General Network Troubleshooting

Transcription

1 Overview Contents This document outlines some basic network troubleshooting techniques that can be used to test network connectivity. They are useful when troubleshooting issues with Crystal Enterprise (CE) because CE uses network communication to function. Because the techniques outlined in this document are independent of any software, they can be used in conjunction with any version of CE. INTRODUCTION... 2 PING...2 Usage of PING... 2 TRACERT...4 Usage of TRACERT... 4 NSLOOKUP...5 NETSTAT...7 Usage of NETSTAT... 7 TELNET...9 Usage of TELNET... 9 CONTACTING CRYSTAL DECISIONS FOR TECHNICAL SUPPORT /23/ :00 AM Copyright 2003 Crystal Decisions, Inc. All Rights Reserved. Page 1

2 Introduction This paper introduces and explains troubleshooting techniques for networks that are independent of software. The reason that these techniques are key is that they allow you to test the connectivity of a system on a network at the Operating System (OS) level rather than through software. This type of troubleshooting eliminates software from the equation, making for a clearer test. The document is designed to follow a logical flow for troubleshooting. The tests PING, TRACERT, and NSLOOKUP are placed in the order that they should be performed. PING PING is used to test network connectivity response between two computers on a network. You can think of a PING command like submarines and naval ships that send a ping sound to determine the distance between objects based on the amount of time it takes to receive a response. PING sends a packet in the form of an Internet Control Message Protocol (ICMP) packet. The most important aspect of PING is the fact that it shows whether there is a response from a target computer. In this way you can determine if network communication is possible between two computers. Usage of PING The following parameters can be used with PING. ping [-t] [-a] [-n count] [-l size] [-f] [-i TTL] [-v TOS] [-r count] [-s count] [[-j host-list] [-k host-list]] [-w timeout] destination-list Definitions of parameters: -t Ping the specified host until stopped. To see statistics and continue - type Control-Break; To stop - type Control-C. -a Resolve addresses to hostnames. -n count Number of echo requests to send. -l size Send buffer size. -f Set Don't Fragment flag in packet. -i TTL Time To Live. -v TOS Type Of Service. -r count Record route for count hops. -s count Timestamp for count hops. -j host-list Loose source route along host-list. -k host-list Strict source route along host-list. -w timeout Timeout in milliseconds to wait for each reply. 9/23/ :00 AM Copyright 2003 Crystal Decisions, Inc. All Rights Reserved. Page 2

3 Examples In the examples below, all bold text represents what is typed in at the command prompt. All italicized text represents what displays in response to what was just typed. All IP addresses and server names are used as examples only. For this test to be successful, use valid IP addresses and server names. This example shows a PING to the IP address in which the target computer responds. H:\>ping Pinging with 32 bytes of data: Reply from : bytes=32 time=31ms TTL=46 Reply from : bytes=32 time=31ms TTL=46 Reply from : bytes=32 time=15ms TTL=46 Reply from : bytes=32 time=31ms TTL=46 Ping statistics for : Packets: Sent = 4, Received = 4, Lost = 0 (0% loss), Approximate round trip times in milli-seconds: Minimum = 15ms, Maximum = 31ms, Average = 27ms You can also use domain names in PING, such as (ping This will resolve the name to its IP address and ping that IP. If the domain or alias does not exist, you may see the following: H:\>ping Unknown host Domains and DNS resolution will be covered later in this document.. Some further information about the above example: Packets: Sent = 4, Received = 4, Lost = 0 (0% loss) Packet loss is the loss of data that was sent during a ping. It is not uncommon to see a 25% loss in the case of only pinging four times. However a 75% loss indicates communication issues that are usually physical on the network such as cabling and switches. NOTE Sometimes a computer is connected but there is 100% packet loss or no response from the host computer. This is due to a firewall configuration that is blocking ICMP packets (PINGs). In this case, you should speak to the network administrator. Minimum = 15ms, Maximum = 31ms, Average = 27ms The average response time in milliseconds (ms) indicates the average length of time it took to receive a response from the host computer. This can help you gauge lags that may exist in communication if you have slow transfer rates. Common replies can take anywhere from 2ms to 150ms. Replies ranging 300ms and over are characteristic of network lags. This example shows a PING to the IP address in which the target computer does not respond. H:\>ping Pinging with 32 bytes of data: 9/23/ :00 AM Copyright 2003 Crystal Decisions, Inc. All Rights Reserved. Page 3

4 Request timed out. Request timed out. Request timed out. Request timed out. Ping statistics for : Packets: Sent = 4, Received = 0, Lost = 4 (100% loss), Approximate round trip times in milli-seconds: Minimum = 0ms, Maximum = 0ms, Average = 0ms If the PING receives no response, you can conclude that the communication issue is not software related but is a network issue. TRACERT TRACERT in Windows (TRACEROUTE in Unix) is short for trace route. This basically is a trace of the route that a communication between two computers takes. TRACERT is used to test a lag in communication or the point of network failure on a network (Intranet or Internet) that is causing poor to no connection between two computers. TRACERT sends pings to each of the computers along a route and responds with that data on each hop. If at one point during the trace all responses stop, it can help identify the source of network connectivity issues and whether they are caused by internal or external network conditions. For example, if an Internet Service Provider s Router is not responding, the network issues are external. Usage of TRACERT H:\>tracert Usage: tracert [-d] [-h maximum_hops] [-j host-list] [-w timeout] target_name Options: -d Do not resolve addresses to hostnames. -h maximum_hops Maximum number of hops to search for target. -j host-list Loose source route along host-list. -w timeout Wait timeout milliseconds for each reply. Example: In the examples below, all bold text represents what is typed in at the command prompt. All italicized text represents what displays in response to what was just typed. NOTE An asterisk (*) indicates that there was no response for that PING. It is not uncommon to see one asterisk on a hop. H:\>tracert Tracing route to over a maximum of 30 hops 1 <10 ms <10 ms <10 ms <10 ms <10 ms <10 ms internal.server.com [ ] 3 <10 ms 16 ms <10 ms /23/ :00 AM Copyright 2003 Crystal Decisions, Inc. All Rights Reserved. Page 4

5 4 <10 ms <10 ms <10 ms ms <10 ms <10 ms internal2.server.com [ ] 6 <10 ms 16 ms <10 ms internal3.server.com [ ] 7 <10 ms <10 ms <10 ms <10 ms <10 ms 16 ms <10 ms <10 ms <10 ms ge4-1.wanb-vancbc.ip.grouptelecom.net ] 10 <10 ms 15 ms <10 ms ge3-0.peera-sttlwa.ip.grouptelecom.net [ ] ms <10 ms 16 ms bpr2-so seattleswitchdesign.cw.net [ ] 12 <10 ms 15 ms 16 ms acr2-so seattle.cw.net [ ] ms 15 ms 32 ms dcr1-loopback.santaclara.cw.net [ ] ms 31 ms 16 ms bhr1-pos-0-0.santaclarasc5.cw.net [ ] ms 32 ms 31 ms csr21-ve243.santaclarasc4.cw.net [ ] ms 31 ms 31 ms google-exodus.exodus.net [ ] ms * 15 ms ms 15 ms 32 ms Trace complete. Note that the trace goes through each component on the network until it reaches its destination. Three PING response times are given for each hop on the route that are show in milliseconds. NSLOOKUP NSLOOKUP stands for Name Server Look Up. Domain Name Servers (DNS) are the servers on an Intranet or on the Internet that handle converting names such as or into a corresponding IP address such as NSLOOKUP is a way to log on to a DNS server and see what its response is for a particular domain, alias, or IP (reverse look-ups) NSLOOKUP can be used when a computer can ping an IP address but not the alias of that IP address. You can use NSLOOKUP to verify that the computer s DNS server can resolve the alias of the IP address. NOTE Another way to see what DNS servers a machine is using: Microsoft Windows NT, 2000, or XP: Start > Run > cmd > IPCONFIG /ALL Microsoft Windows 95, 98, and ME: Start > Run > winipcfg > OK Click More Info on the resulting window. Unix: Ifconfig Examples: The following example shows a standard search on the alias on the default DNS server that is used by the computer running NSLOOKUP. 9/23/ :00 AM Copyright 2003 Crystal Decisions, Inc. All Rights Reserved. Page 5

6 In the examples below, some of the server names and IP addresses have been changed to invalid placeholders. This is for example purposes only. Your server names and IP addresses will appear when you use NSLOOKUP. In the examples below, all bold text represents what is typed in at the command prompt. All italicized text represents what displays in response to what was just typed. H:\>nslookup Default Server: someserver.somedomain.com Address: > Server: someserver.somedomain.com Address: Non-authoritative answer: Name: Address: Aliases: To see all of the associated records for the domain google.ca, change the q of NSLOOKUP: H:\>nslookup Default Server: someserver.somedomain.com Address: > set q=any > google.ca Server: someserver.somedomain.com Address: Non-authoritative answer: google.ca internet address = google.ca internet address = google.ca internet address = google.ca nameserver = ns1.google.com google.ca nameserver = ns2.google.com google.ca nameserver = ns3.google.com google.ca nameserver = ns4.google.com google.ca primary name server = ns1.google.com responsible mail addr = dns-admin.google.com serial = refresh = (6 hours) retry = 3600 (1 hour) expire = (12 days 33 mins 20 secs) default TTL = (1 day) google.ca MX preference = 10, mail exchanger = smtp1.google.com google.ca MX preference = 20, mail exchanger = smtp2.google.com google.ca MX preference = 30, mail exchanger = smtp3.google.com ns1.google.com internet address = ns2.google.com internet address = ns3.google.com internet address = /23/ :00 AM Copyright 2003 Crystal Decisions, Inc. All Rights Reserved. Page 6

7 ns4.google.com internet address = > This returns the entire zone file for the domain google.ca. This is important to be able to see the DNS servers that the domain is hosted on, the MX or mail record that the domain uses and the preference in which these MX records are set. If you want to run a query on the alias where it is hosted, change the server in NSLOOKUP. An example of this is shown below: H:\>nslookup Default Server: someserver.somedomain.com Address: > server ns1.google.com Default Server: ns1.google.com Address: > Server: ns1.google.com Address: Name: Address: Aliases: > NSLOOKUP can be a very powerful tool if you are connected to another computer by its Fully Qualified Domain Name (FQDN) or an alias such as server.domain.com. NSLOOKUP can tell you what DNS servers the host computer is using and what those DNS servers are resolving a name to. If the IP that the DNS server returns is not correct, it may explain connection issues. NETSTAT NETSTAT shows network status by supplying the contents of various network related data structure in various formats. It displays protocol statistics and current TCP/IP network connections. The format depends on which parameters are used. Usage of NETSTAT The following section outlines how TRACERT can be used with various parameters to display protocol statistics and current TCP/IP network connections. NETSTAT [-a] [-e] [-n] [-s] [-p proto] [-r] [interval] -a Displays all connections and listening ports. -e Displays Ethernet statistics. This may be combined with the -s option. -n Displays addresses and port numbers in numerical form. -p proto Shows connections for the protocol specified by proto; proto may be TCP or UDP. If used with the -s option to display per-protocol statistics, proto may be TCP, UDP, or IP. 9/23/ :00 AM Copyright 2003 Crystal Decisions, Inc. All Rights Reserved. Page 7

8 -r Displays the routing table. -s Displays per-protocol statistics. By default, statistics are shown for TCP, UDP and IP; the -p option may be used to specify a subset of the default. interval Redisplays selected statistics, pausing interval seconds between each display. Press CTRL+C to stop redisplaying statistics. If omitted, netstat will print the current configuration information once. Example: The following example shows all established connections with IPs and ports in which they are connected In the examples below, the IP addresses have been changed to invalid placeholders. This is for example purposes only. Your IP addresses will appear when you use NETSTAT. In the example below, all bold text represents what is typed in at the command prompt. All italicized text represents what displays in response to what was just typed. H:\>netstat -n Active Connections TIP: Try netstat an for a very detailed view of connections and open ports Proto Local Address Foreign Address State TCP CLOSE_WAIT TCP CLOSE_WAIT TCP CLOSE_WAIT TCP ESTABLISHED 9/23/ :00 AM Copyright 2003 Crystal Decisions, Inc. All Rights Reserved. Page 8

9 TELNET TELNET can be used to test connectivity for different services that run on open ports. TELNET is used to connect to a computer on a port and test the connectivity of a service running on that computer. It is most commonly used to test Post Office Protocol (POP), SMTP, and Web Servers. Usage of TELNET H:\>telnet /? telnet [host [port]] host port specifies the hostname or IP address of the remote computer to connect to. Specifies the port number or service name. Basic Commands This section outlines basic commands when using TELNET. In the examples below, all bold text represents what is typed in at the command prompt. All italicized text represents what displays in response to what was just typed. All IP addresses and server names are used as examples only. For this test to be successful, use valid IP addresses and server names. If you type: H:\>telnet You will see: Microsoft (R) Windows 2000 (TM) Version 5.00 (Build 2195) Welcome to Microsoft Telnet Client Telnet Client Build Escape Character is 'CTRL+]' Microsoft Telnet> For a list of commands available in TELNET, type? : Microsoft Telnet>? Commands may be abbreviated. Supported commands are: close display open quit close current connection display operating parameters connect to a site exit telnet 9/23/ :00 AM Copyright 2003 Crystal Decisions, Inc. All Rights Reserved. Page 9

10 set set options (type 'set?' for a list) status print status information unset unset options (type 'unset?' for a list)?/help print help information Microsoft Telnet> To troubleshoot services, set LOCAL_ECHO so that you can see what you are typing when connected: Microsoft Telnet> set LOCAL_ECHO POP POP is an Internet protocol used when accessing your . POP uses the port 110 To test a computer running a POP server you must connect to the name or IP of the computer that has the POP service and specify port 110 as the port to connect to. For example: Microsoft Telnet> open VANEXCH You should see something similar to this (screen will vary depending on the type of POP server running): +OK Microsoft Exchange POP3 server version ready This means you have a successful connection to the service. This verifies that the service is up and running. To log in type the following: (replace <username> with your username): user <username> If it is a valid user name, you should see the following: +OK Then type the following: (replace <password> with your password): pass <password> If it is a valid password for the user name, you should see: +OK This would show that you are able to log into the mail server with a valid account. To see the mail in that account: LIST 9/23/ :00 AM Copyright 2003 Crystal Decisions, Inc. All Rights Reserved. Page 10

11 This is a list of mail messages with an index on the left and the message size To read a message type the following(replace <index> with the indexed you wish to read): RETR <index> The message should then display with its full message headers and body. If all of these tests are successful, you know that the POP service on the machine is functioning properly. If they are not all successful, you know that SMTP SMTP stands for Sending Mail Transfer Protocol and is used to send and receive from server to server. SMTP uses port 25. To test an SMTP service on a computer through TELNET, type the following replacing yourmailserver.com with the actual name of your mail server: Microsoft Telnet> open yourmailserver.com 25 The following are directions to send mail through TELNET to test the SMTP service. Lines in bold are what is typed. Replace example the addresses with valid addresses: Connected to yourmailserver.com. Escape character is '^]'. 220 mx.yourmailserver.com ESMTP Sendmail /8.12.9; Thu, 12 Jun :06: helo frommail.com 250 main.signalq.com Hello [ ], pleased to meet you mail from: butter22333@frommail.com butter22333@frommail.com... Sender ok rcpt to: webmaster@yourmailserver.com webmaster@yourmailserver.com... Recipient ok data 354 Enter mail, end with "." on a line by itself Subject: test message this is a test h5ch6gvi Message accepted for delivery 9/23/ :00 AM Copyright 2003 Crystal Decisions, Inc. All Rights Reserved. Page 11

12 NOTE Notice how the domain of helo frommail.com and the domain of match. This is due to relaying permissions that are set on the mail server. Usually an administrator only allows valid users from valid domains that the SMTP server is sending mail for. Web Servers Web servers commonly run on port 80. To test a web server, telnet to port 80 by typing the following: Microsoft Telnet> open 80 Now if you type any character and press Enter you should get a response similar to the one shown below. HTTP/ Bad Request Date: Wed, 10 Jan :24:37 GMT Server: NCSA/1.5 Content-type: text/html <HEAD><TITLE>400 Bad Request < /TITLE> < /HEAD> <BODY><H1>400 Bad Request < /H1> Your client sent a query that this server could not understand.<p> Reason: Invalid or unsupported method.<p> < /BODY> If you receive this response, the web server is running. Contacting Crystal Decisions for Technical Support We recommend that you refer to the product documentation and that you visit our Technical Support web site for more resources. Self-serve Support: Support: Telephone Support: 9/23/ :00 AM Copyright 2003 Crystal Decisions, Inc. All Rights Reserved. Page 12