Creating Class B and Class C Subnets CHAPTER 10
`
`PART Ill
`
`Let's say that you've been assigned a Class B network address of
`l80.10.0.0. To subnet this network, you will have to steal bits from
`the third octet. You have determined that you want to create six sub-
`nets. Figure 10.11 walks you through the process of creating the sub-
`nets and creating the new subnet mask.
`
`Basic Subnet Mask: 255.255,0.0
`Network Address: 180.10.0.0
`
`/\First Node Oclel
`
`3 bits are required to
`create 6 subnets
`
`’idd’tl1e's::i_rrie'.‘riumberei’.
`I irigiremrdeyr birsmc e
`ate thesubriet mask; 1 ‘
`
`__
`
`Add high»order bits to create
`new subnet mask,
`
`12B+64+B2=224
`
`New Subnet Mask: 255.255.2243
`
`The new subnet mask for the network would be 25 5.255 .224.0 (see
`Figure 10.12). To figure out the range of IP addresses in each of the
`six subnets, you use the lowest of the high—order hits that were added
`to determine the new subnet mask number for the third octet. This
`
`would be 32 (again, taken from Figure 10.12). So, the first address in
`the first subnet would be 180.10.32.1 (180.10.32.0 is reserved as the
`subnetwork address and so cannot be used as a node address). To
`come up with the starting IP address of the second subnet, add 32 to
`the third octet (64). The second subnet would start with 180.10.64.1.
`Table 10.5 shows the ranges for the six subnets created from this
`Class B network address.
`
`196
`
`

`
`PART Ill Routing LAN Protocols
`
`CHAPTER 10 TCP/IP Primer
`
`Subnet#
`
`1
`
`StartAddress
`
`180.10.32.1
`
`18010.64-.1
`
`180.10.96.1
`
`l80.10‘128.1
`
`180.10.160.1
`
`18D.10.l92.1
`
`End Address
`
`180.10.63.254
`
`180.10.95.254
`
`180.10.127.254
`
`180.l0.159.254
`
`180.10.191.254
`
`l80.10.223.254
`
`Because you took 3 bits to create your subnets, you are left with 13
`bits for nodes. So, 213-2: 8190. That’s 8190 IP addresses available per
`subnet.
`
`Class C Subneiting
`
`Class C subnetting is a little more problematic than Class A and B
`networks because you only have one octet to steal bits from to create
`your subnets. Class C networks are also small to begin with (only
`254 IP addresses are available), so creating more than just a few sub-
`nets will leave you with a very small number of node addresses avail-
`able in each subnet.
`
`Let’s walk through an example that allows us to examine the idiosyn-
`crasies of Class C subnetting. The network address is 200.10.44.0.
`One octet is available for node addresses (the fourth octet). This is
`also the octet that you must borrow bits from to create your subnets.
`You will divide the Class C network into two subnets. To create the
`
`two subnets you must borrow the first two lower order bits that have
`the decimal value of 1 and 2 (1+2—1=2 subnets). You then move to
`the other end of the decimal bit values and use the first 2 high—order
`bits (because you borrowed 2 bits for the subnets) to create the new
`subnet mask for the network. The two high—order bits are 128 and
`64. Add them together and you get 192. So the new subnet mask for
`the network is 255.255.255.192.
`
`Figure 10.12 summarizes the steps that were followed to create the
`new network subnet mask by borrowing the appropriate number of
`bits to create 2 subnets.
`
`197
`
`

`
`Creating Class B and Class C Subnets CHAPTEH10
`
`PART III
`
`Basic Subnet Mask: 255.255.2550
`Network Address: 200.10/$4.0
`
`Borrow2high—order
`
`bilslo create subnet
`mask.
`
`/ N°deOclet
`
`12B 64 32 16 B 4 2 1
`
`2 bits are requlred to
`create 6 subnets
`1 +2-1 =2 subnet:
`‘
`
`‘
`
`0 Add high—order bits to create
`new subnet mask.
`
`128 +64 = 192
`
`New Subnet Mask: 255.255.225.192
`
`Now you need to figure out the range of IP addresses that will be
`available in the two subnets. The lowest of the high—o1'der bits used
`to create the new subnet mask was 64, which becomes the incre-
`ment for the subnet ranges. So, using what you learned when creat-
`ing Class A and Class B subnets, you would assume that the start
`address of the first subnet would be 200.10.44.64. However, remem-
`ber that an address in the range must be reserved as the subnetwork
`address. Because you are working with only one octet, the first
`usable address in the range of IP addresses for the subnet must be
`reserved as the subnetwork address. So, 200.10.44.64 is reserved for
`the subnet address.
`
`That means that the beginning of the range of IP addresses in the
`first subnet that you can use for node addresses begins with
`200.10.44.65. And the next subnet, which begins With Z00.10.44.l28
`(you add the increment to itself to get the start of the next subnet
`range) also reserves the first address (200.l0.44.12 8) as the subnet—
`work address (it identifies the subnet as a separate entity on the
`whole network). So the second subnet range of addresses that can be
`used for nodes begins with 200.10.44.129.
`
`198
`
`

`
`PART In Routing l.AN Protocols
`
`CHAPTER 10 TCP/IP Primer
`
`Table 10.6 shows the ranges for the two Class C subnets and also
`shows addresses such as the subnetwork address that cannot be used
`
`for node addressing.
`
`Subnetwork
`Address
`
`Start Address
`
`End Address
`
`Broadcast
`Address
`
`200.10.44.64
`
`200.10.44.65
`
`200.1044-.126
`
`200.10.4-4.127
`
`200.10.44-.128
`
`200.10.44.129
`
`200.l0.44.190
`
`200.10.44.191
`
`The big problem with subnetting a Class C network is that you lost a
`lot of normally usable IP addresses. You lost 2 addresses in each sub-
`net, one for the subnctwork address, and one for the hroadcast
`address. You also lost all the addresses that come before
`
`200.10.44.64. That means you lose 200.10/14.1 through
`200.10.44.63. That’s quite a few addresses, especially when you don’t
`get that many addresses with a Class C anyway.
`
`Understanding Subset 0
`
`There is a way to “cheat” and use these lost addresses for your net-
`work nodes (in our case addresses 200.10.44.2 through 200.10.44.62-
`200.10.44.l is reserved for the S11l311CtW0l‘iC address and 200.10.44.63
`would be the broadcast address). These “lost” addresses are referred
`to as subnet O and normally cannot be used. However, you can con—
`figure your router to take advantage of me subnet 0 IP addresses:
`type the ip subnet-zero command at the config prompt and then
`press Enter (this is a global configuration command, so you don’t
`have to enter it for any particular router interface).
`
`Using subnet 0 means that only 1 bit needs to be stolen to create
`subnet 0 and subnet 1. So, the subnet mask would now be
`255.255.255.128 (only 1 high—order hit is used to create the new sub-
`net mask). The range of IP addresses for the two subnets would be
`200.10.44.1—200.10.44.126 (200.10.44.127 is the broadcast address)
`for subnet 0 and 20010.44.129-200.10/44.254 (200.10.44.128 is the
`subnetwork number and 200.10.4-4.255 is the broadcast address) for
`subnet 1.
`
`i
`
`Calculatm avallah
`nbdé alldvres
`V
`To duiekly calculate m
`if number of ll‘ addresse
`that would be availahl
`» each of our Classlisubinets ~_
`use the formula 2 [W5 = Av
`available for node
`.v
`,
`addlessesl minus 2. ln our
`case this would be 25 ~
`-.
`2:62. You have 2 subrréts
`so 62><2=l24.
`
`199
`
`

`
`
`
`;~;_,,.t...x;¢.—.
`
`:liI E7E
`
`Creating Class B and Class C Subnets CHAPTER 10
`
`PART Ill
`
`Because using subnet 0 makes the calculation of subnets a little more
`difficult (When compared to Class A or B), Table 10.7 provides a
`summary of the fourth octet numbers that would be available for
`each subnet when a Class C network is subnetted with subnet 0 used
`
`as a valid subnet. Values are provided for 2, 4, and 8 subnets on the
`Class C network.
`
`The big thing to remember when using subnet 0 is that you don’t
`subtract 1 from the low-order bits when you determine the number
`of hits you must steal to create the required number of subnets.
`
`Subnet Mask
`
`Start Address
`
`End Address
`
`255.255.255.128
`
`x.x.x.l
`
`x.x.x.129
`
`255.255.255.192
`
`x.x.x.126
`
`x.x.x,254
`
`X.x.X.62
`
`x.x.x.126
`
`x.x,x.19O
`
`x.X.x.254
`
`255.255.255.224
`
`x.x.x.1
`
`x.x.x.3 3
`
`x.x.x.65
`
`x.x.x.97
`
`x.x.x.129
`
`x.x.x.l6l
`
`x.x.x.193
`
`x.X.X.225
`
`x.x.x.31
`
`x.x.x.63
`
`x.x.x.95
`
`x.x.x. 127
`
`x.x.x.l59
`
`x.x.x.191
`
`x.x.x.223
`
`x.x.x.255
`
`200
`
`

`
`PART III Routing LAN Protocols
`
`CHAPTER 10 TCP/IP Primer
`
`% Fatal Word on gtlfianetttag
`
`On any network that uses internetworking connectivity strategies,
`you will most likely face the issue of dividing a particular IP network
`into a group of subnets. And understanding the simple math pre-
`sented in this chapter will make it very easy for you to create subnets
`on any class of network; however, sometimes it can be even simpler
`1
`to just look up the information on a chart.
`
`Table 10.8 provides a sunmiaiy of the subnet mask and the number
`of hosts available when you divide a Class A network into a particular
`number of subnets (subnet 0 has not been allowed). Table 10.9 pros
`vides the same information for Class B networks (subnet O has not
`been allowed).
`
`# Of Subnets
`
`Bits Used
`
`Suhnet Mask Hosts/Subnet
`
`2
`
`6
`
`14
`
`2 25S.192.0.0
`
`3 2S5.224.0.0
`
`4 255.240.0.0
`
`5 255.248.0.0
`
`6 255.252.0.0
`
`7 255.254-.0.0
`
`255.255.0.D
`
`4,194,302
`
`2,097,150
`
`1,048,574
`
`524,286
`
`262,142
`
`131,070
`
`65,534
`
`# Of Subnets
`
`Bils Used
`
`Subnet Mask
`
`Hosts/Subnet
`
`‘
`
`2
`
`6
`
`14
`
`30
`
`62
`
`255.255.1920
`
`255.255.2211-.0
`
`255.255.2400
`
`255.255.248.0
`
`255.255,252.0
`255255.254-.0
`
`16,382
`
`8,190
`
`4,094
`
`2,046
`
`1,022
`510
`
`
`
`255.255.2551) 254
`
`201
`
`

`
`Conf
`"
`UuHHUW.
`
`I P R0 uti ng
`
`Configuring Router interfaces
`
`Configuring a Routing Protocol
`
`Dynamic Routing Versus Staticfiouting
`
`Using Telnet
`
`202
`
`

`
`PART Hi Routing LAN Protocols
`
`CHAPTER H Configuring IP Routing
`
`fiantigttrittg heater tatertaees
`As you’ve already heard several times in this book, TCP/IP is the de
`facto network protocol for the networks of the world (due to the
`Internet exp1osion——everyone wants to be part of this planetwidc
`network). It is a routable and robust network protocol stack. You
`learned all about ll) addresses and II’ subnetting in Chapter 10,
`“TCP/ll? Primer.” Now, yo11 can take some of the concepts learned
`in that chapter and apply them directly to router configurations.
`Routing II’ on an internetwork requires that you complete two main
`tasks: configure LAN and WAN interfaces with the correct I]? and
`subnet mask information, and then enable an IP routing protocol on
`your router or routers. GP routing is automatically enabled on the
`router in contrast to IPX and AppleTalk, which aren’t.) VVhen rout~
`ing 11’, you have more than one choice for your routing protocol
`(such as RIP Versus IGRP).
`Let’s walk through the steps of configuring LAN interfaces on a
`router first and apply some of the information that you picked up on
`IP subnetting in Chapter 10. For example, assume your example net-
`work is a Class B network with the network address 130.10.0.0. You
`will create 6 subnets on this network. The new subn et mask for the
`network would be 255.25 5.2.24.0.
`
`Table 11.1 provides the range of IP addresses for the 6 subnets.
`
`Start Address
`
`130.10.32.1
`
`130.10.64.1
`
`130.‘10.96.1
`
`130.10.128.1
`
`130.10.160.1
`
`130.10.192.1
`
`End Address
`
`130.10.63.254
`
`130.10.95.254
`
`130.10.127.25‘!
`
`130.10.159.254
`
`130.10.191.254
`
`130.10.223.254
`
`
`
`-.~‘§‘3’\“’3“5<'7é‘il‘l‘iI-\i1~s1L'w)N/I‘*A‘v"t~fiw$ria$W~m».~2e:.,.,,;L~L"'IIV)'V!>V«v\;'q»>fi\\‘\b““<«;,¢fi;-«Ib1'V.‘|‘
`
`
`
`
`
`203
`
`

`
`Configuring Router Interfaces CHAPTER 11
`
`PART HE
`
`Figure 11.1 shows a diagram of a portion of a company internet-
`work. IP addresses (from our range in Table 11.1) have been assigned
`to the router interfaces on each of the routers. This figure will help
`provide some context to the IOS commands that you are going to
`work with in this chapter.
`
`Branch Office A
`
`Eirarich Office B
`
`IP Address
`intedace
`Elherncto 130.10.32.1
`Serial 0
`130,10.64,1
`Ethernet Seriali
`1ao.1o.12s.1
`
`iP Address
`Interface
`Eihernem 130.10.96.1
`Serial 0
`130.10.64.2
`Seriali
`130.10.160.1
`
`’ Serial 0
`
`Serial 0
`
`4500 Series
`Hauler
`
`Central Offices
`
`You will configure the 2505 router at the Branch A location. This
`means that the router (which has three interfaces, one Ethernet, and
`two serial) must have each interface configured with a different [P
`address that is in a different subnet range. Table 11.2 lists the IP
`addresses (also shown in Figure 11.1) that you will use to configure
`this router‘ You will learn about configuring LAN interfaces (such as
`Ethernet ports) in the next section, “LAN Interfaces” and WAN
`interfaces in the section after that, “WAN Interfaces.”
`
`204
`
`

`
`PART III Routing LAN Protocols
`
`CHAPTER 11 Conf1guxingIP Routing
`
`Interface
`
`Ethernet 0
`
`Serial 0
`
`Serial 1
`
`SEE ALSO
`
`IP Address
`
`l30.10.32.1
`
`13010.64-.1
`
`l30.10.128.I
`
`For an ouerzlim vfIP ro1m'11gpratawI.r.mc/J :7: RIP and IGRP, see page 93.
`
`LAN interfaces
`
`LAN interfaces, such as Ethernet ports or Token Ring ports, wi]
`the connection point between the router and a local area networ
`The number of subnets at 3
`her of LAN interfaces required on the router (if only one router
`used).
`Each of these LAN interfaces will he on a separate snhnet. The
`plest way to assign IP addresses to a LAN interface is to use the
`II’ address available in the address range of the subnet that the i
`face will connect to.
`
`Configuring IP addressing for a LAN interface
`1. At the Privileged prompt type config t, and then press Ent
`You are placed in the Global Configuration mode.
`. To configure a particular LAN interface, type the name 0
`interface at the prompt, such as interface etherne
`‘
`ress Enter. The rom t chan es to the config-if mode.
`P
`P
`P
`E
`»
`. Now you can enter the ip address command followed by the;
`address for the interface and the suhnet mas
`'
`this example, the command would be ip address 13o.1@ .3
`255.255 .224. 0 (see Figure 11.2). Press Enter to complete
`command.
`4. To end the configuration of the interface, press Ctrl+Z.
`5. Press Enter again to return to the privileged prompt.
`
`205
`
`

`
`Configuring Router Interfaces CHAPTER 1"’!
`
`PART Ill
`
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`tor nunfi In-utinn em-manrln. una per line.
`npoyn(unI|P g)Nint an
`ny.ya<cnnfig—J£)lIip addreas 1aB.1u.a2,x. 25: 255.22-Lia
`Lu1£y=(cImEig—if)fl
`
`1 You can quickly check the configuration parameters for a LAN port
`using the show ip interface command. For example, to see the IP
`addressing for Ethernet 0, you would type show ip interface em and
`then press Enter. Figure 11.3 shows the results of this command on
`our 25 O5 router.
`
`eyeflslwu in int all
`Internet nidrezxx is 3B.1E.32.i/19
`- liarnctfl is up,
`line rvlrncul is up
`Brnadcast addv-nun in 255.255.255.255
`fldllx-nus data:-ninnd by setup unnnzmd
`HIII
`‘ls isms bytes
`"ulnar address in not set
`Diracted ]u‘un|'1cast ram-u-ding is enabled
`Outgnins acuuuc list in not not
`Inbuunll
`accnuz list is nut set
`Proxy M11’ is cnnblcrl
`Baum-ity levnl is dnfiault
`Split lluriaon it enabled
`[GNP )\:IlirN:|:n 31-3 111-1391: want
`ICMP unrnachahlar: are always sent
`ICHP mask l'fl]I17lE: arn rumor sent
`[P Faust nuitclling is disahirl
`[P Past zmitlflliml an the same intn|~Fa::a it disabled
`H-‘ nultiuast fast suibuhilw is enabled
`flnutar Disc-Ivory in dluablnrl
`[P nuepu: yicket Accounting is disabled
`IP accent violation announcing‘ is disabled
`{GP/IF header cnnpressiuu 1:: disabled
`Pm):-a prnxy qmna replies are Ilinahlad
`Gateway luucnu-my 1: nil.-mblnd
`Policy rnutimz is xlinahlall
`Nutwflvli addxza: kranslatiun is disabled
`
`Ifyou look at the IP information provided in Figure 11.3, the IP
`address reads as 130.10.32.1/19, and no suhnet mask information is
`provided. You entered 130.] 0.32.1 as the IP address for the interface
`in the previous set of steps. So, What does the /19 mean? Actually,
`this is the router’s way of telling you the subnet mask.
`
`The 19 is the number of bits that are used for network addressing
`plus the number of bits used to create the subnets on this network.
`Normally, a Class B network uses two octets (16 bits) to define the
`network number for the network: in this case 19—16=3. This shows
`you the number of bits stolen for subnetting. If you take the first
`three high—order bits and add them (128+64+32), you get 224, which
`tells you that the subnet mask is 255.255 .224.0.
`
`er
`IP addressinnjbf all mg __
`interfaces on the‘router‘ ’
`V
`willbe displayedt
`E =
`
`I
`
`206
`
`

`
`5.: figuration
`saVed'tuiNVHl
`
`be builta
`.
`
`PART III Routing LAN Protocols
`
`CHAPTER 11 Cnnfiguiiing IP Routing
`
`VVhenever you see notation like the /19, just take that number and
`subtract the number of bits that are normally used for the class of
`network that you are working with. This always gives you the subnet
`bits, which can then be used to quickly calculate the subnet mask.
`
`WAN interfaces
`
`WAN interfaces can be configured with IP addresses exactly in the
`same way that you configure LAN interfaces. To configure a serial 0
`interface on a router, you would complete the following steps.
`
`Configuring IP addressing tor a serial interface
`
`1. At the Privileged prompt, type config t, and then press Enter.
`You are placed in the Global Configuration mode.
`
`. To configure a particular LAN interface, type the name of the
`interface at the prompt, such as interface serial 0. Then press
`Enter. The prompt changes to the config-if mode.
`
`. Now you can enter the IP address command followed by the II’
`address for the interface and the subnct mask for the network. In
`
`this example, the command would be ip address 13@.1@.64.1
`255.255 .224. 0 (see Figure 11.4). Press Enter to complete the
`command.
`
`upuyuikclznfjg :
`upauz(¢:uuf zflllinl: sfi
`End with ENTI./Z.
`ter configuration cuunamiz. mu: yer 1in=.
`up-:yu(cunl‘:ig if)Ili
`address.‘ 1ElB.1fl.6§.1 255.255.2211.!)
`(cmlfi
`EN!
`.
`
`4. Toiend the configuration of the interface, press Ctrl+Z.
`5. Press Enter again to return to the privileged prompt.
`
`You can use the’ show ip interface so command to check the config-
`uration of the serial interface.
`
`One issue relating to the number of IP addresses you have available
`to configure the routers, hosts, and servers on your network rears its
`ugly head when you are configuring WAN interfaces. An entire sub-
`net (an entire range of IP addresses) must be wasted to configure the
`serial interfaces on two routers that are connected by a particular
`
`connection.
`
`207
`
`

`
`Configuring a Routing Protocol CHAPTER 11
`
`PART III
`
`For example, in the case of our two 2505 routers in Figure 11.1, they
`are connected by their serial 0 interfaces (using a particular WAN
`connection and protocol). This connection must be configured as a
`separate subnet, meaning the serial 0 interface on the Branch Office
`A router will use one address in the chosen subnet range and the ser—
`ial 0 interface on the Branch Office B router will use one address
`
`from that same subnet range. So, you basically fritter away all the
`other addresses in that subnet range.
`
`To overcome this obvious waste of IP addresses, you can configure
`your serial interfaces without IP addresses (they will still route IP
`packets even though they are designated as IP mzm71l1ered). The com-
`mand used at the configuration prompt for the interface is ip unnum-
`bered [interface or virtual interface]. The interface or virtual
`interface parameter is the designation of an actual interface, such as
`Ethernet 0, or a Virtual interface such as loopback 0, that has been
`configured with an IP address (see Figure 11.5).
`
`npayallnunfiu t
`n ‘tar Iznnl’l§\n'atinn Imnnamln, unu her line.
`a1zeva(::nnf1g>iIine .-:1
`nimyntonnfirinlin unnunhm-er! ctllcrnut ul
`
`Em! with min/z.
`
`If you use if) unnumbered on a serial interface, the serial interface that
`it connects to via a WAN connection must also be configured as IP
`unnumbered. The drawbacks of configuring a serial interface as IP
`unnumbered, is that you cannot Telnet to that serial interface or ping
`that interface (because it doesn’t have its own IP address). Also, if the
`interface to which you “hooked” the serial port, such as Ethernet 0
`(shown in Figure 11.5) goes down, you might not be able to reach
`the connection that the serial interface is attached to.
`
`Configuring 3 Routing Protocol
`
`After you have the interfaces on the router configured with the
`appropriate IP addresses and subnet mask, you can configure a rout-
`ing protocol. Different lnterior Routing Protocols (protocols used
`for routing on your internal internetwork) are available and your
`choice of a routing protocol will depend on the size of your internet—
`work. For example, RIP is fine for small internetworks but is limited
`
`208
`
`

`
`m an éhme
`the c5nfig’u’,afi0n
`
`ou_.Ca
`’
`
`'
`
`'
`'
`
`"
`
`PART III Hauling LAN Protocols
`
`CHARTTER11 Configuring |PRou1ing
`
`to 15 hops (from router to router), making its use on large internet—
`works a problem. For larger internetworks you may want to use
`IGRP or OSPF. You will look at the configuration of RIP and the
`configuration of IGRP in the next two sections of this chapter.
`SEE ALSO
`
`For an overview rfll’ rat/ri11gp1'omcnlr rm}; (1: RIP mm’ ICRR tee page pg.
`
`Configuring REP
`
`RIP is a distance—vector routing protocol that uses hop count as its
`metric. RIP summarizes the information in the routing table by IP
`network numbers (also referred to as major network numbers).
`
`Configuring RIP is very straightforward. You must first select RIP as
`your routing protocol and then let RIP know the major network
`number for each interface you have enabled for IP routing. In the
`sample network that you have been discussing (see Figure 11.1), you
`are working with only one major network number, 130.10.0.0. So,
`you only need to specify this network when configuring RIP on our
`router.
`
`Configuring RIP
`
`1. At the privileged prompt, type config t, and then press Enter.
`You are placed in the Global Configuration mode.
`
`. At the config prompt, type router rip, and then press Enter.
`This selects RH’ as the routing protocol.
`
`. Type network [major network number] at the Config prompt. The
`major network number is the network address for a class A, B, or
`C network that is directly connected to the router. In your case,
`you are connected to one major network 130.10.0.0. ' ‘herefore,
`the command would be network 130.10.0 . 0 (see Figure 11.6).
`Press Enter to continue.
`
`. Repeat the network [major network number] for each IP network
`that the router is directly connected to. For example, if different
`Class C networks are connected to several Ethernet interfaces,
`
`you must repeat the network command for each of the network
`addresses for these Class C networks.
`
`209
`
`

`
`Configuring a Routing Protocol CHAPTER 11
`
`PART III
`
`nte-L‘ configuration commands, nnn per line.
`npey:-.<cunng)n:-uutm- rip
`urn-)IIueo;uu:-k 13Ia.1B.B.B
`
`End um. CHTL/Z.
`
`. When you have finished entering the directly connected net-
`works, press Ctrl+Z to end the configuration session.
`
`6. Press Enter to return to the Privileged prompt.
`
`After you’ve configured RIP on your router, you can use the IOS
`commands that provide a view of RIP routing information such as
`the routing table and the settings for RIP broadcasts.
`
`To View the RIP routing table, type show ip route at the user or
`privileged prompt and then press Enter. Figure 11.7 shows the
`results of this command on a 2505 router that is connected to
`another 2505 router via a serial connection. Subnets that are directly
`connected to the router are marked with a C (interfaces that were
`configured on that router). Other subnets that are reached by a par-
`ticular directly connected subnet are marked with an R (these net-
`work locations are learned by RIP).
`
`117 rnute
`npeya
`nubile, II - IMP
`I - IGRP. Tl - RU‘. H
`urlns: C - ennnected, S — static,
`1) — Emnr. Ex — mnnr external, 0 — 05911, In — DSFF inI:I:r area
`E1 — OSPP external tyne 1. El —- as»? external type 2, E — GP
`ML - OSPF NSSII external type 1, NZ - 081'? NSSFI uxtevnal byfio 2
`:1 ~ 1545. L1 ~ I3-ls level-1, 1.2 — [S-IS 1aUn1~2,
`-x- — nnduatu default
`U - pea‘-uaur static rulktn. u — ODJ1
`azmmy of last x-emu-I: is not use
`13e.m.u.ta/1v is subnerzzd, 3 sulmate
`135.10.32.53 in directly cnnnncl.‘-ad, Etlu-n-new
`138.1l5.fi1.B is directly cnnnzcted, Sex-inlfl
`1au.1u.9t.a [12E/1] via 13fl.1Fi.fi4_2, Im:aa:19, Sarialli
`
`npayell
`
`You can use the show ip protocol command to View the timing
`information related to RIP. For example, RIP updates are sent eveiy
`30 seconds. The hold—down time for RIP is 180 seconds. This means
`that if a router doesn’t receive :1 RIP update from a connected
`router, it waits 180 seconds from the last received update and then
`flags the subnet path as suspect. After 240 seconds, the router will
`actually remove the path information related to the other router
`from the routing table because it considers the path no longer
`usable.
`
`210
`
`

`
`PART III Houling LAN Protocols
`
`CHAPTER 11 Configuring IP Routing
`
`Type show ip protocol at the user or privileged prompt and then
`press Enter. Figure 11.8 shows the results of this colnzuarid.
`
`npayauah ip pl-ntm:I7J.
`nuting Protocol is "rip"
`Invalid a car 13!] saimmlu. hold down 183. flu-zlicd after 248
`Sending update: em-y an nenullilx. ma: due in 2 seconds
`Outgnim; upnlalu filtum link fnr all inturfacas iv: not set
`Incnmin
`umlutn filter list For all inter-facas is not set
`flenlislrr utingt rip
`_
`Default Uersinn cnntx-cl: snnd var.-axon 1,_ receive any uex-sinn
`Inbnrfacs
`Send
`liacu
`Kuy—i:l1a).n
`Etlievnew
`J.
`1 2
`Saxiialfl
`1
`1 2
`Saxliali
`1
`1 Z
`1\.nul:in
`for Nntum-kc:
`13B. E.fl.fl
`Routing Infurnntinn Emu-nun:
`Gateway
`Distance
`13H.1B.64..2
`128
`llistanne: (default u 12m)
`npayall
`
`Last Update
`uflcflfiififl
`
`If you want to View RIP update messages as they are sent and
`received by 21 router, you can use the debug ip rip command. Type
`debug ip rip at the privileged prompt and then press Enter. Figure
`11.9 shows the results of this command.
`
`yufldahus 1;; Vin
`I:
`m'ato|:nl dzflillqsillg in MI
`RIP: nacuiuad U1 update E1-an 13fl.1fl.fi-1.2 rm Sm-lnllfl
`13B.ifl.96.B in 1 Imps
`RIP: sending U1 update tn 255.255.255.255 via Etliax-natfl C1ElB.1B.32.1)
`nuhnat 13fl.1fl.fi‘i.B. matric 1
`aulrmst 13fl.1fl.96.Ei. netri-: 2
`RIP: sending 01 u date (in 255.255.255.255 via Serialfl 0.33.13.54.13
`uulznnk 198. 8.32.5, nut:-in 1
`INF: runaiuad 01 update from 13D.1fl.EIL2 flll Serialfl
`'13U.1H.96.B in 1 hops
`NIP: sanding 01 1| olnte tn 255.255.255.255 via Etharnntfl (13E|.1B.32.1)
`aulmet: 13B. fl.61.B. Metric 1
`sulmet 198.1!!.96.fl. metric 2
`nulrnet 130. 9.32.9. netxtia
`M1’: sanding v1 update tn 255.255.255.255 via Sm-ialfl <13l3.1B.61.1)
`
`To turn off RIP debugging, type no debug ip rip and press Enter
`(otherwise the update messages will drive you crazy if you are trying
`to work on the router).
`SEE ALSO
`
`F For izzfimmzrion on /Jaw rvlrters‘ work /md 1/sing routing protocol; to [mild routing miller, ma
`page 82.
`
`Configuring IGRP
`
`Because RIP is limited to routes of less than 16 hop counts, interme—
`diate and large internetworks need a routing protocol that can handle
`the scale of the network. IGRP is a distance vector routing protocol
`
`211
`
`

`
`Configuring a Routing Protocol CHAPTEH11
`
`PART III
`
`like (RIP) that uses several metrics such as delay, bandwidth, and
`reliability. IGRP doesn’t use hop count as a meuic but it can provide
`routing information for a path of up to 25 5 hops, which makes it
`ideal for large internetworks.
`
`Configuring IGRP is similar to configuring RIP. You must enable
`the IGRP protocol and specify the major ll’ networks that are
`directly connected to the routers interfaces. However, because IGRP
`is used on larger internetworks (such as a complete corporate net
`work), you must specify the autonomous system number for the
`autonomous system (AS) that the router belongs to. Several different
`networks (Class A, B, or C) can be part of a particular autonomous
`system. Autonomous systems are tied together by core routers that
`run an Exterior Gateway Protocol, such as Border Gateway Protocol
`(BGP).
`
`Configuring IGHP
`
`1. At the privileged prompt, type config -t, and then press Enter.
`You are placed in the Global Configuration mode.
`
`. At the config prompt, type router igrp [autonomous system numa
`her] , where the autonomous system number is the AS number
`assigned to the AS to which your router belongs. For example,
`router igrp 10 would enable IGRP routing and specify the AS
`number 10. After entering the command, press Enter.
`
`. Type network [major network number] at the config prompt. The
`major network number is the network address for a Class A, B, or
`C network that is directly connected to the router. In this case,
`you are connected to one major network, 130.l0.0.0, so the
`command would be network 130.1u.0.0 (see Figure 11.10). Press
`Enter to continue.
`
`. Repeat the network [major neLwork number] for each IP network
`that the router is directly connected to. For example, if different
`Class C networks are connected to several Ethernet interfaces,
`you must repeat the network command for each of the network
`addresses for these Class C networks.
`'
`
`Séé'Appendrx C‘
`Cisco Route‘
`Spéeific_atrons,.
`rnatienion the 7500 series
`'ofCisco that might be”us‘ed‘
`as Core routers,"
`
`C
`
`«
`
`.
`
`212
`
`

`
`PART II Routing LAN Protocols
`
`CHAPTER 11 Configuring IP Routing
`
`npeycilnnnfia e
`9
`1-nutsr
`gr]:
`.. npaya (nanf
`tr unnfiiun)-fition unqmandga ans ye)‘ line.
`peyecmmMy-;-uutex-)tzummrk 13a.1a.a.n
`. p.y..<=unrrg—;-sum-)u
`
`»
`
`_
`
`End um. cumzz.
`
`5. VVhen you have entered the directly connected networks, press
`Ctrl+Z to end the configuration session.
`
`You can also use the show commands (and variations of these com—
`rnands related to IGRP) that were discussed in the section on RIP
`routing. For example, the Show ip route command now shows the
`routing table built by IGRP (see Figure 11.11). Network addresses
`marked with a C are directly connected to the router; addresses
`marked with an I are those discovered by IGRP.
`
`uyulslu in ruucu
`11 > IIGP
`as: G *' Imnnactnd. 3 " static, I " IGRP. R 7 RH’. H * nubile.
`D 7 EIGRP, Ell ~ EIGRP cxtcrnal, 0 — OSPF.
`Ifl — OSPF inter area
`H1 - 03?)’ NEW] external type 1. NZ - OSFP NSSR external type 2
`E1 — 08.?!’ external type 1, K2 — osvn oxtmnual typa 2,
`I1 — Eu?
`1 - IS-IS, L1 - Is—ls lalml-1, L2 — 1s—xs 1aun1—2,
`as — nnurlirlntn default
`ll — pa)-usexl gratin: nnlte, n — mm
`ntui-my of last rasnrl. is mu; snt
`1JB.1l!..B/19 is suhllltted, fl subtler:
`i3fl.1B.32.B is directly nannentad. Ethel-nnI:B
`130.1B.6!.E is directly nannacted. Sndalfl
`1.39d.1U.96.lI [1HB/71flD] via 13B..1B.E4.2, 09581287, Seriatlfi
`npayalll
`
`3
`
`IGRP sends updates every 90 seconds (as opposed to RIP’s 30-second
`interval). Routes not confirmed for 630 seconds are flushed from the
`routers routing table. You can View this information using the show
`ip route command.
`
`To View a summary of the IGRP routing update messages as they exit
`and enter the router, use the debug ip ig rp events command at the
`Privileged prompt. Figure 11.12 shows the results of this command.
`
`lf you want to see information related to the update messages such as
`the rnenic used (a number representing a value based on all the
`IGRP metrics), use the debug ip igrp transaction command. Figure
`11.13 displays the results of this command.
`
`
`
`...v..wi..;«4~s»;««:w;»~.-ww»«»«:e;~<:::v'*""*_..%..._t,:3‘:-swzmzesizviww-::r;1~::r:.Tv‘*_._“'L:::r
`
`i press Enter.’
`
`213
`
`

`
`Dynamic Houting Versus Static Routing CHAPTER11
`
`PART III
`
`x 1-p an m:
`1
`uyaild bin
`- v wait ialnligs :15 been:
`: yeeniunrl update rum 1ClD.1B.E4.2 an Sal-ialfi
`:
`: Umlatr. rznntains 1 interior, 8 2:]/nhan, and la ext-via» routes.
`(GNP: Total x-nutns in updattz: 1
`:
`IGI'll’= sanding u]|IIa1.‘u tu 255.255.255.255 -mi athnunucla ¢1:aa.m.32.1>
`=
`:
`IGRP: Uprlnt: cuntains 2 iuterlur, B syatun, and la axtm-inn routes.
`:
`IGRP: Inbnl ruutcs in update: 2
`:
`IGHFE uending ujnlnht
`(:1: 255.255.255.255 uiu Sarialfl (13G.1B.$d.i)
`:
`IGRP: Update contains 1 :l.ntur1ar. E ::!M:nIw. and B uxterinr routes.
`II:
`IGRP: Ionl route: in update.’ 1
`: mm‘: received update Eran 13Ia.1u.r:4.2 un Sm-ialla
`‘
`IGBP: Update contains 1 tints:-inn-, E syutan, and E e)¢tm.<inu 1-nukes.
`‘
`IGRP: ‘Intel rnuhas in updabn: 1
`:
`!GRP: sending lI}II.lrll.E tn 255.255.255.255 uia Etluu-nntfl (13H.iB_32.1)
`'
`IGl'lP= Update contains 2 :i.uLex-luv. 3 system. and B axtux-inn‘ rnuta-.:.
`.
`IGRP! Intal routes in update: 2
`. 1Gl'(P= sanding uvdate to 255.255.255.255 uia Surinlfl (1JB.1I!.E4.1)
`-
`IGRP: Update contain: 1 interior, a cyaenn, and 8 nxl:arim< rnutns.
`.
`IGRP: Intul routes in update: 1
`tom: 2-annivell npdatn Eran 1'.iB.1l6.64.2 an samlala
`IGHP: Umlate cuntnins 1 in
`I‘, B Ry-Item, and I2) axtariuu rautoc.
`IGl'iI'= Total n-uuhw in u dn
`
`nyuyuflflahug ip igrp |§l‘fllI5fl(:tifll’|
`-
`u u
`[GNP Dfiuluucl dzhugginu is an
`5:
`IGRPR (landing update to 255.255.255.255 via Etlvarnetfl (13fl.1B.32.1)
`dD3l):
`uubnel: 13B.1B.E‘l.K,
`l7u:C|‘ic='7BBB
`2
`cuhlmt 13B.1B.96.B, ne<-.rie'~?1Bfl
`:
`IGRP: sending update to 255.255.255.255 Ulla Burialfl (19I3.1B.G4.i)
`'
`suhnut 13B.1B.32.3.
`lIoh‘ii:=11fli]
`Jtamaiuail Ilprlata from 13fl.1B.64.2 nn Sex-ialfl
`96
`Evil: 71
`ueiylnhur LIBB)
`
`see ALSO
`E-.~ Forbm:kg7mI11rIiIy‘?2772mtianoI1IGRI-Lreepngepg.
`For (112 ovemiew afE.vtc7'im' G/zteway Protocols, seepage 95'.
`
`‘and the metiibyailue
`used}: g
`‘-
`’
`'
`’
`
`I
`
`yna