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As with most other routing protocols, the best path to a destination is the path with the lowest metric. EIGRP has the ability to use several variables to compute the metric to a destination network. The first five listed above are those variables: bandwidth, delay, reliability, load, and MTU. Only bandwidth and delay are used by default. It is highly recommended that the defaults be maintained, because using other variables can result in unknown problems in your network.

The values of bandwidth and delay are determined from the bandwidth and delay values associated with the router interfaces. There are default values, but the values can be changed per interface with the bandwidth and delay subinterface commands.

The formula for computing EIGRP metrics follows:

Metric – {[K1 * Bandwidth + (K2 * Bandwidth)/(256 – Load) + K3 * Delay] * [K5/(Reliability + K4)]} * 256

The default K-values follow: K1 = 1; K2 = 0; K3 = 1; K4 = 0; K5 = 0; therefore, the metric formula can be simplified to:

Metric = (Bandwidth + Delay) * 256

Bandwidth = 10000000/Minimum bandwidth along path; and Delay = Sum of delays along path.

Therefore, the final metric formula becomes:

([10000000/Minimum bandwidth] + Sum of delay/10) * 256

Note: Formula uses the bandwidth in kilobits per second and delay as configured on the interface, which is in microseconds.

Metric example:

In this example, the total cost (metric) for Router_A to get to Network A through Router_B would be:

Minimum bandwidth = 128kbps
Total delay = 100 + 100 + 1000 = 1200/10 ms

([10000000/128] + 1200/10) * 256 = 20030720

The total cost to the same destination through Router_C follows:

Minimum bandwidth = 512kbps
Total delay = 1000 + 100 + 100 = 1200/10 ms

([10000000/512] + 1200/10) * 256 = 5030720

The path through Router_C has the lowest cost. Router_A would, therefore, choose the path through Router_C as the best path and put it in its routing table. This path would then be known as the successor (explained later).

In the above topology, the metric of Router_B to Network A would be 307200. Router_C would also have a metric of 307200 to Network A.

五 13 2010

about EIGRP (一）

Posted by admin in CISCO

Tags: eigrp | 3 Comments

http://www.cisco.com/web/learning/le31/le20/ssat/cim/tac_eigrp.html

Detailed Information

In this module, you will learn the basic concepts behind EIGRP. You will also do hands-on Configuration Labs to learn some fundamental concepts of EIGRP, and a Challenge Lab to test your troubleshooting knowledge.

Objectives:

At the end of this tutorial, you will be able to:

Describe the Reliable Transport Protocol and its function in EIGRP.
Summarize the neighbor discovery and recovery processes.
Discuss the process of EIGRP metric calculation and list the variables used.
Describe how EIGRP determines which paths are loop free.
Describe the process used to clear bad routes from EIGRP routing tables.
Describe the query process used to find paths to lost destinations.
Describe address summarization.
Summarize the administrative distance used by EIGRP to select routes.
Describe redistribution.
Discuss load balancing, over both equal- and unequal-cost paths.
Describe the three approaches to configuring default routing.

Labs(5):

Configuration Lab: Configuration, Updates and Acknowledgements, and Debugging
Configuration Lab: Load Balancing with Variance
Configuration Lab: Redistribution
Configuration Lab: Redistribution with an Autonomous System
Challenge Lab: EIGRP

DUAL Diffusing Update Algorithm (DUAL),

EIGRP, on the other hand, builds a topology table from information it learns from each of its neighbors. The information sent by EIGRP is nonperiodic and contains only new information. Using the Diffusing Update Algorithm (DUAL), EIGRP then chooses a best path (successor) and alternate loop-free paths (feasible successors) that allow for fast convergence. This information is kept in a topology table separate from the routing table. Upon losing a route to a destination, EIGRP looks for feasible successors in its topology table. If a feasible successor does exist, EIGRP begins using it immediately. If no feasible successors exist, EIGRP queries its neighbors.

For all the above to be accomplished, the components of EIGRP must provide:

Reliable transport mechanism
Neighbor discovery/recovery process, which allows EIGRP routers to discover and track other EIGRP speaking routers that are on directly connected networks; part of this process must be done reliably (guaranteed)
A way to discover which paths are loop free
A process to clear bad routes from the topology table of all routers on the network
A process for querying neighbors to find paths for lost destinations

Reliable Transport Protocol (可靠传输协议）
1.EIGRP updates and hellos are destined to the multicast address 224.0.0.10.

2.Protocol Number:88

EIGRP uses multiple packet types for reliable transport, all of which are identified by protocol number 88 in the IP header.

Hello packets are used to discover and recover neighbors. They are multicast and use unreliable delivery (no acknowledgment necessary).

Acknowledgments are used for reliable delivery and are always unicast.

Updates are used to convey route information. Updates are transmitted only when there is a change in the topology; they contain only the changed information, and they are sent only to routers that require the information. If only one router requires the update information, the updates are unicast; otherwise the updates are multicast. Updates use reliable delivery.

Queries and replies are used by DUAL. Queries can be multicast or unicast, and replies are always unicast. Queries and replies use reliable delivery.

Question: Fill in the blanks:
Each EIGRP neighbor receiving a ______ packet will ______ an acknowledgment.

a. unicast, broadcast

b. broadcast, unicast

c. multicast, unicast

d. unicast, multicast

When a router receives the hello packet from a new neighbor, EIGRP attempts to exchange routing updates with the neighbor. The updates contain all routes known by the sending routers and the metrics of those routes. When an EIGRP router receives updates from its neighbors, it builds a second table, the topology table, from which it builds a routing (forwarding) table. The topology table contains information needed to build a set of metrics and next hops to each reachable network, including:

Lowest bandwidth on the path to the destination
Total delay
Path reliability
Path loading
Minimum-path maximun transmission unit (MTU)
Feasible distance
Reported distance
Route source

Question: How can an EIGRP packet be identified by looking at the IP header? (choose all that apply)

a. Header will have User Datagram Protocol (UDP) Port 88

b. Header will have TCP Port 88

c. Header will have destination address of 224.0.0.10

d. Header will have IP protocol number 88

e. None of the above

五 13 2010

The dog that hasn’t missed a single riot for years

Posted by admin in 日记

Tags: 希腊, 狗 | 1 Comment

一条神奇的狗：2008年至今，希腊每一次民众抗议，闹事，照片中总会出现一条相同的狗

看来狗也会炒作呀。

There has been lots of riots and protests from both anarchists and workers in Athens, Greece specially the past few years. One interesting thing is that there is one dog that is spotted at these riots from 2008 till today

December 12. 2008

December 17. 2008 Read entire article.

五 12 2010

CCNP TSHOOT 642-832 Cert Kit: Video, Flash Card, and Quick Reference Preparation Package

Posted by admin in CISCO

Tags: 642-832, ccnp, Cert Kit, Flash Card, TSHOOT, Video | Add comment

CCNP TSHOOT 642-832 Cert Kit: Video, Flash Card, and Quick Reference Preparation Package | 2.08GB
Genre: eLearning

CCNP TSHOOT 642-832 Cert Kit is a best of breed late-stage preparation package that brings together three self-study tools into one value-priced package. The Network Troubleshooting Video Mentor contains 20 individual videos (with a total of about six hours of instruction) that demonstrate how to accomplish some of the most common troubleshooting tasks on Cisco routers and switches, and shows you how to verify that the network is working correctly. The CCNP TSHOOT Quick Reference provides you with detailed graphical-based information, highlighting only the key topics on the CCNP TSHOOT exam in cram-style format. This fact-filled Quick Reference allows you to get all-important information at a glance, helping focus on areas of weakness and enhance memory retention of important concepts. The CCNP TSHOOT Cert Flash Cards Online provide a concise review of all objectives on the CCNP TSHOOT 642-832 exam. This online exam preparation tool consists of a custom flash card application loaded with more than 300 total questions that test your skills and enhance retention of exam topics. The Flash Cards are available in both desktop and mobile formats.

# The Troubleshooting Video Mentor contains 20 individual videos for six hours of instruction
# The Cert Flash Cards Online provide 300 online flash cards for mobile and desktop devices
# The CCNP TSHOOT Quick Reference provides late stage review in print and PC formats

Table of Contents

Network Troubleshooting Video Mentor:
Lab 1: Spanning Tree Troubleshooting
Lab 2: Router Redundancy Troubleshooting
Lab 3: EIGRP Troubleshooting
Lab 4: OSPF Troubleshooting
Lab 5: Route Redistribution Troubleshooting
Lab 6: BGP Troubleshooting
Lab 7: IPv6 and OSPFv3 Troubleshooting
Lab 8: IPv6 and RIPng Troubleshooting
Lab 9: IOS Security Troubleshooting
Lab 10: DHCP Troubleshooting
Lab 11: NAT Troubleshooting
Lab 12: VoIP Troubleshooting
Lab 13: Multicast Troubleshooting
Lab 14: Troubleshooting Complex Environments

CCNP Tshoot Quick Reference:
I. Chapter One, Planning Network Maintenance
a. Maintenance Models and Methodologies
b. Maintenance Tools
c. Monitoring and Measurement Tools
d. Documenting Maintenance Processes
II. Chapter Two, Maintenance and Troubleshooting Tools
a. Using Command-line Tools
b. Using Specialized Tools
c. Using Special-Purchased Tools
III. Chapter Three, Creating a Troubleshooting Process
a. Evaluating Troubleshooting Methodologies
b. Establishing Baseline Metrics
c. Analyzing Network Problems
d. Seeking Problem Causes
e. Resolving Network Problems
f. Documentation
IV. Chapter Four, Maintaining and Troubleshooting Routing Protocols
a. IGPs
b. Route Redistribution
c. DHCP and NAT
d. WAN Connections
e. Network Performance
V. Chapter Five, Maintaining and Troubleshooting Campus Switching
a. InterVLAN Trunking
b. High Availability and Resiliency
c. Layer 3 Switches
d. Unified Communication
VI. Chapter Six, Maintaining and Troubleshooting Network Device Security
a. Attacks on Non-Hardened Devices
VII. Chapter Seven, Maintaining and Troubleshooting Applications and Services
a. WAAS
b. Virtualization
c. Storage
d. Load Balancing
VIII. Chapter Eight, Maintaining and Troubleshooting Remote User Networks
a. Security
b. Network Access and Authentication
c. VPNs
d. Branch Office Issues

CCNP Tshoot Cert Flash Cards Online:
1. Planning Maintenance for Complex Networks
2. Selecting Maintenance and Troubleshooting Tools and Applications
3. Planning Troubleshooting Processes for Complex Enterprise Networks
4. Maintaining and Troubleshooting Campus Switching Based Solutions
5. Maintaining and Troubleshooting Routing Based Solutions
6. Maintaining and Troubleshooting Network Security Solutions
7. Maintaining and Troubleshooting Integrated, Complex Enterprise Networks

INSTALLATION
Unpack, burn or mount, enjoy.

Homepage: http://www.ciscopress.com/bookstore/product.asp?isbn=1587141205
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五 12 2010

Cisco Press CCNP SWITCH 642-813 Cert Kit DVD

Posted by admin in CISCO

Tags: 2.4 GB, 642-813, ccnp, Cert Kit DVD, Cisco Press, iso, switch | Add comment

Cisco Press CCNP SWITCH 642-813 Cert Kit DVD | ISO | 2.4 GB

CCNP SWITCH 642-813 Cert Kit is a best of breed late-stage preparation package that combines three self-study tools into one value-priced package. This product provides you with over 6 hours of personal instruction from Sr. instructor Dave Hucaby on the LAN Switching Video Mentor, a concise review of CCNP SWITCH exam topics in the CCNP SWITCH Quick Reference, and 300 exam review questions in both desktop and mobile formats in the CCNP SWITCH Cert Flash Cards Online.
LAN Switching Video Mentor is a DVD video product. The DVD contains a series of short instructional videos that demonstrate how to accomplish some of the most common configuration and troubleshooting tasks on the Catalyst platforms and how to verify that the network is working correctly. The DVD contains 20 individual videos for a total of about six hours of instruction. CCNP SWITCH Quick Reference provides you with detailed, graphical-based information, highlighting only the key topics on the CCNP SWITCH exam in cram-style format. This fact-filled Quick Reference allows you to get all-important information at a glance, helping focus on areas of weakness and enhance memory retention of important concepts.

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无色无味(杨波) 的Web Log(博客)

Teredo Components

Simware 使用指南

好吧。我承认你赢了。

我受够了具有中国特色的互联网了。

cache test

About Cisco EIGRP（二）