QUESTIONS REGARDING KEEPALIVE.

ITEM: RTA000040684



QUESTION:                                                                       
My customer is trying to use a PC running Sun's PC-NFS as a                     
workstation to his RS/6000s.  He has encountered a problem wherein              
PC-NFS appears to 'time out'.  The specific scenario is as follows:             
Before leaving in the evening, he reboots the PC, and verifies                  
that he can ping the RS/6000s and vice versa.  Some time later,                 
(often the next morning), he finds that he is unable to ping                    
from the PC or vice versa.  The only way to recover is to reboot.               
His PC-NFS configuration is very simple, no nfs files, no                       
access of print services, only tcp/ip connection.                               
                                                                                
Customer has called Sun technical support and they have told him                
that this is because PC-NFS does not support keepalive packets.                 
                                                                                
While I have read a number of items on keepalive, I am not                     
very familiar at this level of tcp/ip.  My questions are:                       
1. Given that the keepalive and keepidle are associated with                    
sockets, does keepalive come into play in the scenario above,                   
where there are no applications (e.g. telnet, ftp, etc)                         
running?                                                                        
2. What do these keepalive packets look like on an iptrace/ipreport?            
                                                                                
Your comments are appreciated.                                                  
                                                                                
---------- ---------- ---------- --------- ---------- ----------                
A: I will address your questions in the order you asked them.                   
                                                                                
1) Correct.  The tcp_keepintvl and tcp_keepidle parameters of the "no"          
   command modify the timing of TCP keep-alive packets.  If there               
   is no TCP connection between the PC and the RISC, then keep-                
   alive packets are not issued by the RISC to the PC.                          
                                                                                
2) TCP keep-alive packets are defined in section 4.2.3.6 of RFC 1122            
   as follows:                                                                  
                                                                                
      "(The) keep-alive mechanism...confirm(s) that an idle                     
       connection is still active...(by) send(ing) a probe segment              
       designed to elicit a response from the peer TCP.  Such a                 
       segment generally contains SEG.SEQ = SND.NXT-1 and may or may            
       not contain one garbage octet of data.  Note that on a quiet             
       connection SND.NXT = RCV.NXT, so that this SEG.SEQ will be               
       outside the window.  Therefore, the probe causes the receiver            
       to return an acknowledgment segment, confirming that the                 
       connection is still live.  If the peer has dropped the                   
       connection due to a network partition or a crash, it will               
       respond with a RST instead of an acknowledgment segment."                
                                                                                
   In other words, in an iptrace/ipreport, the keep-alive packet                
   will contain no data, and it will have the same sequence number              
   as the previous packet on a given TCP connection.                            
                                                                                
   I have appended below a portion of an iptrace I ran which shows              
   several TCP keep-alive packets.  On host "festere", I set the                
   tcp_keepidle to 120 half-seconds (60 seconds).  I then telneted              
   from host "u2e" to "festere".  Because reading an iptrace is                 
   tedious, allow me to describe the trace as though it were a                  
   dialog.  (You may want to print out this item so that you can                
   compare the dialog to the trace more easily.)  I added packet                
   numbers to the trace for easier reference.                                   
                                                                               
(We join our heros soon after a user logged into festere from u2e.)             
                                                                                
u2e: "What is the time, please?" (Request packets not shown.)                   
                                                                                
festere: "Today is Thursday, 24 February 1994, and the time is                  
         16:07:41 CST." (packet 1)                                              
                                                                                
u2e: "Thank you.  My sequence number is th_seq=ef97926a.  I expect              
     your next message to have sequence number th_ack=1737cc59."                
     (packet 2)                                                                 
                                                                                
(One minute later, at 16:08:41...)                                              
                                                                                
festere: "Hello u2e.  My sequence number is th_seq=1737cc58.  Are you           
         still there?" (packet 3)                                              
                                                                                
u2e: "Yes, I am still here (th_seq=ef97926a).  Didn't you already send          
     me a message with sequence number 1737cc58?" (packet 4)                    
                                                                                
(One minute later, at 16:09:41...)                                              
                                                                                
festere: "Hi u2e.  Just wanted to check up on you (th_seq=1737cc58).            
         Please let me know you are OK (th_ack=ef97926a)." (packet 5)           
                                                                                
u2e: "I'm not going anywhere (th_seq=ef97926a) until you send me the            
     right sequence number (th_ack=1737cc59)." (packet 6)                       
                                                                                
(One minute later, at 16:10:41...)                                              
                                                                                
festere: "Yo, u2e (th_seq=1737cc58)¢  Wassup (th_ack=ef97926a)?"               
         (packet 7)                                                             
                                                                                
u2e: "Hey mon (th_seq=ef97926a), I'm like the bunny.  I keep going,             
     and going...unlike you (th_ack=1737cc59)." (packet 8)                      
                                                                                
(Ad infinitum...)                                                               
                                                                                
   Note that if u2e never responded (for example, if I had shut down            
   the Ethernet interface), festere would stop transmitting packets             
   after 8 tries.  Each try would be separated by the value of the              
   tcp_keepintvl parameter.                                                     
                                                                                
*** PACKET 1 ***                                                                
=====( packet transmitted on interface en0 )=====Thu Feb 24 16:07:41 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=72, ip_id=42177, ip_off=0            
        ip_ttl=60, ip_sum=bba6, ip_p = 6 (TCP)                                  
TCP header breakdown:                                                           
                                
        th_seq=1737cc39, th_ack=ef97926a                                        
        th_off=5, flags                                            
        th_win=16060, th_sum=1f47, th_urp=0                                     
00000000     54687520 46656220 32342031 363a3037     |Thu Feb 24 16:07|         
00000010     3a343120 43535420 31393934 0d0a2420     |:41 CST 1994..$ |         
                                                                                
*** PACKET 2 ***                                                                
=====( packet received on interface en0 )=====Thu Feb 24 16:07:41 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=40, ip_id=41001, ip_off=0            
        ip_ttl=60, ip_sum=c05e, ip_p = 6 (TCP)                                  
TCP header breakdown:                                                           
                                
        th_seq=ef97926a, th_ack=1737cc59                                        
        th_off=5, flags                                                  
        th_win=16060, th_sum=e893, th_urp=0                                     
                                                                                
*** PACKET 3 ***                                                                
=====( packet transmitted on interface en0 )=====Thu Feb 24 16:08:41 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=40, ip_id=42278, ip_off=0            
        ip_ttl=60, ip_sum=bb61, ip_p = 6 (TCP)                                  
TCP header breakdown:                                                           
                                
        th_seq=1737cc58, th_ack=ef97926a                                        
        th_off=5, flags                                                  
        th_win=16060, th_sum=e894, th_urp=0                                     
                                                                                
*** PACKET 4 ***                                                                
=====( packet received on interface en0 )=====Thu Feb 24 16:08:41 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=40, ip_id=41058, ip_off=0            
        ip_ttl=60, ip_sum=c025, ip_p = 6 (TCP)                                  
TCP header breakdown:                                                           
                                
        th_seq=ef97926a, th_ack=1737cc59                                        
        th_off=5, flags                                                  
        th_win=16060, th_sum=e893, th_urp=0                                     
                                                                                
*** PACKET 5 ***                                                                
=====( packet transmitted on interface en0 )=====Thu Feb 24 16:09:41 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=40, ip_id=42360, ip_off=0            
        ip_ttl=60, ip_sum=bb0f, ip_p = 6 (TCP)                                  
TCP header breakdown:                                                           
                                
        th_seq=1737cc58, th_ack=ef97926a                                        
        th_off=5, flags                                                  
        th_win=16060, th_sum=e894, th_urp=0                                     
                                                                                
*** PACKET 6 ***                                                                
=====( packet received on interface en0 )=====Thu Feb 24 16:09:41 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=40, ip_id=41106, ip_off=0            
        ip_ttl=60, ip_sum=bff5, ip_p = 6 (TCP)                                  
TCP header breakdown:                                                           
                                
        th_seq=ef97926a, th_ack=1737cc59                                        
        th_off=5, flags                                                  
        th_win=16060, th_sum=e893, th_urp=0                                     
                                                                                
*** PACKET 7 ***                                                                
=====( packet transmitted on interface en0 )=====Thu Feb 24 16:10:41 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=40, ip_id=42379, ip_off=0           
        ip_ttl=60, ip_sum=bafc, ip_p = 6 (TCP)                                  
TCP header breakdown:                                                           
                                
        th_seq=1737cc58, th_ack=ef97926a                                        
        th_off=5, flags                                                  
        th_win=16060, th_sum=e894, th_urp=0                                     
                                                                                
*** PACKET 8 ***                                                                
=====( packet received on interface en0 )=====Thu Feb 24 16:10:41 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=40, ip_id=41148, ip_off=0            
        ip_ttl=60, ip_sum=bfcb, ip_p = 6 (TCP)                                 
TCP header breakdown:                                                           
                                
        th_seq=ef97926a, th_ack=1737cc59                                        
        th_off=5, flags                                                  
        th_win=16060, th_sum=e893, th_urp=0                                     
                                                                                
 ++++++ END OF REPORT ++++++                                                    
                                                                                
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This item was created from library item Q655842      CQKSL                      
                                                                                
Additional search words:                                                        
COMMUNICATIO CQKSL IX KEEPALIVE MAR94 OZNEW QUESTION REGARDING                 
RISCSYSTEM RISCTCP SOFTWARE TCPIP                                               
                                                                                
                                                                                
                                                                                
                                                                                
                                                                                
                                                                                
                                                                                
                                                                                
                                                                                
                                                                                
                                                                                
                                                                                
                                                                                
                                                                               


WWQA: ITEM: RTA000040684 ITEM: RTA000040684
Dated: 04/1996 Category: RISCTCP
This HTML file was generated 99/06/24~12:43:16
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