Chapter 1. 6 – Troubleshooting TCP/IPPublished: February 2. A network administrator must know how to methodically analyze a TCP/IP- related networking problem in terms of the various layers of the TCP/IP model and use the appropriate tools to be effective in isolating and resolving issues with successful communication on an TCP/IP network. For a download of the entire . Some common questions to ask during troubleshooting include the following: What works? What does not work? How are the things that do and do not work related? Have the things that do not work ever worked? If so, what has changed since it last worked? The answers to these questions can indicate where to begin troubleshooting, possibly allowing you to isolate the component, layer, or configuration issue that is causing the problem. Windows Troubleshooting Tools. Windows Server 2. Windows XP provide a full set of configuration, administration, and diagnostic tools and services that can be used to troubleshoot TCP/IP problems, as listed in Table 1. Table 1. 6- 1 Tools and Services for Troubleshooting TCP/IPTool. Description. Arp. Allows viewing and editing of the Address Resolution Protocol (ARP) cache. Hostname. Displays the host name of the computer. Ipconfig. Displays the current TCP/IP configuration for both IPv. IPv. 6. Also used to manage Dynamic Host Configuration Protocol (DHCP)- allocated IPv. DNS client resolver cache, and register DNS names. Nbtstat. Displays Net. BIOS over TCP/IP (Net. BT) configuration and allows management of the Net. BIOS name cache. Netsh. Configuration tool for many network services. For each network service, there is a context containing commands specific for that service. For the netsh interface ip and netsh interface ipv. TCP/IP protocol settings on either the local computer or a remote computer. Netstat. Displays protocol statistics and information on current TCP connections. Nslookup. Performs DNS queries and displays the results. Ping. Sends Internet Control Message Protocol (ICMP) Echo or Internet Control Message Protocol for IPv. ICMPv. 6) Echo Request messages to test reachability. Route. Allows viewing of the IPv. IPv. 6 routing tables and editing of the IPv. Tracert. Sends ICMP Echo or ICMPv. Echo Request messages to trace the network route taken by IPv. IPv. 6 packets to a specific destination. Pathping. Sends ICMP Echo or ICMPv. Echo Request messages to trace the route an IPv. IPv. 6 packet takes to a destination and displays information on packet losses for each router and link in the path. SNMP service. Provides status and statistical information to Simple Network Management System (SNMP) management systems. Event Viewer. Records errors and events. Performance Logs and Alerts. Logs TCP/IP core protocol performance and sends alerts (the SNMP service must be installed). Network Monitor. Captures and displays the contents of TCP/IP packets sent to and from computers running Windows Server 2. Netdiag. Runs a series of diagnostics test on networking components. Netdiag is installed as part of the Windows XP and Windows Server 2. Support Tools in the Support\Tools folder of the Windows XP or Windows Server 2. CD- ROM. Telnet. Tests TCP connection establishment between two nodes. Ttcp. Listens for and sends TCP segment data or UDP messages between two nodes. Ttcp. exe is provided with Windows XP Service Pack 2 in the Valueadd\Msft\Net\Tools folder of the Windows XP Service Pack 2 CD- ROM. Troubleshooting IPv. The following sections describe the tools and techniques used to identify a problem at successive layers of the TCP/IP protocol stack that is using an IPv. Internet layer. Depending on the type of problem, you might do one of the following: Start at the bottom of the stack and move up. I have a windows 2003 server setup as an open VPN server and I can connect to it no problem. I cannot however ping the server's ip address e.g. 10.8.0.1 or. WinFS (short for Windows Future Storage) was the code name for a canceled data storage and management system project based on relational databases, developed by. Will it get internet access or the user will not be allowed internet. Windows 2000 and Windows XP: Using a Linux L2TP/IPsec VPN server with Windows 2000/XP: Windows Vista: Using a Linux L2TP/IPsec VPN server with Windows Vista. Start at the top of the stack and move down. The following sections are organized from the top of the stack and describe how to: Verify IPv. Verify DNS name resolution for IPv. Verify Net. BIOS name resolution. Verify IPv. 4- based TCP sessions. Although not specified in the following sections, you can also use Network Monitor to capture IPv. IPv. 4- based TCP/IP communications. Network Monitor is provided with Microsoft Systems Management Server and as an optional network component with Windows Server 2. However, to correctly interpret the display of IPv. Network Monitor, you must have an advanced knowledge of the protocols included in each packet. Verifying IPv. 4 Connectivity. You can use the following tasks to troubleshoot problems with IPv. Error messages for Windows XP Pro. Code: Error Message: 0: The operation completed successfully. 1: Incorrect function. Today, we want to share with you another big thing that you will first see in the developer channel for Opera for computers. We are the first major browser maker to. Solution #1: Add a prefix policy to prefer IPv4 addresses over IPv6. Prefix policy table is similar a routing table, it determines which IP addresses are preferred. Repair the connection. Verify configuration. Manage configuration. Verify reachability. View and manage the IPv. Verify router reliability. Repair the Connection. The Network Connection Repair feature can be used to quickly renew IPv. Network Connection Repair performs a series of tasks that attempt to renew the connection as if it were just initialized. To access Network Connection Repair, do the following: Click Start, click Control Panel, and then double- click Network Connections. Right- click the connection that you want to repair, and then click Repair. You can also click Repair on the Support tab for the status of a network connection. The tasks that are performed by Network Connection Repair are the following: Checks whether DHCP is enabled and, if enabled, sends a broadcast DHCPRequest message to refresh the IPv. Flushes the ARP cache. This is equivalent to the arp - d * command. Flushes and reloads the DNS client resolver cache with entries from the Hosts file. This is equivalent to the ipconfig /flushdns command. Re- registers DNS names using DNS dynamic update. This is equivalent to the ipconfig /registerdns command. Flushes and reloads the Net. BIOS name cache with #PRE entries in the Lmhosts file. This is equivalent to the nbtstat - R command. Releases and then re- registers Net. BIOS names with the Windows Internet Name Service (WINS). This is equivalent to the nbtstat - RR command. Verify Configuration. To check the current IPv. The display of the ipconfig /all command includes IPv. DNS settings for all interfaces. The Ipconfig tool only works on the local computer. The display of the netsh interface ip show config command includes DNS and WINS servers per interface. Netsh can also be used to show the configuration of a remote computer by using the –r Remote. Computer. Name command line option. For example, to display the configuration of the remote computer named FILESRV1, use the netsh –r filesrv. Support tab on the Status dialog box on a network connection. To get the status of a network connection, double- click the connection in the Network Connections folder, and then click the Support tab. The Support tab lists the address type (DHCP or manually configured), the IPv. Click Details on the Support tab to display the media access control (MAC) address, DHCP lease information, DNS servers, and WINS servers. Manage Configuration. To make changes to the IPv. Network Connections folder. From the Network Connections folder, you can make changes to the properties of the Internet Protocol (TCP/IP) component for the appropriate network connection. You can use the netsh interface ip set address command to configure the address type (DHCP or manually configured), the IPv. You can use the netsh interface ip set dns command to configure the source of DNS server addresses (DHCP or manually configured), a DNS server address, and DNS registration behavior. You can use the netsh interface ip set wins command to configure the source of WINS server addresses (DHCP or manually configured) and a WINS server address. You can also use the –r Remote. Computer. Name command line option of the Netsh tool to manage the IPv. Ipconfig commands to manage DHCP addresses. You can use the following commands to manage DHCP addresses: ipconfig /releaseipconfig /renewipconfig /showclassidipconfig /setclassid. For more information about using Ipconfig commands to manage DHCP address configurations, see Chapter 6, . To flush the ARP cache, use the arp –d * command. This command also removes static ARP cache entries. Ping the default gateway. Use the Ping tool to ping your default gateway by its IPv. You can obtain the IPv. Pinging the default gateway tests whether you can reach local nodes and whether you can reach the default gateway, which is used to forward IPv. This step might not succeed if the default gateway is filtering all ICMP messages. Ping a remote destination by its IPv. If you are able to ping your default gateway, ping a remote destination by its IPv. This step might not succeed if the destination is filtering all ICMP messages. Filtering of ICMP messages is prevalent on the Internet. Trace the route to the remote destination. If you are unable to ping a remote destination by its IPv. Use the tracert –d IPv. Address command to trace the routing path to the remote destination. The –d command line option prevents the Tracert tool from performing a DNS reverse query on every near- side router interface in the routing path, which speeds up the display of the routing path. This step might not succeed if the intermediate routers or the destination are filtering all ICMP messages. Filtering of ICMP messages is prevalent on the Internet. Check Packet Filtering. The problem with reaching a destination node might be due to the configuration of Internet Protocol security (IPsec) or packet filtering on the source node, intermediate routers, or destination node that is preventing packets from being sent, forwarded, or received. On the source node, check for the following: Active IPsec policies with the IP Security Monitor snap- in. For computers running Windows Server 2. Routing and Remote Access IPv. Routing and Remote Access snap- in. On intermediate IPv. Windows XP, check for the following: Active IPsec policies with the IP Security Monitor snap- in. On intermediate IPv. Windows Server 2. Routing and Remote Access, check for the following: Active IPsec policies with the IP Security Monitor snap- in. Routing and Remote Access IPv. Routing and Remote Access snap- in. Accessing Your Windows Vista Computer with Remote Desktop . If you want to use the Remote Desktop Connection client to access another computer, see the section entitled . I give you step- by- step instructions shortly, but to give you an overview, the requirements are as follows: You must enable Remote Desktop; it's disabled by default. You also have to specify which user account(s) are to be given access. A password has to be set for any user account that you want to use when connecting remotely. You can't use Remote Desktop to connect to an account that has no password. Your host computer must be reachable over the Internet whenever you want to connect to it; this means that it needs an always- on Internet connection. Cable Internet service usually works this way. If you have a DSL connection that requires you to sign on every time you use it, you need to either use a connection- sharing router device and tell it to keep the connection up 2. Windows to keep your connection open. I show you how shortly. Your Internet connection needs a static (fixed) IP address, or you need to use a dynamic DNS service so that your computer's IP address can be determined from afar. With most cable and DSL Internet service, your connection's IP address can change from day to day. You might be able to ask your ISP for a static address for an added monthly fee. If that's not an option, I show you shortly how to install some free add- on software or use a connection- sharing router that supports dynamic DNS (DDNS). Finally, if you use a shared Internet connection, the router or sharing computer has to be set up to forward incoming requests to the computer you want to reach by Remote Desktop. This sounds complex, but it really isn't that bad. Let's go through the process step by step. You can go about this in other ways, of course, but what I give you here is a procedure that's suitable for a home user with Windows Vista Ultimate edition or a small- office user with the Business version. Enabling Remote Desktop Access to Your Computer. To enable Remote Desktop connections to your computer, follow these steps: Click Start, right- click Computer, and select Properties. Under Tasks, click Remote Settings and then confirm the User Account Control prompt. Select Allow Connections from Computers Running Any Version of Remote Desktop. If you want to grant Remote Desktop access to any Limited users, click Select Users, Add, Advanced, Find Now, and then locate the desired name in the Search Results section. Double- click it. To add another name, click Advanced and Find Now again. Click OK to close all the dialog boxes. At this point, you should do two things to be sure that Remote Desktop has been set up correctly: Click Start, Control Panel. Under Security, select Allow a Program Through Windows Firewall and confirm the User Account Control prompt. On the Exceptions tab, find Remote Desktop in the Exceptions list and be sure it's checked. If it isn't, check it. On the General tab, be sure that Block All Incoming Connections is not checked. Use another computer to test Remote Desktop before you get involved in the Internet part. Use the instructions in the second part of the chapter to open the Remote Desktop client on another computer on your network. As the host name, type in the name of the computer you just set up. Make sure that you can connect over your own local network before proceeding. If you just want to use Remote Desktop within your home or office network, you're finished and can skip ahead to the part of the chapter titled . If the power goes out at your home or office and your computer doesn't start itself up again automatically, you won't be able to connect. Your computer must start up automatically. To set this up on a desktop computer, you need to get to the BIOS setup screen. You can get there when you first power up the computer, or by restarting Windows and waiting for the screen to go black. Be prepared to press the BIOS Setup hot key. The screen tells you what key to press; it's usually the Del or F2 key. When you've gotten to the BIOS setup screen, look for the Power Management settings. Find an entry titled AC Power Recovery, or something similar. Change the setting so that your computer turns itself on when the AC power comes on. On some computers, there is also an option that turns on the computer only if it was on when the power failed. That works, too. Then save the BIOS settings and restart Windows. Besides a 2. 4x. 7 computer, you need a 2. Internet connection. If you have cable Internet service or a type of DSL service that does not require you to enter a username or password, you have an always- on Internet connection already and can skip ahead to the next section. For DSL service that requires sign- on, you need some means of automatically reestablishing the connection whenever your computer starts up or the connection goes down. Microsoft's built- in Broadband connection sign- on software does not provide a reliable way by itself to keep the Internet connection permanently open. You can work around this in three ways: You can see if your DSL provider can upgrade your service to provide a static IP address and always- on service. This might be inexpensive enough to make it worthwhile. You can use a hardware connection- sharing router. The router connects to your DSL modem and your computer(s) to the router. The router makes the DSL connection for you, and you can configure it to keep it going all the time. If you don't have a router already, it's a worthwhile investment to buy one. They cost between $0 (after rebate, when there's a sale) and $7. Chapter 2. 2, . Be sure to enable the router's . Otherwise, the connection might be allowed to close when there is no activity from inside your LAN, and you might not be able to connect later. If you use the Broadband connection feature built into Windows Vista, you can add a third- party program to force Windows to keep the connection open all the time. Although I personally prefer the first two options, the Dyn. DNS Updater program that I discuss later can do this for you, so you can forgo the router if you want to. Next, you must make sure you can locate your computer from out on the Internet. Static IP Address or Dynamic DNSAll Internet connections are established on the basis of a number called an IP address, which is to your Internet connection as your telephone number is to your phone. Your IP address uniquely identifies your computer among all the millions of connected computers worldwide. If you use a shared connection, all your network's computers share one public IP address, much as the phone extensions in an office share one outside telephone number. The question is, when you're somewhere else, how do you find your computer's IP address so that Remote Desktop can establish a connection to it? If you have purchased a static IP address from your ISP, the answer is, they'll tell you. It has four sets of numbers separated by periods and looks something like this: 6. This will always be your computer's number. You can simply type this in when using the Remote Desktop client to connect to your computer. However, static addresses are relatively hard to get and usually carry a monthly surcharge; in some cases, ISPs simply cannot or will not provide them. So although this is worth looking into, it might not be an option. Thus, your computer's IP address can change at any time, and you won't necessarily know what it is when you want to connect from somewhere else. The solution to this problem is to use a free dynamic domain name service (DDNS). It has two parts: First, on a DDNS provider's website, you register a host name, a name of your own choice, attached to one of several domain names that the provider makes available. For example, you might register the host name mycomputer in the domain homedns. Second, you set up dynamic DNS client software that periodically contacts the DDNS provider and informs it of your current IP address. Some Internet connection- sharing routers have a DDNS client built in, or you can download and install a software version on your computer. When this is all set up, you can use the name (mycomputer. Internet. To set up dynamic DNS service at dyndns. View www. dyndns. Internet Explorer. Click Create Account. Select a username and password, and enter these along with your email address in the registration form. Be sure to note the username and password. Read and acknowledge the terms of service, check I Will Create Only One Free Account, and click Create Account. Leave the other information as is and click Add Host. If someone else has claimed the name you chose, change the name or domain and try again until you succeed. Be sure to write down the host name and domain name that you eventually select. Now your DDNS service is set up. Next, you need to set up the DNS client, so that changes to your IP address are sent to dyndns. If you are using an Internet connection- sharing router that supports DDNS, use your router's setup screens to enable DDNS using your dyndns. Your router's setup screen will likely differ from this, but it will generally look something like the one in Figure 4. Figure 4. 0. 2 Configure your router to update your host name using dynamic DNS. If your router doesn't have a DDNS client built in, or if you are not using a hardware router, you have to install a software DDNS client to do the job. You want one that doesn't require any manual intervention to get started and that always runs even when nobody is logged on. This means that you need one that operates as a Windows service rather than as a regular desktop application. The free Dyn. DNS Updater program available from dyndns. Here's how to set it up. If you use Windows Internet Connection Sharing, perform this procedure on the computer that shares its connection with the Internet, whether or not it's the computer that you're enabling for Remote Desktop access. Otherwise, do this on the computer that you're enabling for Remote Desktop access.
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