Cisco^® CCNP Support : Troubleshooting, Connection Oriented And Connectionless Protocols, Tcp/ip, Router Performance.

Exam cram

1.0 The recommended sequence of steps for systematic troubleshooting are:

Step A: Define the Problem - Here you define the problem by stating the problem symptoms and associated causes.

Step B: Gather Facts - Fact gathering helps in isolating problem areas. Fact gathering is done by questioning the affected users, administrators, and using tools such as protocol analyzers.

Step C: Consider the Possibilities - The objective here is to narrow down the possible causes. Use the facts gathered in Step B and narrow down the possible causes by systematic reasoning and diagnostic methods.

Step D: Create Action Plan - Based on the narrowed down possibilities, create an action plan to troubleshoot the problem.

Step E: Implement Action Plan - Here you implement the Action Plan. Make sure the steps are documented, so that you can retract if the action plan does not give intended results.

Step F: Observe the Results - Check if the actions that have been implemented yielded desired results. If not, don't forget to undo earlier changes that did not work.

Step G: Repeat the Problem Solving Process - This step is required if the Action Plan did not work. You need to get closer to the actual problem with each iteration.

Step H: Document Facts - The final stage of problem solving model is to document the process. Though it is the final step, note that documentation at every step facilitates easy documentation after the problem is resolved.

2.0 Connectionless and Connection Oriented Protocols:

2.1 The following are examples of connectionless protocols:
1. IP (Internet Protocol) - IP is the network-layer connectionless protocol of TCP/IP suite.
2. UDP (User Datagram Protocol)- UDP is a connectionless transport layer protocol of TCP/IP suite.
3. Novell IPX
4. AppleTalk DDP (Datagram Delivery Protocol)
5. CLNP (Connectionless Network Service) used by DECnet

2.2 The following are examples of connection oriented protocols:
1. TCP
2. Novell SPX
3. ATM
4. X.25
5. ATP ( AppleTalk Protocol) - an Apple Talk transport layer protocol.

3.0 Token Ring:

Beaconing is used in Token Ring networks to detect and try to rectify certain network faults. By the process of Beaconing, the Token Ring network try to reconfigure by eliminating the faulty network region.

In general, network faults can be grouped into hard errors, and soft errors. 
Hard errors are the those that are permanent and can not be recovered by software routines. Examples of hard errors are cable cuts and station hardware failures. 
On the other hand, soft errors temporarily disrupt the network services and can be recovered by software routines.

There are two types of soft errors that are tracked by Token Ring networks:

1. Isolating faults - Isolating faults are limited to a particular fault domain. The fault domain is usually a node and its NAUN. Examples of isolating errors are: Line errors, burst errors, and internal errors.

2. Non Isolating faults- Non isolating faults are not limited to a particular fault domain. The error is likely to be spread all over the ring, like congestion. Examples of non isolating faults are: Lost frame, Token, Frequency, and congestion errors.

FDDI:

The following are the important characteristics of FDDI:

1. FDDI uses 100Mbps, dual-ring LAN and uses Token passing (Token passing mechanism is similar to Token Ring, however remember that Token Ring networks has a speed of 4 or 16 Mbps only).

2. FDDI uses fiber as the medium of transmission. Two types of fibers exist: single mode, and multi mode fibers. Single mode fiber allows much higher bandwidths and longer cable lengths compared to multi mode fiber. However, multi mode fibers are cheaper.

3. Improved security due to fiber transmission medium. It is very difficult to tap fiber transmission without being detected.

4.0 TCP/IP

4.1 TCP/IP based applications and their protocols are as described below:

1. Electronic Mail uses SMTP (Simple Mail Transfer Protocol).
2. Network Management applications use SNMP
3. Telnet uses terminal emulation
4. Distributed file services use NFS (Network File System)

4.2 Ping and Trace

During the process of network troubleshooting, you will be required to know the host or network reachability at several points of troubleshooting process. The two commands are extremely useful to check the host reachability and the path that is taken to reach the destination are 'ping' and 'trace' commands. 

'Ping' command can be used to check the connectivity on AppleTalk, CLNS, Novell, and various other protocols. To perform an extended ping, simply give 'ping' at the command prompt. You will be prompted for other parameters like protocol, target IP address, etc.

The following are the possible responses for an IP ping command:
! - indicates that a reply is received
. - indicates that the router has timed out.
U - indicates that the destination is unreachable
N - indicates that the network is unreachable
P - indicates that the protocol is unreachable
? - indicates unknown packet type
Q - indicates source quench

'trace' command can be used to see the route that a packet takes to reach the destination. The trace command discovers the path taken to reach its final destination by sending out probe datagrams. The first datagram is sent out with a TTL (Time To Live) value of just 1. This causes the first router to discard the packet and send back 'time exceeded' message. Thus the first router enroute is discovered! Then, the TTL is incremented by 1 (now TTL is 2) and the datagram is sent out again. Now the second router enroute discards the packet as the TTL reached zero, and sends back 'time exceeded' message to the source. This process is repeated till the destination is reached. By doing so, the exact path that a packet takes to reach the destination is established.

TCP/IP troubleshooting:

The first step in troubleshooting TCP/IP problems is to start with the local host. You can ping the local host (use ping 127.0.0.1, a successful ping ensures that the TCP/IP stack is installed properly) and if you are successful, proceed one step at a time. The next step would be to ping the gateway or the next hop address. This procedure can be followed until you reach the destination network. Once you establish basic IP connectivity, perform any troubleshooting for higher layer protocols such as DNS resolution, FTP, or Telnet. Though it may sometimes be faster to trace route to the destination and find the problem route, it may not always be successful. It is recommended to start at the source and proceed one step at a time towards the destination network.

5.0 Router Performance:

The following are the features that affect performance on routers:
1. Queuing
2. Random Early Detection 
3. Compression
4. Filtering
5. Encryption
6. Accounting

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