Mr. Mturi Elias University Computing Centre SYSTEMS ADMIN TRAINING WORKSHOP

Mr. Mturi Elias 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 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 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 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 Testing Your NIC Viewing Your Activated Interfaces  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 Testing Your NIC (2) Testing Link Status from the Command Line.  Link Status Output from mii-tool 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 Testing Your NIC (3) Testing Link Status from the Command Line. Link Status Output from ethtool 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 Testing Your NIC (4) Viewing NIC Errors  ifconfig  ethtool –S eth0

Mr. Mturi Elias 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 Testing Your Network Connectivity (2) Using Ping To Test Connectivity  A lack of response could be due to: 1. A server with that IP address doesn't exist 2. The server has been configured not to respond to pings 3. A firewall or router along the network path is blocking ICMP traffic 4. You have incorrect routing. 5. Either the source or destination device having an incorrect IP address or subnet mask.

Mr. Mturi Elias Testing Your Network Connectivity (3) Using Ping To Test Connectivity root]# ping -c 2 PING websvr.udsm.ac.tz ( ) 56(84) bytes of data. 64 bytes from websvr.udsm.ac.tz ( ): icmp_seq=0 ttl=254 time=0.588 ms 64 bytes from websvr.udsm.ac.tz ( ): icmp_seq=1 ttl=254 time=0.470 ms --- websvr.udsm.ac.tz ping statistics 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 Testing Your Network Connectivity (4) You may get a "Destination Host Unreachable" message. There are a number of reasons for this: 1. The server might be down, or disconnected for the network. 2. Your NIC might not have the correct duplex settings; you may verify this with the mii-tool command. 3. You might have the incorrect type of cable connecting your Linux box to the network. 4. In the case of a wireless network, your SSID or encryption keys might be incorrect.

Mr. Mturi Elias Testing Your Network Connectivity (5) Using netstat Command to test the connections : 1. Displays network connections, routing tables, interface statistics, masquerade connections, netlink messages, and multicast memberships. 2. Can be used to check for open ports, an important security issue.

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

Mr. Mturi Elias 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 Testing Your Network Connectivity (8) root]# traceroute traceroute to ( ), 30 hops max, 38 byte packets ( ) ms ms ms ( ) ms ms ms ( ) ms ms ms ( ) ms ms ms c 5 fus-rt002-LANB.core.globalconnex.net ( ) ms ms ms cc ( ) mscc msc ms

Mr. Mturi Elias 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 Testing Your Network Connectivity (6)

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

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

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

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

Mr. Mturi Elias 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

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

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 Ethereal (Continued)

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

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

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

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Conclusion Lest Know When You Have Problem You Need To Be Proactive.