, prevents loops?

Why would anyone use anything else? Well, OSPF had one problem that wasn’t repaired until fairly recently: support for something called IPv6

EXAM TIP:
OSPF corrects link failures and creates convergence almost immediately, making it the routing protocol of choice in most large enterprise networks. OSPF Version 2 is used for IPv4 networks, and OSPF Version 3 includes updates to support IPv6.

Question 43

If you want to use a link state dynamic routing protocol and you don’t want to use OSPF, your only other option is _________ System to ________ System (IS-IS). IS-IS is extremely similar to OSPF. It uses the concept of areas and send-only updates to routing tables. IS-IS was developed at roughly the same time as OSPF and had the one major advantage of working with IPv6 from the start. IS-IS is the de facto standard for ISPs. Make sure you know that IS-IS is a link state dynamic routing protocol.

Answer 43

Intermediate; Intermediate

Question 44

There is exactly one protocol that doesn’t really fit into either the distance vector or link state camp: Cisco’s proprietary _______ Interior Gateway Routing Protocol (EIGRP). Back in the days when RIP was dominant, there was a huge outcry for an improved RIP, but OSPF wasn’t yet out. Cisco, being the dominant router company in the world (a crown it still wears to this day), came out with the Interior Gateway Routing Protocol (IGRP), which was quickly replaced with EIGRP.

EIGRP has aspects of both distance vector and link state protocols, placing it uniquely into its own “hybrid” category. Cisco calls EIGRP an advanced distance vector protocol.

Answer 44

Enhanced

EXAM TIP:
The CompTIA Network+ objectives list EIGRP as a distance vector protocol, right along with RIP. Read questions carefully and if EIGRP is the only right answer as a distance vector protocol, take it.

Question 45

Wow, there sure are many routing protocols out there. It’s too bad they can’t talk to each other … or can they?

The routers cannot use different routing protocols to communicate with each other, but many routers can speak multiple routing protocols simultaneously. When a router takes routes it has learned by one method, say RIP or a statically set route, and announces those routes over another protocol such as OSPF, this is called route redistribution. This feature can come in handy when you have a mix of equipment and protocols in your network, such as occurs when you switch vendors or merge with another organization.

Answer 45

A router takes routes it has learned by one method, say RIP or a statically set route, and announces those routes over another protocol such as OSPF