network ok???

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Oct 19th, 2007
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Hi,


Appreciate if someone could advise how to show that the network is not the cause of the problem. using ethereal trace, ping, etc? what tests should be taken?


The problem is users experience intermittent slowness in accessing web applications. Navigation from one web link to another takes about 10s.


Thanks!

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JORGE RODRIGUEZ Fri, 10/19/2007 - 04:40
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Hi Christina, we responded to a similar thread a while back , first gather specific information in order to get a baseline to whether is specific to a single weblink destination or weblinks in general so that you can narrow down troubleshooting process..is your problem specific to oubound internet single web link or many links in general or internal web links? from what you are discribing it seems specific internally.. you could use trace, extended pings or monitor physical links utilization or watch whether WAN links are droping packets .., also checking internal DNS issues.


I always say, one uses a packet sniffer as last resource only when you as a network administrator have exausted all angles in the troubleshooting process and have ruled out physical links issues, routing issues, as well as the server administrators have ruled out issues internal to the servers .


check this thread which may help.


http://forum.cisco.com/eforum/servlet/NetProf?page=netprof&forum=Network%20Infrastructure&topic=WAN%2C%20Routing%20and%20Switching&CommCmd=MB%3Fcmd%3Ddisplay_location%26location%3D.1ddfa244/0



HTH

Jorge


rayroyaleverest Fri, 10/19/2007 - 05:16
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On the computer's task manager check the CPU, memory, and page file usage. Also, see if the hard disk is near capacity. A hard disk defragmentation may help. Delete the temporary Internet files.

neo_christina Fri, 10/19/2007 - 06:45
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Hi,


Thanks. System utilization seems fine. Hence, installed monitoring agents on the servers to view its performance.

neo_christina Fri, 10/19/2007 - 06:43
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Hi Jorge,


really appreciate and thanks for your explanation.


1) tried ping from PC to server and the maximum round trip once a while ~700+ms. wonder any baseline on worst data latency acceptance time?


2) neligible outdiscards on the switch port interface connecting to the server.


3) took ethereal trace from PC to server. experience slow/hang for about 9.635539s(logs below)


187 0.319896 PC.windows.ap.com Server.ap.com TCP [TCP Retransmission] [TCP segment of a reassembled PDU]

188 0.656240 PC.windows.ap.com Server.ap.com TCP [TCP Retransmission] [TCP segment of a reassembled PDU]

189 1.203115 PC.windows.ap.com Server.ap.com TCP [TCP Retransmission] [TCP segment of a reassembled PDU]

190 2.406213 PC.windows.ap.com Server.ap.com TCP [TCP Retransmission] [TCP segment of a reassembled PDU]

191 4.812429 PC.windows.ap.com Server.ap.com TCP [TCP Retransmission] [TCP segment of a reassembled PDU]

192 9.635539 PC.windows.ap.com Server.ap.com TCP 3614 > http [SYN] Seq=0 Len=0 MSS=1260


4) a lot of TCP CHECKSUM INCORRECT as shown below.


3399 > http [ACK] Seq=10291 Ack=7285 Win=64804 [TCP CHECKSUM INCORRECT] Len=0

POST /test_weblink/start.swe HTTP/1.1[Unreassembled Packet [incorrect TCP checksum]]


Appreciate if you could share your views. Thanks!

neo_christina Fri, 10/19/2007 - 20:01
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the slowness is intermittent. access is intermittently slow even to only the web server. the rest of the servers depends as they need to receive data from the database.

JORGE RODRIGUEZ Fri, 10/19/2007 - 07:22
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retransmissions requests could be cuased by many factors but usually by somehow packets being drop somewhere along the path either locally to the switchport duplex mismatch where the destination server or servers connect into, check the switch ports on the servers and see if there are CRC, runts, giants etc.


Also do trace route from a source system to dest and observe the ms.


conduct extended ping from source router..

to destination host to see if you get 100% success rate , here is an example

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080093f22.shtml



rayroyaleverest Sat, 10/20/2007 - 11:37
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Sounds like the problem is on the switch port to the web server, or with the web server itself. Try using a different switch port. Also, check the cabling. Check the web server performance parameters.

cntour_2004 Sat, 10/20/2007 - 12:01
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ping your counterpart pc on the same segment. If it's ok then probably you should check your sever side, otherwise use another counterpart to check the link to server to determine whether your PC is all right.

Good luck

neo_christina Sun, 10/21/2007 - 02:29
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hi all,


thanks for your reply. ping from PC to server is ok. however, only when accessing the web page itself. access from one tab to another is intermittently slow. what do you think?



rayroyaleverest Sun, 10/21/2007 - 13:43
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Adding RAM to the server may improve response time. A hard drive defragmentation may help. There may be some inefficiency with the code used to develop the web site. Do the server performance statistics indicate any problems?

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