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SYSTEMS ADMIN TRAINING WORKSHOP

SYSTEMS ADMIN TRAINING WORKSHOP. University Computing Centre. Overview. Introduction Doing Basic Cable and Link Tests Testing Your NIC Testing Network Connectivity Detecting Network Congestion Packet Capturing Basic DNS Troubleshooting. Introduction. Two Network related problems

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SYSTEMS ADMIN TRAINING WORKSHOP

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  1. SYSTEMS ADMIN TRAINING WORKSHOP University Computing Centre Mr. Mturi Elias

  2. Overview • Introduction • Doing Basic Cable and Link Tests • Testing Your NIC • Testing Network Connectivity • Detecting Network Congestion • Packet Capturing • Basic DNS Troubleshooting Mr. Mturi Elias

  3. Introduction • Two Network related problems • Network Slowness • Lack of Connectivity • Sources of Network Slowness • NIC duplex and speed incompatibilities • Network congestion • Poor routing • Bad cabling • Electrical interference Mr. Mturi Elias

  4. Introduction • Sources of Network Slowness • An overloaded server at the remote end of the connection • Misconfigured DNS . • Sources of a Lack of Connectivity • The cables are bad. • The switch or router to which the server is connected is powered down. • The cables aren't plugged in properly. • The remote server or an application on the remote server being shut down. Mr. Mturi Elias

  5. Doing Basic Cable and Link Tests • NIC’s “link” light is on: indicates the link is functioning properly. • In most cases a lack of link is due to the wrong cable type being used. • There are two types of Ethernet cables crossover and straight-through. • Always make sure you are using the correct type. Mr. Mturi Elias

  6. Testing Your NIC • Viewing Your Activated Interfaces • [root@rdu root]# ifconfig • Viewing All Interfaces • The ifconfig -a command provides all the network interfaces, whether they are functional or not. • Testing Link Status from the Command Line. • Both the mii-tool and ethtool commands command will provide reports on the link status and duplex settings for supported NIC Mr. Mturi Elias

  7. Testing Your NIC (2) • Testing Link Status from the Command Line. • Link Status Output from mii-tool [root@rdu root]# mii-tool -v eth0: negotiated 100baseTx-FD, link ok product info: vendor 00:08:18, model 25 rev 0 basic mode: autonegotiation enabled basic status: autonegotiation complete, link ok capabilities: 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD advertising: 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD flow-control link partner: 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD eth1: no link product info: vendor 00:08:18, model 25 rev 0 basic mode: autonegotiation enabled basic status: no link capabilities: 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD advertising: 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD flow-control Mr. Mturi Elias

  8. Testing Your NIC (3) • Testing Link Status from the Command Line. • Link Status Output from ethtool [root@rdu root]# ethtool eth0 Settings for eth0: Supported ports: [ TP ] Supported link modes: 10baseT/Half 10baseT/Full 100baseT/Half 100baseT/Full 1000baseT/Half 1000baseT/Full Supports auto-negotiation: Yes Advertised link modes: 10baseT/Half 10baseT/Full 100baseT/Half 100baseT/Full 1000baseT/Half 1000baseT/Full Advertised auto-negotiation: Yes Speed: 1000Mb/s Duplex: Full Port: Twisted Pair PHYAD: 0 Transceiver: internal Auto-negotiation: on Supports Wake-on: g Wake-on: d Link detected: yes Mr. Mturi Elias

  9. Testing Your NIC (4) • Viewing NIC Errors • ifconfig • ethtool –S eth0 Mr. Mturi Elias

  10. Testing Your Network Connectivity • Using Ping To Test Connectivity • ping sends ICMP echo packets that request a corresponding ICMP echo-reply response from the device at the target address. • Because most servers will respond to a ping query it becomes a very handy tool. Mr. Mturi Elias

  11. Testing Your Network Connectivity (2) • Using Ping To Test Connectivity • A lack of response could be due to: • A server with that IP address doesn't exist • The server has been configured not to respond to pings • A firewall or router along the network path is blocking ICMP traffic • You have incorrect routing. • Either the source or destination device having an incorrect IP address or subnet mask. Mr. Mturi Elias

  12. Testing Your Network Connectivity (3) • Using Ping To Test Connectivity • [root@rdu root]# ping -c 2 www.udsm.ac.tz • PING websvr.udsm.ac.tz (196.44.161.110) 56(84) bytes of data. • 64 bytes from websvr.udsm.ac.tz (196.44.161.110): icmp_seq=0 ttl=254 time=0.588 ms • 64 bytes from websvr.udsm.ac.tz (196.44.161.110): icmp_seq=1 ttl=254 time=0.470 ms • --- websvr.udsm.ac.tz ping statistics --- • 2 packets transmitted, 2 received, 0% packet loss, time 1007ms • rtt min/avg/max/mdev = 0.470/0.529/0.588/0.059 ms, pipe 2 Mr. Mturi Elias

  13. Testing Your Network Connectivity (4) • You may get a "Destination Host Unreachable" message. There are a number of reasons for this: • The server might be down, or disconnected for the network. • Your NIC might not have the correct duplex settings; you may verify this with the mii-tool command. • You might have the incorrect type of cable connecting your Linux box to the network. • In the case of a wireless network, your SSID or encryption keys might be incorrect. Mr. Mturi Elias

  14. Testing Your Network Connectivity (5) • Using netstat Command to test the connections: • Displays network connections, routing tables, interface statistics, masquerade connections, netlink messages, and multicast memberships. • Can be used to check for open ports, an important security issue. Mr. Mturi Elias

  15. Testing Your Network Connectivity (6) • Using netstat Command to test the connections: [root@rdu root]# netstat -an Active Internet connections (servers and established) Proto Recv-Q Send-Q Local Address Foreign Address State tcp 0 0 0.0.0.0:32768 0.0.0.0:* LISTEN tcp 0 0 127.0.0.1:32769 0.0.0.0:* LISTEN Mr. Mturi Elias

  16. Testing Your Network Connectivity (7) • Using traceroute to Test Connectivity • Prints the route packets take to get to a particular network host. • This helps you verify that routing over the networks in between is correct. • Uses UDP packets by default. Mr. Mturi Elias

  17. Testing Your Network Connectivity (8) [root@rdu root]# traceroute www.yahoo.com traceroute to www.yahoo-ht2.akadns.net (209.73.186.238), 30 hops max, 38 byte packets 1 82.206.143.66 (82.206.143.66) 0.802 ms 0.729 ms 0.677 ms 2 10.103.160.1 (10.103.160.1) 1.393 ms 1.713 ms 1.213 ms 3 172.17.7.7 (172.17.7.7) 533.409 ms 520.447 ms 786.705 ms 4 172.17.7.17 (172.17.7.17) 576.658 ms 519.385 ms 515.692 ms c 5 fus-rt002-LANB.core.globalconnex.net (80.255.48.2) 523.617 ms 519.992 ms 514.423 ms cc 6 80.255.35.162 (80.255.35.162) 624.555 mscc 624.800 msc 626.754 ms Mr. Mturi Elias

  18. Testing Your Network Congention • Using MTR To Detect Network Congestion • Matt's Traceoute is an application you can use to do a repeated traceroute in real time. • It dynamically shows the round-trip time to reach each hop along the traceroute path. • The constant updates enable you not only to visually determine which hops are slow and when are they slow. Mr. Mturi Elias

  19. Testing Your Network Connectivity (6) Mr. Mturi Elias

  20. PACKET CAPTURING • Sniffer, tcpdump, Ethereal, ntop Mr. Mturi Elias

  21. What is Packet Capture? • Real time collection of data as it travels over networks • Tools called: • packet sniffers • packet analysers • protocol analysers, and sometimes even • traffic monitors Mr. Mturi Elias

  22. When Packet Capture? • Most powerful technique • When need to see what client and server are actually saying to each other • When need to analyse type of traffic on network • Requires understanding of network protocols to use effectively Mr. Mturi Elias

  23. How to use tcpdump • Can just type its name (as root): $ tcpdump • ...but get a huge amount of data! • Can restrict the data collected using a filter • A filter may select addresses, protocols, port numbers,... Mr. Mturi Elias

  24. tcpdump: some options • -c n — capture a count of n packets then stop • -w file — write raw data to file. • Very useful — can filter and analyse this later with tcpdump, ethereal or other tools • but you cannot see what you are capturing till later! • -i interface — collect from interface instead of lowest numbered network interface • -s bytes — collect no more than bytes of data from each packet instead of default 68 bytes • -e — show link level info, e.g., Ethernet addresses • -x — gives a hexadecimal dump of packets • excluding link level data • -X— display ASCII as well as hexadecimal if have –x option too • Many more options: man tcpdump Mr. Mturi Elias

  25. tcpdump Filters: host and port • Show all network traffic to and from 192.168.0.1: tcpdump host 192.168.0.1 • Show packets to 192.168.0.1: tcpdump dst 192.168.0.1 • Show packets to port 68 on 192.168.0.1: tcpdump dst 192.168.0.1 and port 68 Mr. Mturi Elias

  26. tcpdump filters: networks • Capture traffic to or from 205.153.60/24: tcpdump net 172.19.64/18 • can specify network as source or destination: tcpdump src net 205.153.60/24 tcpdump dst net 172.19.64/18 Mr. Mturi Elias

  27. tcpdump filters: protocol • tcpdump ip • tcpdump tcp • tcpdump ip proto ospf • This will catch DNS name lookups, but not zone transfers (which use tcp): • tcpdump udp port 53 Mr. Mturi Elias

  28. Ethereal King of the Packet Analysers! Available for Linux, Unix, Windows Mr. Mturi Elias

  29. Ethereal • Ethereal can read data captured by tcpdump, e.g., $ ethereal –r tcpdump.pcap • or File -> Open • Can capture data itself • Uses same filter language as tcpdump Mr. Mturi Elias

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  32. You can expand any protocol: • If we click on the + next to Bootstrap Protocol, we can see the details of the DHCP Request: Mr. Mturi Elias

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  34. Ethereal (Continued) • Text based ethereal called tethereal: • If you machine does not have GUI or you are using a remote server/computer tethereal is the best for you. • Just type tethereal in your command prompt Mr. Mturi Elias

  35. Ethereal (Continued) Mr. Mturi Elias

  36. Basic DNS Troubleshooting • Sometimes the source of problems can be due to misconfigured DNS rather than poor network connectivity. • DNS is the system that helps map an IP address to your Web site's domain name and your site may suddenly become unavailable if the mapping is incorrect Mr. Mturi Elias

  37. Basic DNS Troubleshooting (2) • Using nslookup to Test DNS • The nslookup command can be used to get the associated IP address for your domain and vice versa. Mr. Mturi Elias

  38. Basic DNS Troubleshooting (3) • Using nslookup To Check Your IP Address Mr. Mturi Elias

  39. Basic DNS Troubleshooting • Using the host Command to Test DNS Mr. Mturi Elias

  40. Basic DNS Troubleshooting • Using the dig Command to Test DNS Mr. Mturi Elias

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  42. Conclusion Lest Know When You Have Problem You Need To Be Proactive. Mr. Mturi Elias

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