INTERMITTENT TELNET SESSIONS

ITEM: RTA000048659



QUESTION:                                                                       
I have a customer with two risc systems that are having telnet sessions         
that time out and connect intermittently.  One machine at 3.2.4 and the         
other at 3.2.5.  Everything worked fine for two weeks.  Also the com-           
munications is token ring.                                                      
                                                                                
---------- ---------- ---------- --------- ---------- ----------                
A: From the text of your question, it is difficult to determine what            
   may be causing the telnet sessions to only connect intermittently.           
   To help assist in matters, I have appended two documents below that          
   I believe may be beneficial to resolving the problem.                        
                                                                                
   The first document is called "Telnet Problem Determination" and the          
   second is "TCP/IP Problem Determination".  I will library this item          
   for future use.                                                             
                                                                                
   If this information fails to resolve the problem, please append with         
   as much specific information as possible to help with the resolution.        
                                                                                
----------------------------------                                              
                                                                                
Telnet Problem Determination                                                    
----------------------------                                                    
                                                                                
1 - Verify the base TCP/IP configuration.  See tcpippd.txt.                     
                                                                                
2 - Verify that the telnet is a subserver of inetd.  Use the                    
    command "inetserv -sIX" or "smit inetdconf"..."List All inetd               
    Subservers".  If telnet is not listed, add it using the                     
    command "smit inetdconf"..."Add an inetd Subserver".                       
                                                                                
3 - Verify that you can telnet to your own IP address.  If you                  
    can't, the base TCP/IP configuration is incorrect.                          
                                                                                
4 - If another host can't telnet into this RISC, run an iptrace                 
    and verify that this RISC is actually receiving the connection              
    request.  Specify the "-p 23" flag when you run the iptrace.                
    The following two packets illustrate what to look for:                      
                                                                                
=====( packet received on interface en0 )=====Mon Mar 14 14:20:28 1994          
ETHERNET packet : . 02:60:8c:2e:bb:11 -> 02:60:8c:2f:31:4e .  type 800          
(IP)                                                                            
IP header breakdown:                                                            
        < SRC =        9.3.6-2.html >  (u2e.austin.ibm.com)                         
        < DST =        9.3.6.35 >  (festere.austin.ibm.com)                    
        ip_v=4, ip_hl=20, ip_tos=0, ip_len=44, ip_id=44727, ip_off=0            
        ip_ttl=60, ip_sum=b1cc, ip_p = 6 (TCP)                                  
TCP header breakdown:                                                           
                                
        th_seq=2a2e3401, th_ack=0                                               
        th_off=6, flags                                                  
        th_win=65535, th_sum=16c3, th_urp=0                                     
00000000     020405b4                                |....            |         
                                                                                
=====( packet transmitted on interface en0 )=====Mon Mar 14 14:20:28 1994       
ETHERNET packet : . 02:60:8c:2f:31:4e -> 02:60:8c:2e:bb:11 .  type 800          
(IP)                                                                            
IP header breakdown:                                                            
        < SRC =        9.3.6.html >  (festere.austin.ibm.com)                     
        < DST =        9.3.6.32 >  (u2e.austin.ibm.com)                        
        ip_v=4, ip_hl=20, ip_tos=0, ip_len=44, ip_id=53448, ip_off=0            
        ip_ttl=60, ip_sum=8fbb, ip_p = 6 (TCP)                                  
TCP header breakdown:                                                           
                                
        th_seq=9b51c201, th_ack=2a2e3402                                        
        th_off=6, flags                                             
        th_win=16060, th_sum=7aa2, th_urp=0                                     
00000000     020405b4                                |....            |         
                                                                                
    Notice the "destination port" and "th_ack" fields in the TCP header         
    breakdown of packet 1.  port=23 indicates that this packet is telnet        
   related.  th_ack=0 indicates this is the first packet in the telnet          
    connection, and so it is the telnet request.  th_ack=2a2e3402 in            
    packet 2 confirms that festere acknowledged u2e's telnet connection         
    request.                                                                   
                                                                                
5 - Obtain a trace of all the data sent on the telnet connection.               
    The trace will be in hexadecimal, and hence very difficult to               
    interpret.  Only use this option when all other avenues of PD               
    fail to identify the problem:                                               
                                                                                
    a) At the shell prompt, enter "telnet -n telnet.out".                       
    b) At the telnet prompt, enter "toggle netdata".                            
    c) At the telnet prompt, enter "open "                  
                                                                                
    Continue with the telnet connection until you have recreated the            
    error.  Then, exit out of telnet.  The file telnet.out will                 
    contain an exhaustive log in hexadecimal of everything sent and             
    received on the telnet connection (i.e. AFTER the TCP connection            
    has been established and the telnet options negotiated).                   
                                                                                
-----------------------                                                         
                                                                                
Contents                                                                        
--------                                                                        
                                                                                
   TCP/IP Problem Determination                                                 
   How to do PD                                                                 
   Common Questions                                                             
   Common Error Messages                                                        
   Other Diagnostic Tools                                                       
                                                                                
TCP/IP Problem Determination                                                    
----------------------------                                                    
                                                                               
TCP/IP problem determination (PD) is the process of finding out as              
quickly as possible why a TCP/IP configuration is not working.  Once            
you know why the configuration is not working, you instantly know               
what you need to do to fix it.                                                  
                                                                                
How to do PD                                                                    
------------                                                                    
                                                                                
Step 1: Draw a picture                                                          
                                                                                
   Effective problem solvers always draw a picture.  Sometimes,                 
   experienced problem solvers do not actually put the picture on paper,        
  but they still draw a picture mentally.  A picture reveals the                
   relationships between objects, and the attributes of those objects.          
                                                                               
   Since you want to do PD as quickly as possible, it is most                   
   efficient to know ahead of time what symbols to use.  In networking,         
   with just six symbols you can draw a wide variety of useful                  
   pictures.  You should know how to draw an Ethernet, a Token Ring,            
   a FDDI ring, dial-up connection, a mainframe channel attachment,             
   and a network station.  Here is how these symbols commonly appear:           
                                                                                
                                             NS (Network Station)               
      Ethernet                             __|__________                        
                                                     |                          
                                                     NS                         
                                              ______                            
      Token Ring                       NS ___|      |___ NS                     
                                             |______|                           
                                                                               
                                             ==========                         
      FDDI Ring                        NS ---||      ||--- NS                   
                                             ==========                         
                                                                                
      Dial up                         NS --------//-------- NS                  
                                                                                
      Mainframe channel attachment    NS ================== NS                  
                                                                                
                                             .-------.                          
      Network Station                  NI ---|       |--- NI (Network           
                                             `-------'        Interface)        
                                                                                
                    Legend of Commonly Used Symbols                             
                                                                                
   The symbols you draw depend on the problem description you                  
   have.  Begin with the symbol for the type of network, and                    
   then add the network stations.  The symbol for the network should            
   have one line attached to it for each network station (e.g. the              
   lines connecting the letters "NS" to the network symbols, as shown in        
  the legend above).  A network station can be a RISC, a mainframe, a           
   router, a PC, etc.                                                           
                                                                                
Step 2: Label the picture                                                       
                                                                                
   From the information given in the problem description, label                 
   all the network stations with the hostname, IP address, and                  
   netmask.  If a network station has multiple interfaces (as shown             
   in the legend above), label each interface completely, including             
   the interface name (e.g. "en0", "tr1", etc.).                                
                                                                               
Step 3: Verify the base configuration.                                          
                                                                                
   All TCP/IP functionality (name resolution, telnet, the r* commands,          
   FTP, NFS, NIS, etc...) relies on correct configuration of the                
   adapter, network interface, and routing table.  An easy way to               
   verify the base configuration is to ping another host (which you             
   know is working correctly) by its IP address.  If the ping succeeds,         
   then you know that the base configuration is correct.                        
                                                                                
   If the ping does not succeed, there are several possible sources             
   of the problem: (1) incorrect software configuration, (2) incorrect          
   adapter configuration or faulty adapter, (3) network problem.                
                                                                                
   First, check the software configuration:                                     
                                                                               
   Q1) Are the IP addresses valid and consistent across all the hosts           
       in the IP subnet?  Use the "ifconfig " command.                     
                                                                                
   Q2) Are the netmasks the same on each host in the IP subnet?  Use            
       the "ifconfig " command.                                            
                                                                                
   Q3) Is the interface up?  Use the command "ifconfig " and               
       look for the flags UP and RUNNING.                                       
                                                                                
   Q4) Is the routing table correct?  Use the the "netstat -rn" command         
       and look for (1) a route to localhost, (2) a route to this host's        
      IP subnet, and (3) a default route out of this host's IP subnet.          
       If the routing table is incorrect, use the "smit route" command          
       to add/remove the appropriate routes.                                    
                                                                               
   Q5) Is inetd running?  Use the "lssrc -s inetd" command.  If not,            
       use the command "startsrc -s inetd" to start it.  Or, use                
       "smit inetd"..."inetd Subsystem".                                        
                                                                                
   Next, check the adapter configuration.  See adapterpd.txt                    
                                                                                
   Finally, check the network itself:                                           
                                                                                
   Q1) Is there are router or gateway between this host and the                 
       remote host?  If so, is it configured correctly?  I.e. can               
       other machines on this physical segment and IP subnet                    
       communicate with the outside world using that router/gateway?            
                                                                                
   Q2) Is there a break in the cabling somewhere?  Is the Ethernet              
       terminated properly?  (This is an area which requires the               
       involvement of a CE or an electrical engineer.  It is beyond             
       the scope of AIX configuration.)                                         
                                                                                
   Once the base configuration is correct, you can proceed with                 
   PD specific to a particular application, such as name service (DNS           
   and NIS), etc.  See: iptrace.txt, nfspd.txt, nispd.txt                       
                                                                                
Common Questions                                                                
----------------                                                                
                                                                                
Q) How can I have two different IP subnets on the same physical Token           
   Ring (or Ethernet) segment?                                                  
                                                                                
A) Install a second network adapter and define an interface for it.             
   Specify the appropriate IP address and netmask.                             
                                                                                
Q) How can I have two adapters (interfaces) on the same IP subnet and           
   the same physical Token Ring (or Ethernet) segment?  Will this               
   improve performance?                                                         
                                                                                
A) This is a violation of TCP/IP architecture.  In other words, it is           
   invalid for a machine to have two IP addresses on the same IP subnet.        
                                                                                
   However, it is possible to configure this, but doing so requires             
   the following kludge: in order to direct traffic over the second             
   adapter, you must specify as many host-specific routes as there              
   are hosts which will use that interface.  Use the command:                   
                                                                                
    route add -host  <2nd_ip_addr> -netmask                  
-interface                                                                     
                                                                                
Q) Can I use en0 and et0 concurrently on the same Ethernet adapter?             
                                                                                
A) Yes.  Each interface should have a unique IP address on different            
   IP subnets.  Also, you may need to explicitly execute the command            
                                                                                
     "route add -net   -netmask  -interface"          
                                                                                
   in order to define a route to the second subnet.                             
                                                                                
Q) I have a RISC acting as a router between two different subnets.  I           
   can ping hosts on both subnets, but hosts on network A cannot ping           
   hosts on network B.  Suggestions?                                            
                                                                                
A) Verify that you have IP forwarding turned on (use the "no -a"               
   command).  If ipforwarding has the value "0" (off), then use the             
   command "no -o ipforwarding=1" to turn IP forwarding on.  By default,        
  IP forwarding is "1", so it may be the case that someone added a              
   command to the end of the /etc/rc.tcpip file to turn IP forwarding           
   off.                                                                         
                                                                                
Q) How can I determine which routes are defined in the ODM and which            
   are defined dynamically?                                                     
                                                                                
A) The OS maintains the kernel routing table in memory.  The route to           
   localhost and the route to the machine's own IP subnet are added             
   to the routing table based on the definition of the network                  
   interface (e.g. tr0, en0).  Static routes are added to the routing           
   table based on route definitions in the ODM.  To see the routes              
   which are stored in the ODM, use the command:                               
                                                                                
      odmget -q "name=inet0 and attribute=route" CuAt                           
                                                                                
Q) How do I determine my machine's hostname?                                    
                                                                                
A) Use the "hostname" command.  SMIT executes this command when you             
   execute "smit hostname" and then select "Show the Hostname".  The            
   hostname command retrieves the hostname from the ODM, which you              
   can do by executing the command:                                             
                                                                                
      odmget -q "name=inet0 and attribute=hostname" CuAt                        
                                                                                
Q: How can I determine that route that a packet takes to a remote               
   host?                                                                        
                                                                               
A: Use the "ping -R " command.                                        
                                                                                
Common Error Messages                                                           
---------------------                                                           
                                                                                
"Error creating listening port"                                                 
                                                                                
This error message could be caused by the following:                            
                                                                                
  a)  System resource controller daemon (srcmstr) in /etc/inittab is            
      not running (use the "ps -ef | grep srcmstr " command to check            
      if the src daemon is running).                                            
                                                                                
      To start the daemon verify that the line:                                 
                                                                               
         srcmstr:2:respawn:/etc/srcmstr    # System Resource Controller         
                                                                                
      in /etc/inittab is uncommented.  If it is not, uncomment it and           
      then issue the "telinit q" command.  Then, verify that the daemon         
      is running with the command "ps -ef | grep srcmstr".                      
                                                                                
  b)  Improperly formatted /etc/services file.  The "white space"               
      separating columns must be tabs, not spaces.  You can determine           
      the type of white space used in the file by issuing the                   
      ":set list" command of vi.  This command reveals hidden                   
      characters in a file.  For example, if you have the line                  
                                                                                
         smtp            25/tcp          mail                                   
                                                                                
      in /etc/services, the ":set list" command will convert it to             
                                                                                
         smtp.I.I25/tcp.I.mail $                                                
                                                                                
      where                                                                     
                                                                                
         .I (carot I) represents the indent character                           
         $ represents the carriage return/line feed characters                  
                                                                                
      If the ":set list" command converts the line to                           
                                                                                
         smtp            25/tcp          mail $                                 
                                                                                
      then you will need to delete the spaces and replace them                  
      with tab (indent) characters.                                             
                                                                               
  c)  The portmap daemon is not running.  Verify that the line                  
                                                                                
         start /usr/etc/portmap "$src_running"                                  
                                                                                
      in /etc/rc.tcpip is uncommented.  If it is not, uncomment it,             
      and then start the daemon with the command "startsrc -s portmap".         
      Verify that the daemon is running with the command                        
      "lssrc -s portmap".  The output should indicate a status of               
      "active".                                                                 
                                                                                
  d)  You may have a faulty adapter or a loose connection at the                
      token ring interface.  Verify that the cable is firmly attached           
      to the adapter.  Also, use the "diag -a" command to check                 
      your adapter.                                                             
                                                                               
Q: When I try to telnet to another RISC, I get the message:                     
                                                                                
     telnet: connect: A remote host refused an attempted connect                
                      operation.                                                
                                                                                
   What's wrong?                                                                
                                                                                
A: Make sure the inetd daemon is running.  Use the command:                     
   "lssrc -s inetd".  If it is not running, start it with the command           
   "startsrc -s inetd", or with "smit inetd"..."inetd Subsystem"..."Start       
   Using the inetd Subsystem".                                                  
                                                                                
Other Diagnostic Tools                                                          
----------------------                                                          
                                                                               
traceroute - comes with NetView/6000, and with 3.2.4 and later.                 
             NOT available via anonymous ftp at Harpo.seas.ucla.edu             
             (129.97.2.211)                                                     
                                                                                
The following three tools reside in the /usr/local/bin directory of u2e.        
They were retrieved via anonymous ftp from burrito.raleigh.ibm.com              
in /pub/lantools as the file trtools_315.tar.Z or trtools_32.tar.Z,             
depending if you have AIX 3.1.5 or AIX 3.2.  Documentation is included.         
                                                                                
trp - token ring ping                                                           
pra - backwards arp (determine IP address from MAC address)                     
mcp - microcode ping (lookup microcode level of remote adapter)                 
                                                                                
-----------------------------------                                             
    END OF DOCUMENTS                                                           
-----------------------------------                                             
                                                                                
---------- ---------- ---------- --------- ---------- ----------                
                                                                                
                                                                                
This item was created from library item Q671544      CVXPL                      
                                                                                
Additional search words:                                                        
COMMUNICATIO CVXPL INTERMITTENT IX OCT94 OZNEW RISCSYSTEM RISCTCP               
SESSION SESSIONS SOFTWARE TCPIP TELNET                                          
                                                                                
                                                                                
                                                                                
                                                                                
                                                                               


WWQA: ITEM: RTA000048659 ITEM: RTA000048659
Dated: 04/1996 Category: RISCTCP
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