© 2011 itt educational services inc. nt-2640 advanced networking: unit 4: slide 1 unit 4 ip routing...

© 2011 ITT Educational Services Inc. NT-2640 Advanced Networking: Unit 4: Slide 1

Unit 4

IP Routing with Connected, Static, and RIP-2 Routes

Chapters 12-14

NT2640.U4.PS1

Class Agenda 10/10/15• Learning Objectives• Unit 3: Presentation and Discussions • Chapter 12-14• Discussion on Lab Activities.• Discussion on Assignments.• Break Times. 10 Minutes break in every 1 Hour.• Note: Submit all Assignment and labs due

today.


Objectives

In this unit, students will demonstrate an: •Understanding of the IP Routing Process including the IP Route Selection Process

•Understanding of IP Connected and Static Routes including Configuration and Verification Steps

•Understanding of the Definition of IP Subnet

•Understanding of the Distance Vector versus Link-State Routing Protocols

•Understanding of the Cisco IOS IP RIP v2 Configuration and Verification Steps

•Understanding of the Cisco IOS Administrative Distance Default Numeric Weights


IP Routing and Analyzing IP Subnets

Chapters 12 & 13

NT2640-U4-PS1

Chapter 1

4

IP Routing

• IP routing is also call called IP forwarding• It is the process use by routers to send

packets at the network layer. • IP routing protocols refers to the protocols the

routers use to implement the routing tables

© 2011 ITT Educational Services Inc. NT-2640 Wan Technologies: Unit 4: Slide 5

2.6

Figure 2.7 Hop-to-hop delivery

2.7

Figure 2.9 Source-to-destination delivery

IP Routing and Addressing

• IP routing depends on the rules of IP addressing, with one of the original core design goals for IP addressing being the creation of efficient IP routing.

• IP routing defines how an IP packet can be delivered from the host at which the packet is created to the destination host.

• IP addressing conventions group addresses into consecutively numbered sets of addresses called subnets, which then aids the IP forwarding or IP routing process.

• This book uses the terms IP routing and IP forwarding as synonymous terms.


19.9

Figure 22.4 Default method

Routing Steps of a Router1. For each received frame, it uses the data-link trailer frame check sequence

(FCS) field to ensure that the frame had no errors; if errors occurred, discard the frame (and do not continue to the next step).

2. Checks the frame’s destination data link layer address, and process only if addressed to this router or to a broadcast/multicast address.

3. Discards the incoming frame’s old data-link header and trailer, leaving the IP packet.

4. Compares the packet’s destination IP address to the routing table, and find the route that matches the destination address. This route identifies the outgoing interface of the router, and possibly the next-hop router.

5. Determines the destination data-link address used for forwarding packets to the next router or destination host (as directed in the routing table).

6. Encapsulates the IP packet inside a new data-link header and trailer, appropriate for the outgoing interface, and forward the frame out that interface.


Example of the IP Routing Process


IP Routing Process “Of Previous Slide”

1. R1 checks the FCS, and the frame has no errors.

2. R1 finds its own Fa0/0 interface MAC address in the frame’s destination MAC address field, so R1 should process the encapsulated packet.

3. R1 discards the old data-link header and trailer, leaving the IP packet .

4. R1 compares the destination IP address (172.16.3.3) to R1’s routing table, finding the matching route shown in the figure, with outgoing interface Fa0/1 and next-hop router 172.16.2.252.

5. R1 needs to find the next-hop device’s MAC address (R2’s MAC address), so R1 looks and finds that MAC address in its ARP table.

6. R1 encapsulates the IP packet in a new Ethernet frame, with R1’s Fa0/1 MAC address as the source MAC address, and R2’s Fa0/0 MAC address (per the ARP table) as the destination MAC address. R2 sends the frame.


19.13

Figure 22.5 Simplified forwarding module in classless address

Example of the IP Routing Process


Example IP Addressing Design


IP Forwarding by Matching the Most Specific Route

• Any router’s IP routing process requires that the router compare the destination IP address of each packet with the existing contents of that router’s IP routing table.

• Often, only one route matches a particular destination address. However, in some cases, a particular destination address matches more than one of the router’s routes.

• Some legitimate and normal reasons for the overlapping routes in a routing table


Routes to Directly Connected Subnets

• A router automatically adds a route to its routing table for the subnet connected to each interface, assuming that the following two facts are true: The interface is in a working state—in other words, the

interface status in the show interfaces command lists a line status of up and a protocol status of up.

The interface has an IP address assigned, either through the ip address interface subcommand or by using DHCP client services.


show ip route

• The show ip route command confirms an IP address is added a route to routing table.

• no ip subnet-zero command configured on a router, enable a router rejects any ip address command that uses an address/mask combination for the zero subnet.


Static Routes

• Routers use three main methods to add routes to their routing tables: connected routes, static routes, and dynamic routing protocols.

• Routers always add connected routes when interfaces have IP addresses configured and the interfaces are up and working.


Classful and Classless Routing

• Cisco routers have two configurable options for how a router uses an existing default route: classless routing and classful routing.

• Classless routing causes a router to use its default routes for any packet that does not match some other route.

• Classful routing places one restriction on when a router can use its default route, resulting in cases in which a router has a default route but the router chooses to discard a packet rather than forwarding the packet based on the default route.


Comparing the Use of the Terms Classless and Classful

As Applied To Classful ClasslessAddresses Addresses have three parts:

network, subnet, and host.Addresses have two parts: subnet or prefix, and host.

Routing protocols Routing protocol does not advertise masks nor support VLSM; RIP-1 and IGRP.

Routing protocol does advertise masks and support VLSM; RIP-2, EIGRP, OSPF.

Routing (forwarding)

IP forwarding process is restricted in how it uses the default route.

IP forwarding process has no restrictions on using the default route.


Chapter 13

Analyzing Existing Subnets


IP Packet Routing

• Key pieces of information about the subnet:The subnet IDThe subnet broadcast addressThe subnet’s range of usable unicast IP

addresses


Defining a Subnet

• An IP subnet is a subset of a classful network, created by choice of some network engineer.

• However, that engineer cannot pick just any arbitrary subset of addresses; instead, the engineer must follow certain rules, like the following: The subnet contains a set of consecutive numbers The subnet holds 2H

numbers, where H is the number of host bits defined by the subnet mask Two special numbers in the range cannot be used as IP addresses: The first (lowest) number acts as an identifier for the subnet (subnet ID) The last (highest) number acts as a subnet broadcast address The remaining addresses, whose values sit between the subnet ID and

subnet broadcast address, are used as unicast IP addresses


Address Structure: Class B Network, /18 Mask

• All four subnets will have the structure shown in the figure, so all four subnets will have 214 – 2 host addresses.


Subnet ID Concepts

• A subnet ID is simply a number used to succinctly represent a subnet.

• When listed along with its matching subnet mask, the subnet ID identifies the subnet, and can be used to derive the subnet broadcast address and range of addresses in the subnet.

• Rather than having to write down all these details about a subnet, you simply need to write down the subnet ID and mask, and you have enough information to fully describe the subnet.

• The subnet ID appears in many places, but it is seen most often in IP routing tables.


Summary of Subnet ID Key Facts

Definition A number that represents the subnet

Numeric value First (smallest) number in the subnet

Literal synonyms Subnet number, subnet address, prefix, resident subnet

Common-use synonyms Network, network ID, network number, network address

Typically seen in… Routing tables, documentation


The Subnet Broadcast Address

• The subnet broadcast address has two main roles: to be used as a destination IP address for the purpose of sending packets to all hosts in the subnet, and as a means to find the high end of the range of addresses in a subnet.

• The original purpose for the subnet broadcast address was to give hosts a way to send one packet to all hosts in a subnet, and to do so efficiently.


Binary Practice Problems

• To find the subnet ID using binary math. The following written process summarizes those steps in written form for easier reference and practice:

Step 1. Convert the mask to prefix format to find the length of the prefix (/P) and the length of the host part (32 - P).

Step 2. Convert the IP address to its 32-bit binary equivalent

Step 3. Copy the prefix bits of the IP address

Step 4. Write down 0s for the host bits

Step 5. Convert the resulting 32-bit number, 8 bits at a time, back to decimal


Subnet Analysis for Address 8.1.4.5, Mask 255.255.0.0

Prefix Length /16 11111111 11111111 00000000 00000000

Address 8.1.4.5 00001000 00000001 00000100 00000101

Subnet ID 8.1.0.0 00001000 00000001 00000000 00000000

Broadcast Address 8.1.255.255 00001000 00000001 11111111 11111111


Practice Problem 1

Table 13-4 Subnet Analysis for Subnet with Address 130.4.102.1, Mask 255.255.255.0

Prefix Length /24 11111111 11111111 11111111 00000000

Address 130.4.102.1 10000010 00000100 01100110 00000001

Subnet ID 130.4.102.0 10000010 00000100 01100110 00000000

Broadcast Address 130.4.102.255 10000010 00000100 01100110 11111111


Practice Problem 2


Prefix Length /24 11111111 11111111 11111111 00000000

Address 199.1.1.100 11000111 00000001 00000001 01100100

Subnet ID 199.1.1.0 11000111 00000001 00000001 00000000

Broadcast Address

199.1.1.255 11000111 00000001 00000001 11111111


Practice Problem 3


Prefix Length /22 11111111 11111111 11111100 00000000

Address 130.4.102.1 10000010 00000100 01100110 00000001

Subnet ID 130.4.100.0 10000010 00000100 01100100 00000000

Broadcast Address

130.4.103.255 10000010 00000100 01100111 11111111


Practice Problem 4


Prefix Length /27 11111111 11111111 11111111 11100000

Address 199.1.1.100 11000111 00000001 00000001 01100100

Subnet ID 199.1.1.96 11000111 00000001 00000001 01100000

Broadcast Address

199.1.1.127 11000111 00000001 00000001 01111111


Analysis with Easy Masks

• With three easy subnet masks in particular, finding the subnet ID and subnet broadcast address requires only easy logic and literally no math. Three easy masks exist:

Class A: 255.0.0.0

Class B: 255.255.0.0

Class C: 255.255.255.0• These easy masks have only 255 and 0 in decimal. In

comparison, difficult masks have one octet that has neither a 255 nor a 0 in the mask, which makes the logic more challenging.


Practice Problems: Find Subnet ID and Broadcast, Easy Masks

IP Address Mask Subnet ID Broadcast Address1 10.77.55.3 255.255.255.0

2 172.30.99.4 255.255.255.0

3 192.168.6.54 255.255.255.0

4 10.77.3.14 255.255.0.0

5 172.22.55.77 255.255.0.0

6 1.99.53.76 255.0.0.0


Reference Table: DDN Mask Values, Binary Equivalent, Magic Numbers, and

Prefixes

Prefix, interesting octet 2

/9 /10 /11 /12 /13 /14 /15 /16


/17 /18 /19 /20 /21 /22 /23 /24


/25 /26 /27 /28 /29 /30

Magic Number

128 64 32 16 8 4 2 1

DDN mask in the interesting octet

128 192 224 240 248 252 254 255


Chapter 14

Routing Protocol Concepts and RIP-2 Configuration


Routing Protocol Overview

• IP routing protocols have one primary goal: to fill the IP routing table with the current best routes it can find.

• The goal is simple, but the process and options can be complicated. • Routing protocols help routers learn routes by having each router advertise

the routes it knows. • Each router begins by knowing only connected routes. • Then, each router sends messages, defined by the routing protocol, that list

the routes. • When a router hears a routing update message from another router, the

router hearing the update learns about the subnets and adds routes to its routing table.

• If all the routers participate, all the routers can learn about all subnets in an internetwork.


RIP-2 Basic Concepts

• Routers using RIP-2 advertise a small amount of simple information about each subnet to their neighbors.

• Their neighbors in turn advertise the information to their neighbors, and so on, until all routers have learned the information.

• It works a lot like how rumors spread in a neighborhood, school, or company:

You might be out in the yard, stop to talk to your next-door neighbor, and tell your neighbor the latest gossip. Then, that neighbor sees his other next-door neighbor, and tells them the same bit of gossip—and so on, until everyone in the neighborhood knows the latest gossip.

• Distance vector protocols work the same way, but hopefully, unlike rumors in a real neighborhood, the rumor has not changed by the time everyone has heard about it.


Interior and Exterior Routing Protocols

IP routing protocols fall into one of two major categories: • Interior Gateway Protocol (IGP): A routing protocol that was

designed and intended for use inside a single autonomous system

• Exterior Gateway Protocol (EGP): A routing protocol that was designed and intended for use between different autonomous systems


Routing Protocol Types/Algorithms

Class/Algorithm IGPs

Distance vector RIP-1, RIP-2, IGRP

Link-state OSPF, Integrated IS-IS

Balanced hybrid (also called advanced distance vector) EIGRP


Interior IP Routing Protocols Compared

Feature RIP-1 RIP-2 EIGRP OSPF IS-IS

Classless No Yes Yes Yes Yes

Supports VLSM No Yes Yes Yes Yes

Sends mask in update No Yes Yes Yes Yes

Distance vector Yes Yes No1 No No

Link-state No No No1 Yes Yes

Supports autosummarization Yes Yes Yes No No

Supports manual summarization No Yes Yes Yes Yes

Proprietary No No Yes No No

Routing updates sent to a multicast IP address

No Yes Yes Yes N/A

Supports authentication No Yes Yes Yes Yes

Convergence Slow Slow Very fast Fast Fast


Class Exercise

• IP Subnetting II Small Group Exercise in class


Lab Activities.

• Complete Unit 4 Lab in class.• All answers to overdue labs should be

submitted in the next class.


Assignment

• Unit 4 assignment will be given in class.

• Reading Assignment: Read chapter 15 and 16


© 2011 itt educational services inc. nt-2640 advanced networking: unit 4: slide 1 unit 4 ip routing...

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ip routing protocols

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