Contents
Introduction xxiii
Chapter 1 Topology and Router Configurations
Understanding the Role of Routers in
Networks
The Router Interface
Network Layer Addresses
Datagrams
MAC Addresses
IP Address Formats
Network Reference Models
Understanding Topology and Router
Configurations
RouterA's Configuration
RouterB's Configuration
RouterC's Configuration
Understanding What a Router Does
Sample Network
How a Router Knows What to Do
Choosing Your Routing Protocol
Understanding How Forwarding Decisions
Are Made
Performing Longest Match Lookups
Forwarding Decisions for Multipoint
Interfaces
End Systems Sending Packets to Other Subnets
Summary
Chapter 2 Routing Metrics and Distances
Primary Activities of Convergence
Viewing the Invalid Timers in a Routing Table
Viewing an Expired Invalid Timer in a Routing
Table
Router Still Uses a Path
Understanding Convergence
Parallel Paths
The Effect ofParallel Paths on
Convergence
Looking at Parallel Paths in a Routing
Table
Convergence in Action
The Routing Table After Convergence
Step-by-Step Review of Convergence
Debug Messages and Reality
When Holddown Is Initiated
Understanding Parallel Paths and Their Effect on
Packet Forwarding
Process Switching Versus Fast Switching
Configuring Process Switching
Configuring Fast Switching
Understanding the Role of Split Horizon
Routing Advertisements with Split Horizon
Enabled
Routing Advertisements with Split Horizon
Disabled
Routing Loops Caused by Disabling Split
Horizon
Loss of a Connected Route Versus a Dynamic
Route
Split Horizon's Effect on Multipoint WAN
Interfaces
Using Subinterfaces to Avoid Problems Caused by
Split Horizon
Poison Reverse and Triggered Updates
IGRP Routing Metrics (Variables) and Cisco
Administrative Distances
IGRP Metrics (Variables)
Administrative Distances
Running Multiple Routing Protocols
Concurrently
Altering IGRP's Bandwidth and Delay
Variables
Problems with Manipulating the Delay
Variable
Understanding the Effects of Manipulating the
Delay Variable
Vnderstanding the Effects of Manipulating the
Bandwidth Variable
Calculating IGRP Metrics
Summary
Chapter 3 Discontiguous Networks, Summarization,
and Subnet 0
Introduction to Terminology
Discontiguous Networks Using RIP and
IGRP
Understanding How a Router Derives the Correct
Masks
Understanding Summarization (Summarized
Routes)
Understanding Subnet 0
Summarized Routes Versus Subnet 0
Summarization Caused by Discontiguous
Networks in Action
RIP Cannot Reach Discontiguous Subnets
Discontiguous Networks, Subnet 0, and
Summarization Using IGRP
Discontiguous Networks Using Two Routers
Discontiguous Networks Using Three
Routers
When Connectivity Is Possible
When Connectivity Is Not Possible
Alternating Paths for the First Ping
Using Other Routing Protocols
Using Summarization as a Tool
Summary
Chapter 4 Using IP Unnumbered and VLSM
Understanding IP Unnumbered
IP Unnumbered Causes Host Routes and Lost
Connectivity
Host Routes
Hosts Routes Using DDR
Configuring IP Unnumbered on Serial
Interfaces
RIP and IGRP Behave the Same
RIP with IP Unnumbered Configured
Properly
Displaying the Routes
Sending Routing Updates
Pinging the Interfaces
RIP with IP Unnumbered Configured
Improperly
Examples of Routing Updates
Host Route Problem
Lost Routes Problem
Using a Different Subnet Mask and a Different
Major Net
Understanding VLSM
VLSM Using RIP and IGRP
VLSM Experiment Using Two Routers
VLSM Experiment Using Three Routers
Cbrrectly Configuring VLSM Blocked
Routes
VLSM Summary
Summary
Chapter 5 Oefault Routing
Introduction to Default Routing
Gateway of Last Resort
Gateway of Last Resort for a Non-Local
Domain
Gateway of Last Resort Fails for a Local
Domain
Gateway of Last Resort Still Works When Links
Fail
Using IP Classless
In Review
Using Default and Static Routes in Complicated
Networks
Using Static Routes
Dealing with Too Much Default Routing
Information
Fixing a Default Gateway Loop
The 0.0.0.0 Default Route
RIP and 0.0.0.0
Using 0.0.0.0 with IGRP
What to Do Instead of Using 0.0.0.0 with
IGRP
Using End Systems with Multiple Local
Gateways
ICMP Router Discovery Protocol (IRDP) RFC
1256
End Systems Using RIP
Cisco's Hot Standby Router Protocol (HSRP)
Using Floating Static Routes
Summary
Chapter 6 IP Troubleshooting Scenarios
Developing a Troubleshooting Routine
Using a Troubleshooting Scenario
Checking the Available Routes
Tracing the Route
Using Extended Pings to Track Connectivity
Other Possible Problems
An ARP Problem
Validating End System Routing Tables
Summary
Chapter 7 Bridging IP Between Dissimilar Media
Translational Bridging
MSBVersusLSB
?Bit Swapping MAC Addresses
ARP Explained
Translating Bridges and ARP Frames
ARP in Action
Vendor-Specific Solutions to ARP
Static ARPs
Displaying the Parameters ofthe ARP.EXE
Command
Displaying the Current ARP Entries
How to Create a Static ARP Entry
and Display It
Deleting Static ARP Entries
Summary
Chapter 8 Hexadecimal and Binary Numbering and
IP Addressing
Binary Numbering Versus Decimal
Numbering
Hexadecimal Numbering Versus Decimal
Numbering
Introduction to the 32-B it IP Address
Classes of Addresses
Default Subnet Masks for Class A, B, C, and D
Addresses
Understanding Subnet Masks, Subnetting, and
Supernetting
Determining What Subnet Is Being Used
The Shorthand Subnet Mask Indicator
Introduction to Supernetting
Calculating Subnet and Host Combinations
Summary
AppendixA RFCs
How RFCs Work
RFCs Recommended for Further Study
RFC 2235: Hobbes' Internet Timeline
RFC 2200: Internet Official Protocol
Standards
RFC 2151: A Primer on Internet and TCP/IP Tools
and Utilities
RFC 2101: IPv4 Address Behavior Today
RFC 2031: IETF-ISOC Relationship
RFC 2028: The Organizations Involved in the IETF
Standards Process
RFC 2027: IAB and IESG Selection, Confirmation,
and Recall Process: Operation of the Nominat-
ing and Recall Committees
RFC 2026: The Internet Standards Process:
Revision 3
RFC 2008: Implications ofVarious Address Alloca-
tion Policies for Internet Routing
RFC 1935: What Is the Internet, Anyway?
RFC 1925: The Twelve Networking Truths
RFC 1923: RIPvl Applicability Statement for His-
toric Status
RFC 1918: Address Allocation for Private
Internets
RFC 1917: An Appeal to the Internet Community
to Return Unused IP Networks (Prefixes) to the
IANA
RFC 1878: Variable Length Subnet Table for
IPv4
RFC 1812: Requirements for IP Version 4
Routers
RFC 1631: The IP Network Address Translator
(NAT)
RFC 1601: Charter ofthe Internet Architecture-
Board (IAB)
RFC 1580: Guide to Network Resource
Tools
RFC 1393: Traceroute Using an IP Option .
RFC 1256: ICMP Router Discovery
Messages
RFC 1180: A TCP/IP Tutorial
RFC 1178: Choosing a Name for Your
Computer
RFC 1149: A Standard for the Transmission of IP
Datagrams on Avian Carriers
RFC 1058: Routing Information Protocol
RFC 826: An Ethernet Address Resolution
Protocol
RFC 1700: Assigned Numbers
RFC 1534: BOOTP
RFC 2283, RFC 1966, RFC 1965, RFC 1774, RFC
1773, RFC 1772, RFC 1771, RFC 1745: Border
Gateway Protocol V4 (BGP4)
RFC 1817, RFC 1520, RFC 1519, RFC 1518, RFC
1517: Classless Interdomain Routing
(CIDR)
RFC 2132, RFC 2131, RFC 1534: Dynamic Host
Configuration Protocol (DHCP)
RFC 2308, RFC 2230, RFC 2219, RFC 2182, RFC
2181, RFC 2136, RFC 2052, RFC 1996, RFC
1995, RFC 1912, RFC 1794, RFC 1713: Do-
main Name System (DNS)
RFC 2178, RFC 1745, RFC 1587, RFC 1586, RFC
1585, RFC 1584: Open Shortest Path First
(OSPF)
RFC 1931, RFC 1293: Reverse Address Resolution
Protocol (RARP) Inverse RARP
RFC 2092, RFC 2091, RFC 1723, RFC 1722, RFC
1721, RFC 1582, RFC 1581: RIP
RFC 2072, RFC 2071: Router Renumbering
RFC 2001: TCP/IP (TCP) Slow Start
RFC 1470: TCP/IP Debugging Tools
Summary
Index
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