vb.net 2d barcode free CHapTER 31 Troubleshooting Network Issues in C#

Creator DataMatrix in C# CHapTER 31 Troubleshooting Network Issues

Ping is of limited usefulness today because most new computers drop Ping requests (which use ICMP) . Therefore, you might ping a computer that is connected to the network but not receive any response . Additionally, a computer might respond to Ping requests even if a firewall is dropping all other traffic misleading you into thinking that you had connectivity . However, Ping is still the best tool to easily monitor network connectivity on an ongoing basis . After using PathPing to identify network hosts that respond to ICMP requests, you can use Ping to constantly submit Ping requests and thereby easily determine whether you currently have connectivity to the host . If you are experiencing intermittent connectivity problems, a Ping loop will indicate whether your connection is active at any given time . To start a Ping loop, run the following command .

Replies indicate that the packet was sent successfully, while Request Timed Out messages indicate that the computer did not receive a response from the remote host . The following example indicates how to monitor the connection to a host at the IP address 192 .168 .1 .1 .

ping t 192.168.1.1 Pinging 192.168.1.1 with 32 bytes of data: Reply from 192.168.1.1: bytes=32 time=1ms TTL=64 Reply from 192.168.1.1: bytes=32 time<1ms TTL=64 Reply from 192.168.1.1: bytes=32 time<1ms TTL=64 Reply from 192.168.1.1: bytes=32 time<1ms TTL=64 Request timed out. Request timed out. Request timed out. Request timed out. Request timed out. Reply from 192.168.1.1: bytes=32 time<1ms TTL=64 Request timed out. Request timed out. Reply from 192.168.1.1: bytes=32 time<1ms TTL=64

Note that Ping loops provide only an approximate estimation of connectivity . Ping packets will occasionally be dropped even if connectivity is constant . Additionally, because Ping sends requests sooner if a reply is received than if the reply times out, you cannot use the ratio of replies to time-out errors as a useful indication of network uptime .

ing can be useful in determining whether upstream routers are black hole routers, which drop datagrams larger than a specific size. For more information, see

http://support.microsoft.com/kb/314825.

If you want to use Ping from a Windows PowerShell script, use the Test-Connection cmdlet . The functionality is almost identical to Ping, with the added benefit of being able to specify the Source parameter to initiate the ICMP requests from a remote computer .

Directly query critical services on the remote host to determine whether it is available and accessible . You can use two troubleshooting tools to query services on a remote host: PortQry (Portqry .exe) and Telnet Client . PortQry is more flexible and simpler to use than Telnet Client; however, because it is not included with Windows (but can be downloaded from the Microsoft Web site), it might not be installed on all systems . Use Telnet Client to query remote services only when PortQry is not available . PortQry version 1 .22 is a TCP/IP connectivity testing utility that is included with the Windows Server 2003 Support Tools . For information on how to download these tools, see http://support.microsoft.com/kb/892777 . PortqryV2 .exe is a new version of PortQry that includes all the features and functionality of the earlier version and has new features and functionality . For information concerning PortqryV2 .exe and how to download it, see http://support.microsoft.com/kb/832919 . The following examples can be performed using either version .

command-line port scanner, can be found at http://support.microsoft.com/kb/310099, which includes a link for downloading this tool.

A single computer can host many network services . These services distinguish their traffic from each other by using port numbers . When testing connectivity to an application by using Telnet, you must provide Telnet with the port number that the destination application is using .