LSNDI RMRA 1 Design and troubleshooting M Clements

LSNDI RMRA 2 Introduction Need for troubleshooting Troubleshooting tools Examples Lab work

LSNDI RMRA 3 Broken routing configs Configurations can sometimes fail to work as the writer hoped Incorrect addressing (common) Incorrect configuration of parameters Missing commands Misunderstanding of the IOS

LSNDI RMRA 4 Problem Manifestation Routes/ hosts cannot be reached Routers or switches slow in operation ACLs fail to work Routing fails Failover systems fail to work as hoped Parts of network fine, others not Etc. etc.

LSNDI RMRA 5 Tools to help diagnose problems Ping – runs on routers and hosts Extended ping – runs on routers and switches only Traceroute/ tracert Debug tools Show tools

LSNDI RMRA 6 ping Echo request 1 The echo request is an ICMP message whose data is expected to be received back in an echo reply. The host must respond to all echo requests with an echo reply containing the exact data received in the request message.ICMP Type must be set to 8. Code must be set to 0. The Identifier and Sequence Number can be used by the client to match the reply with the request that caused the reply. The data received by the Echo Request must be entirely included in the Echo Reply.

LSNDI RMRA 7 1 ping Echo reply The echo reply is an ICMP message generated in response to an echo request, and is mandatory for all hosts and routers. Type and code must be set to 0. The identifier and sequence number can be used by the client to determine which echo requests are associated with the echo replies. The data received in the echo request must be entirely included in the echo reply.

LSNDI RMRA 8 For you to try Open traffic sniffer e.g. Ethereal or Wireshark Optionally you can set up a filter for ping traffic (in and out) Start Ethereal or wireshark Ping an IP address you know is ‘up’ with cmd Wait until the ping completes Stop the sniffer Examine the icmp traffic

LSNDI RMRA 9 Questions What was the payload? How many packets were sent? How many were received? What was the time between ping packets being sent? What is the sequence number in a request and its subsequent reply?

LSNDI RMRA 10 Extended ping Implemented on routers and switches Allows more complex parameters Can send ping from a specific interface Can change data size and pattern Can validate replies Can change number of times ping is sent Can set other parameters too

LSNDI RMRA 11 Extended ping ATL#ping Protocol [ip]: Target IP address: Repeat count [5]: Datagram size [100]: Timeout in seconds [2]: Extended commands [n]: y Source address or interface: Type of service [0]: Set DF bit in IP header? [no]: Validate reply data? [no]: Data pattern [0xABCD]: Loose, Strict, Record, Timestamp, Verbose[none]: Sweep range of sizes [n]: Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to , timeout is 2 seconds: Packet sent with a source address of !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 20/32/48 ms

LSNDI RMRA 12 For you to try Open Packet Tracer (4.1 minimum) Connect 2 routers with a serial connection Set up addresses for the serial interfaces Choose DCE and set clock rate Turn the interfaces on Try the extended ping command – type ping [enter] Write down the parameters that you could change

LSNDI RMRA 13 Traceroute/ tracert This uses a set of pings to show routers between source and destination Useful to see how traffic crosses a network Shows ping time, IP addresses and names where available

LSNDI RMRA 14 Example of the use of tracert C:\Documents and Settings\luther>tracert Tracing route to [ ] over a maximum of 30 hops: 1 1 ms <1 ms <1 ms ms 9 ms 9 ms ms 13 ms 10 ms ms 277 ms 234 ms pc bn.blueyonder.co.uk [ ] 5 11 ms 13 ms 10 ms pc bn.blueyonder.co.uk [ ] 6 27 ms 18 ms 13 ms ms 11 ms 11 ms bbc-gw0-linx.prt0.rbsov.bbc.co.uk [ ] ms 14 ms 12 ms ms 13 ms 11 ms fe0-0.rt0-frontpost.prodgw.bbc.co.uk [ ] ms 15 ms 12 ms www1.cwwtf.bbc.co.uk [ ] Trace complete.

LSNDI RMRA 15 Traceroute on a router Full command traceroute can be used here – (Rather than tracert 8.3 dos convention) Shows *NIX heritage Performs the same as tracert.exe on the host PC

LSNDI RMRA 16 For you to try Open a packet sniffer Start the sniffer for the PC’s network interface Use cmd to invoke a tracert to a known host Capture the network dialogue Stop the sniffer Examine the dialogue

LSNDI RMRA 17 Questions What type of protocol is used for the tracert? Examine the ‘time to live’ flag in Internet Protocol Look at each ping request separately What is different about the time to live? Now see which host replied to that request – hint - the sequence number allows this How do you think the tracert works now that you have examined this traffic?

LSNDI RMRA 18 Debug tools debug command runs on routers and switches Allow us to see various dynamic parameters in real time – e.g. arrival of routing information Use with care – takes router processing power – always turn off after use Type router#debug ? To see the options available

LSNDI RMRA 19 For you to try At the router Priv Exec prompt type debug ? Write down the command options displayed Now follow the ip option Add the ? Write down all options you can see These commands are all related to routing and will help to diagnose routing problems

LSNDI RMRA 20 Show commands Typing show at the Priv exec prompt allows us to see static information about the router E.g. routing table, interface information, clock, access-lists etc Make a list of the show options available in Packet Tracer

LSNDI RMRA 21 You, the detective These tools allow a wide range of tests to be made You need to devise tests to develop a hypothesis that fits your network problem You may need to devise a test plan and eliminate items one at a time A good diagram is ESSENTIAL when troubleshooting

LSNDI RMRA 22 LAB work Open Troubleshoot.pkt from this week’s web menu Open the document TroubleshootingConnectivity_Handout.doc Work through the example

LSNDI RMRA 23 References 1