CCIE Routing and Switching v4.0 Quick Reference (eBook), 2nd Edition.pdf

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Table of Contents
Chapter 1
General Networking Theory ...................2
Chapter 2
Bridging and LAN Switching ............... 11
Chapter 3
IP Addressing ........................................ 30
Chapter 4
IP Routing .............................................. 55
Chapter 5
Quality of Service (QoS).....................113
Chapter 6
Network Optimization ........................144
Chapter 7
WAN......................................................157
Chapter 8
IP Multicasting ....................................168
Chapter 9
Security ................................................185
Chapter 10
MPLS ....................................................204
Chapter 11
IPv6.......................................................217
Chapter 12
Implementing Layer 2 Technologies .226
Chapter 13
Implementing IPv4 .............................232
Chapter 14
Implementing IPv6 .............................241
CCIE Routing and
Switching v4.0
Quick Reference
Brad Ellis
Jacob Uecker
Steven Means
ciscopress.com
[2]
CCIE Routing and Switching v4.0 Quick Reference
Chapter 1
General Networking Theory
General Routing Concepts
Link-State and Distance Vector Protocols
Distance Vector
Examples: Routing Information Protocol Version 1 (RIPv1), RIPv2, Interior Gateway Routing Protocol (IGRP)
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Features periodic transmission of entire routing tables to directly connected neighbors
Mathematically compares routes using some measurement of distance
Features hop-count limitation
Link State
Examples: Open Shortest Path First (OSPF), Intermediate System-to-Intermediate System (IS-IS)
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Sends local connection information to all nodes in the internetwork.
Forms adjacencies with neighboring routers that speak the same protocol; sends local link information to
these devices.
Although this floods of information to all nodes, the router sends only the portion of information that deals
with the state of its own links.
Each router constructs its own complete “picture” or “map” of the network from all the
information received.
© 2011 Cisco Systems Inc. All rights reserved. This publication is protected by copyright.
Please see page 245 for more details.
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[3]
CCIE Routing and Switching v4.0 Quick Reference
Hybrid
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Example: Enhanced Interior Gateway Routing Protocol (EIGRP)
Features properties of both distance vector and link-state routing protocols
Path Vector Protocol
Example: Border Gateway Protocol (BGP)
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Path vector protocols are a subset of distance vector protocols; BGP uses path vectors or a list of all the
autonomous systems a prefix has crossed to make metric decisions and to ensure a loop-free environment.
In addition to the autonomous system path list, an administrator can use many other factors to affect the
forwarding or receipt of traffic using BGP.
Routing protocols use the Split horizon technique to help prevent routing loops. The split-horizon rule
states that an interface will not send routing information out an interface from which the routing
information was originally received. Split horizon can cause problems in some topologies, such as
hub-and-spoke Frame Relay configurations.
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Split Horizon
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Summarization
Summarization is the process in which the administrator collapses many routes with a long mask to form another
route with a shorter mask. Route summarization reduces the size of routing tables and makes the routing function
more efficient. Route summarization also helps to make networks more stable by reducing the number of updates
sent when subnets change state. Route summarization makes classless interdomain routing (CIDR) possible.
Variable-length subnet masking (VLSM) promotes the use of route summarization. Some dynamic routing protocols
engage in route summarization automatically for changes in a major classful network, whereas others do not.
For any routing protocol within the scope of the CCIE written exam, an administrator can disable any automatic
summarization that might occur and configure manual summarization.
To engage in route summarization, find all the left-most bits that are in common and create a mask that encompasses
them. An example follows.
© 2011 Cisco Systems Inc. All rights reserved. This publication is protected by copyright.
Please see page 245 for more details.
[4]
CCIE Routing and Switching v4.0 Quick Reference
The following routes exist in the routing table—all routes use a 24-bit mask:
10.108.48.0 = 00001010 01101100 00110000 00000000
10.108.49.0 = 00001010 01101100 00110001 00000000
10.108.50.0 = 00001010 01101100 00110010 00000000
10.108.51.0 = 00001010 01101100 00110011 00000000
10.108.52.0 = 00001010 01101100 00110100 00000000
10.108.53.0 = 00001010 01101100 00110101 00000000
10.108.54.0 = 00001010 01101100 00110110 00000000
10.108.55.0 = 00001010 01101100 00110111 00000000
Notice that the first 21 bits of the subnetwork IDs are all common. These can be masked off. You can use the single
route entry for all these subnetworks as follows:
10.108.48.0/21
Classful and Classless Routing Protocols
Classful routing protocols are considered legacy and do not include subnet mask information with routing updates.
Examples of classful routing protocols are RIPv1 and IGRP. Because subnet mask information is not included
in updates, consistency of the mask is assumed throughout the network. Classful routing protocols also feature
automatic summarization of routing updates when sent across a major classful network boundary. For example, the
10.16.0.0/16 network would be advertised as 10.0.0.0/8 when sent into a 172.16.0.0 domain.
Although BGP and EIGRP are not classful routing protocols, both engage in automatic summarization behavior by
default, and in that sense they act classful. The
no auto-summary
command is used to disable this behavior.
Classful routing protocols feature a fixed-length subnet mask (FLSM) because of their inherent limitations. The
FLSM leads to inefficient use of addresses and limits the network’s overall routing efficiency.
By default, classful routing protocols discard traffic bound for any unknown subnet of the major classful network.
For example, if your classful routing protocol receives traffic destined for 10.16.0.0 and it knows of only the 10.8.0.0
and 10.4.0.0 subnets in its routing table, it discards the traffic—even
if a default route is present!
The
ip classless
© 2011 Cisco Systems Inc. All rights reserved. This publication is protected by copyright.
Please see page 245 for more details.

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