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Network Configuration An Introductory Tutorial. Network Parameters The following are common parameters that need to be set in a networked computer: DNS.

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Presentation on theme: "Network Configuration An Introductory Tutorial. Network Parameters The following are common parameters that need to be set in a networked computer: DNS."— Presentation transcript:

1 Network Configuration An Introductory Tutorial

2 Network Parameters The following are common parameters that need to be set in a networked computer: DNS Servers (e.g ) The logical (e.g. IP) address of the DNS servers to be used to resolve domain names These can be local (e.g. frankie.csfac8.uwindsor.ca) or remote (e.g. Host and domain information This includes the computer’s name (e.g. elvis) and the domain on which it resides (e.g. csfac8.uwindsor.ca)

3 Network Parameters Logical address (e.g. IP address: ) This address is required to participate on a WAN, such as the Internet Subnet mask (e.g ) This is the binary mask that should be used to extract the network and subnet information from the host’s address Default gateway (e.g ) This is the logical (e.g. IP) address of the router which should receive the host’s Internet-bound packets All of these values would be given to a computer’s user by a network administrator

4 DNS Servers DNS servers use the DNS protocol to determine the logical (e.g. IP) address of a host, given its domain name e.g Many servers are given (in a specific order) so that local DNS servers are first This is because the main DNS servers (Internic) would not know local domain names e.g. An Internic server would know about uwindsor.ca, but not frankie.csfac8.uwindsor.ca) These server addresses would usually be well- known

5 Host and Domain Info Host name: This is the name of the host on the network e.g. elvis Domain name: This is the name of the domain on which the host resides A domain is a named group of computers, which may correspond to a subnet of addresses e.g. csfac8.uwindsor.ca refers to the LAN on the 8 th floor of Lambton Tower Given these two pieces of information, the host’s DNS name would be elvis.csfac8.uwindsor.ca Depending on the operating system, the domain may require that you log on first The network admin will create one or more domains, but each host’s user can determine the host name, provided it is unique

6 Logical Address This is typically an IP address This address is necessary for all WAN (including Internet) communication Routing uses the logical address for finding the path for packets These addresses are normally assigned automatically by a DHCP/BOOTP server They can be random addresses on the network, or sequentially assigned

7 Subnet Mask The subnet mask that it used by the host is the same subnet mask used by the nearest routers e.g. If using 2-level subnetting of 2 and 3 bits, this mask would be the last subnet mask used ( ) A network admin would know the subnet masks he/she assigned to each network

8 Default Gateway The default gateway (router) is the router to which all Internet-bound traffic should be sent Typically, a LAN will have exactly one router, and this will be its address If there is more than one router, and only one leads to the Internet, the Internet-connected router’s address is used here If there is more than one router that connects to the Internet, either address could be used The network admin would know the address of the routers

9 Troubleshooting Networks How to Determine Network Configuration or Hardware Problems

10 Troubleshooting A network admin’s job is not just to set up a network, but maintain it Thus, if anything goes wrong, the admin should track down the problem somehow The problem may be a configuration error, which the admin should fix The problem may be a hardware failure, which can only be fixed by repairing or replacing the hardware Nevertheless, the admin must determine which hardware has failed, so this can happen

11 A Typical Scenario A user calls up the network admin, saying their network connection is down For most non-technical users, even this clear of a statement of the problem might not be possible A network admin will eventually figure at least this much out from the user’s comments

12 Step 1: Test Local Connectivity First, an admin will try to connect to a local computer cmd% ping frankie.csfac8.uwindsor.ca ping: unknown host frankie.csfac8.uwindsor.ca This could mean DNS servers are unavailable The admin should check the DNS server addresses, and the servers Next, the admin will make sure the IP address works cmd% ping Destination host unreachable. This could mean no connectivity The admin should check the configuration settings (ipconfig, netconfig, network- admin) However, if the ping command responds from a router that a host is unreachable, the node may actually be unreachable, or the address may not be bound Obviously, we have connectivity since the router sent a message to us

13 How Ping Works Ping works by sending an ICMP Echo Reqest to the destination The destination sends back an ICMP Echo Reply to the host The host records the round trip time, and repeats the process a few times

14 A Problem With Ping ICMP Echo Requests are often disabled in some networks This is due to denial of service attacks that use ICMP Echo Request/Reply In these networks, ping will not work

15 Check Configuration Settings In Windows (2000/XP): C:\> ipconfig (success) Windows IP Configuration Ethernet adapter Wireless Network Connection: Connection-specific DNS Suffix. : csfac8.uwindsor.ca IP Address : Subnet Mask : Default Gateway : (failure) Windows IP Configuration Ethernet adapter Wireless Network Connection: Media State : Media disconnected

16 Edit Configuration Settings In Windows (2000/XP), editing your network configuration settings can be done from TCP/IP properties Open control panel, select Network Connections Select your connection, click Properties Select Internet Protocol (TCP/IP), click Properties From here you can edit your configuration settings manually, or specify that a DHCP should provide the values for you

17 Check/Edit Configuration Settings In Linux: Linux% network-admin In Solaris: Solaris% netconfig These bring up a graphical dialog where configuration can be viewed and edited

18 Step 2: Test Remote Connectivity First, an admin will try to connect to a local computer cmd% ping ping: unknown host This could be a routing problem Most likely the routing problem is within the organization The network administrator should check the route using the traceroute (traceroute, tracert) command

19 Testing Routes The traceroute command can give the logical addresses of each router in a route It may also tell you if there is a problem with the route In Windows (2000/XP): tracert In Linux/Solaris: traceroute

20 Windows Tracert Output C:\>tracert Tracing route to [ ] over a maximum of 30 hops: 1 1 ms 1 ms 1 ms ms 16 ms 20 ms ms 13 ms 13 ms d home.cgocable.net [ ] 4 30 ms 15 ms 18 ms cgowave cgocable.net [ ] 5 30 ms 17 ms 17 ms cgowave cgocable.net [ ] 6 29 ms 18 ms 17 ms gw-google.torontointernetxchange.net [ ] 7 19 ms 37 ms 17 ms ms 23 ms 31 ms ms 40 ms * ms 92 ms 86 ms ms 89 ms 94 ms ms 95 ms 90 ms ms 98 ms 89 ms ms 94 ms 88 ms Trace complete.

21 Windows Tracert Output The output contains lines like the following: 5 30 ms 17 ms 17 ms cgowave cgocable.net [ ] 5: The 5 th hop 30,17,17ms: Round trip times to/from the router cgowave cgocable.net [ ]: The domain name and address of the router

22 Linux traceroute Output $ traceroute traceroute: Warning: has multiple addresses; using traceroute to ( ), 30 hops max, 38 byte packets 1 ssr68 ( ) ms ms ms 2 ssr ( ) ms ms ms 3 cs-ssr-main.newcs.uwindsor.ca ( ) ms ms ms 4 passport1.uwindsor.ca ( ) ms ms ms 5 internet.uwindsor.ca ( ) ms ms ms 6 acs7204.uwindsor.ca ( ) ms ms ms 7 f0-1.na03.b yyz01.atlas.cogentco.com ( ) ms ms ms 8 g9-1.core01.yyz02.atlas.cogentco.com ( ) ms ms ms 9 p15-0.core01.yyz01.atlas.cogentco.com ( ) ms ms ms 10 p13-0.core02.ord01.atlas.cogentco.com ( ) ms ms ms 11 p15-0.core01.ord01.atlas.cogentco.com ( ) ms ms ms 12 p6-0.core01.ord03.atlas.cogentco.com ( ) ms ms ms 13 google.ord03.atlas.cogentco.com ( ) ms ms ms ( ) ms ms ( ) ms ( ) ms ( ) ms ( ) ms ( ) ms ms ms

23 How To Interpret the Output The round trip times can tell you if there is a problem A round trip time of * means a timeout has occurred, which is a definite problem A round trip time > 500 ms usually means there is a problem with that router The router could be dropping packets (due to overloaded buffer or routing loops typically)

24 How Does Traceroute Work? Traceroute sends either a UDP or ICMP Echo packet to the destination Initially, the hop limit is set to 1, which causes the first router to drop the packet Routers, however, will respond with an ICMP Time Exceeded error message, which contains the router’s IP address The process is repeated a few times to get a few round trip times The domain name of the IP address is found (for convenience of the network admin) Next, the process is repeated with a hop limit of 2 Then 3, 4, etc. until the destination host is reached

25 A Problem with Traceroute One problem with traceroute is that it could read a false path If the routers reconfigure (e.g. due to congestion) during its execution, the readings could be inaccurate S A1A2 D B2

26 A Problem with Traceroute One problem with traceroute is that it could read a false path If the routers reconfigure (e.g. due to congestion) during its execution, the readings could be inaccurate S A1A2 D B2 1A1

27 A Problem with Traceroute One problem with traceroute is that it could read a false path If the routers reconfigure (e.g. due to congestion) during its execution, the readings could be inaccurate S A1A2 D B2 1A1 2A2

28 A Problem with Traceroute One problem with traceroute is that it could read a false path If the routers reconfigure (e.g. due to congestion) during its execution, the readings could be inaccurate S A1A2 D B2 1A1 2A2 3D

29 A Problem with Traceroute For networks with ICMP Echo Request/Reply disabled, the UDP format must be used Some traceroute commands do not support the UDP message format, however

30 LAN Setup 10BaseT Ethernet g Wireless

31 10BaseT Ethernet Setup To connect a 10BaseT Ethernet network: Install a network interface card (NIC) into each computer (host) Connect each NIC to a hub or switch, using unshielded twisted pair (UTP) cabling Hub: Every frame received by a hub is reproduced on all of it’s ports Switch (or Cable/DSL Router): Every frame received by a switch is examined, and the correct port is determined for the frame A Cable/DSL also provides network address translation (NAT)

32 802.11g Wireless Setup To setup a g wireless network: Install an g (or b) NIC into each host Plug a wireless router or base station into your Internet connection (e.g. cable modem) Configure the SSID and security protocols on the wireless router and each of the NICs e.g. WPA encryption, and specify the key

33 Ad Hoc Wireless Networks If you have only a few hosts (2-3), you can create an ad hoc network This type of network does not have a base station (or wireless router) The hosts communicate directly with one another

34 Wireless Networks Comment A wireless network connection is often not useful for a desktop PC For this reason, wireless routers typically contain a few Ethernet ports It is typical to have desktop PCs wired, and notebooks and PDAs will have wireless e.g. Notebooks with g and PDAs with b Wireless networks will be discussed in depth later

35 Packet Sniffers Packet sniffers are a useful tool for exploration of networking They can also be used by network programmers to diagnose packet format errors They typically examine many protocols This includes the header information e.g. Wireless, Ethernet, TCP/IP, HTTP Some common packet sniffers are: Ethereal (Linux/Mac/Windows, multi-protocol) TCPDump (Linux/Windows, TCP/IP) Kismet (Linux, wireless)

36 Ethereal Tutorial Here is how to sniff packets using Ethereal: Start Ethereal Select the correct network interface Start capturing packets, stop when done Select a packet from the list Examine the packet hierarchy and header information, such as: Ethernet or wireless frame headers IP datagram headers TCP datagram headers SMTP message


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