Guide to TCP/IP, Third Edition : Guide to TCP/IP, Third Edition Chapter 10:
Routing in the IP Environment
Objectives : Routing in the IP Environment 2 Objectives Understand how basic routing works
Describe various routing characteristics
Understand interior gateway protocols, such as RIP, OSPF, and EIGRP
Understand BGP, an exterior gateway protocol
Describe how to manage routing on an in-house internetwork
Objectives (continued) : Routing in the IP Environment 3 Objectives (continued) Be aware of the challenges associated with redistributing a network from a classless protocol to a class-oriented protocol
Describe factors involved in choosing a routing protocol for your wide area network
Describe router connections on internal and external networks, including the Internet
Objectives (continued) : Routing in the IP Environment 4 Objectives (continued) Understand the importance of securing routers and routing protocols
Explain basic router diagnostic troubleshooting concepts, tools, and techniques
Understanding Routing : Routing in the IP Environment 5 Understanding Routing Routing table
Database that lives in the memory of the router
Compilation of information about all the networks that the router can reach
Slide 6 : Routing in the IP Environment 6
How Entries Are Placed in the Routing Table : Routing in the IP Environment 7 How Entries Are Placed in the Routing Table Route entry can be placed in a routing table in three basic ways
Through direct connection
It can be manually configured
An entry can be placed in a routing table is dynamically, by using a routing protocol
Routing Protocols and Routed Protocols : Routing in the IP Environment 8 Routing Protocols and Routed Protocols Routing protocols
Used to exchange routing information
Routing Information Protocol (RIP) and OSPF are routing protocols
Routed protocols
Layer 3 protocols that are used to get packets through an internetwork
Grouping Routing Protocols : Routing in the IP Environment 9 Grouping Routing Protocols Interior gateway protocols (IGPs)
Routing protocols used inside a routing domain are called interior
Exterior gateway protocols (EGPs)
Routing protocols used to connect these routing domains
Distance vector and link-state
Used to communicate
Distance Vector Routing Protocols : Routing in the IP Environment 10 Distance Vector Routing Protocols RIP
Interior Gateway Routing Protocol (IGRP)
Border Gateway Protocol (BGP) also is a distance vector routing protocol
Slide 11 : Routing in the IP Environment 11
Link-State Routing Protocols : Routing in the IP Environment 12 Link-State Routing Protocols Differ from distance vector routing protocols in two ways
They do not route by rumor
They do not periodically broadcast their entire tables
Slide 13 : Routing in the IP Environment 13
Routing Characteristics : Routing in the IP Environment 14 Routing Characteristics Network
Converged when all the routers know a loop-free path to get to all other networks
Ideally should be in a converged state
Split horizon
Used to speed up the process of convergence and resolve the counting-to-infinity problem
Poison reverse
Technique for assigning costs to routes designed to prevent routing loops
Slide 15 : Routing in the IP Environment 15
Routing Characteristics (continued) : Routing in the IP Environment 16 Routing Characteristics (continued) Time to Live
Ensures that packets cannot loop endlessly through a network
Defined in the Network layer header
Multicast Versus Broadcast Update Behavior
Routers can be configured to forward multicasts
RIPv1 sends broadcast updates
RIPv2 can send multicast updates
ICMP Router Advertisements : Routing in the IP Environment 17 ICMP Router Advertisements Some routers
Can be configured to send periodic ICMP Router Advertisement packets
Periodic ICMP Router Advertisements
Allow hosts to learn passively about available routes
Unsolicited ICMP Router Advertisements
Sent periodically to the all-hosts multicast address 224.0.0.1
Black Holes : Routing in the IP Environment 18 Black Holes Occurs on a network when
ICMP is turned off and
Router discards packets without sending any notification about its actions
Slide 19 : Routing in the IP Environment 19
Areas, Autonomous Systems, and Border Routers : Routing in the IP Environment 20 Areas, Autonomous Systems, and Border Routers OSPF utilizes areas
To reduce the number of entries in the link-state database
OSPF specification
Defines the need for a backbone area, Area 0
Autonomous systems (ASs)
Groups of routers under a single administrative authority
Slide 21 : Routing in the IP Environment 21
Slide 22 : Routing in the IP Environment 22
Interior Gateway Protocols : Routing in the IP Environment 23 Interior Gateway Protocols Used to exchange routing information within an AS
Also are referred to as intra-domain routing protocols
RIP
Basic distance vector routing protocol
Two versions: RIPv1 and RIPv2
Communications are UDP based
RIP-based routers send and receive datagrams on UDP port number 520
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Open Shortest Path First : Routing in the IP Environment 27 Open Shortest Path First Defined in RFC 2328
The premier link-state routing protocol used on TCP/IP networks
Based on
Configurable values (metrics) that may be based on network bandwidth, delay, or monetary cost
Slide 28 : Routing in the IP Environment 28
Open Shortest Path First (continued) : Routing in the IP Environment 29 Open Shortest Path First (continued) Six basic types of LSAs:
Type 1 (Router Links Advertisement)
Type 2 (Network Links Advertisement)
Type 3 (Network Summary Link Advertisement)
Type 4 (AS Boundary Router Summary Link Advertisement)
Type 5 (AS External Link Advertisement)
Type 7 (Not So Stubby Area Networks Advertisement)
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Slide 31 : Routing in the IP Environment 31
Enhanced Interior Gateway Routing Protocol : Routing in the IP Environment 32 Enhanced Interior Gateway Routing Protocol Interior Gateway Routing Protocol (IGRP)
Developed in the 1980s by Cisco Systems
Updated in the early 1990s (Enhanced Interior Gateway Routing Protocol)
Enhanced Interior Gateway Routing Protocol
Integrates the capabilities of link-state routing into a distance vector routing protocol
Border Gateway Protocol : Routing in the IP Environment 33 Border Gateway Protocol Exterior gateway protocols (EGP)
Used to exchange routing information between separate autonomous systems
Defined in RFC 904
Border Gateway Protocol (BGP) replaces EGP routing
Border Gateway Protocol (continued) : Routing in the IP Environment 34 Border Gateway Protocol (continued) Offers three types of routing operations
Inter-autonomous system routing
Intra-autonomous system routing
Pass-through autonomous system routing
When configured for intra-autonomous system routing
BGP routers are located within the same AS
Pass-through autonomous system routing
Enables BGP peer routers to exchange routing information across an AS that does not support BGP
Slide 35 : Routing in the IP Environment 35
Managing Routing on an In-House Internetwork : Routing in the IP Environment 36 Managing Routing on an In-House Internetwork IP routing protocols have a shortcoming
They do not discriminate between users, types of traffic, and so on
They only know how to get to a network
Policy-based routing addresses this shortcoming
Hybrid Networks : Routing in the IP Environment 37 Hybrid Networks What happens when you redistribute a network from a classless protocol to a class-oriented protocol that only understands the major network address but not the VLSM you’re using?
How can you convert the bandwidth, delay, load, reliability, and MTU size of EIGRP and IGRP into the simple hop counts that RIP uses?
Routing On and Off a Wide Area Network : Routing in the IP Environment 38 Routing On and Off a Wide Area Network If the network in question is relatively small
Consider using no routing protocol
Frame relay and ATM
Use virtual circuits
So one physical interface can actually be logically partitioned into several logical interfaces.
If your company also uses Novell’s IPX protocol
You may have to run one routing protocol for IP and another routing protocol for IPX
Mobile Users : Routing in the IP Environment 39 Mobile Users Mobile IP
Defined by the IETF in RFCs 2003 through 2006 and RFC 3220 (which obsoletes RFC 2002)
Local Area Mobility
Cisco proprietary feature that is similar to Mobile IP
Operates by using the routing table
Routing To and From the Internet : Routing in the IP Environment 40 Routing To and From the Internet BGPv4
The exterior routing protocol in use on the Internet
Should only be used by networks that connect to multiple Internet providers
Tracks hops between pairs of autonomous systems instead of tracking hop counts for actual routers
Securing Routers and Routing Behavior : Routing in the IP Environment 41 Securing Routers and Routing Behavior Securing routers
Turn off unnecessary services
Shut down unnecessary listening ports
Configure strong access security to prevent tampering
Secure physical access to the boxes
Securing routing protocols
Requires cooperation from the protocols themselves
Troubleshooting IP Routing : Routing in the IP Environment 42 Troubleshooting IP Routing ROUTE
View the host’s local routing table, and add and remove route entries
PING
Sends ICMP Echo messages and test connectivity
TRACERT
Sends ICMP echoes with incrementally increasing TTL values to identify the path to a destination
PATHPING
Utility used to discover path from host to destination
Summary : Routing in the IP Environment 43 Summary Routing protocols and routers
Provide a mechanism that can forward traffic from a sender’s subnet to an intended receiver’s subnet
Routers
Depend on various routing protocols to manage the packet forwarding process
Distance vector routing protocols such as RIP
Provides a crude metric of routing cost
Summary (continued) : Routing in the IP Environment 44 Summary (continued) The OSPF protocol
Supports much more sophisticated routing structures that break up a network into routing areas
Routing characteristics
Help to determine what kinds of routing protocols to use in specific applications
Managing routing on a complex network means
Understanding how and when to use exterior and interior routing protocols
Summary (continued) : Routing in the IP Environment 45 Summary (continued) Router tables define the topology and behavior of IP networks
Essential to manage router security and updates as safely as possible
Troubleshooting tools for inspecting and diagnosing routing problems through
Windows 2000, Windows Server 2003, and Windows XP IP host include route, tracert, ping, and pathping