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  1. #1
    3 Star Lounger Backspacer's Avatar
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    Diagnosing slow LAN

    It appears that there is something wrong with the LAN in our store. I'm not totally sure of this, but I need to figure it out. I had a different thread going about doing a drive mirror to a directory on a different system. The source system has 1Gb Ethernet and a 7200 RPM drive. The destination system has a 100Mb Ethernet adapter and I think a 5400 RPM drive. The guess for imaging the drive was 2 hours. Actual time was 18 hours. There have been a lot of other indications that the LAN has been either slow or has a lot of delays.

    I will be in the store on Tuesday and Wednesday and I plan to go through all of the cabling and make sure it's in good order. And I will inventory the specified speeds of every device. I'll check for blinking red lights, etc.

    I do not have a network sniffer nor the budget to buy one.

    I will use tracert from and to the various systems to try and see if I can deduce a problem location or area.

    If these do not produce results, I am wondering if anyone can offer a strategy using free or inexpensive software to help nail this down? Is there something out there that shows indications of line condition?

    What would really be cool would be a program that would reside on each of my systems, talk to each other, and build a map of the LAN showing every bit of detail possible to know. I would gladly pay for this just to leave it in place for ongoing maintenance.

    Thanks.

  2. #2
    Super Moderator RetiredGeek's Avatar
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    Backspacer,

    More Info Please.
    1. Make & Model of Router(s)
    2. Total number of devices on the Router.
    3. Any Hubs in the network (Powered or UnPowered)
    4. Total length of cabling (shielded/unshielded)
    5. Any devices generating powerful electro/magnetic emissions (large motors, ham radio/CB radio, etc.)

    May the Forces of good computing be with you!

    RG

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  3. #3
    3 Star Lounger Backspacer's Avatar
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    Here's what I can answer before being there on Tuesday.
    The Internet connection is ADLS, so there is a DSL router, make and model unknown. This router is used solely as a modem and is not connected to the LAN.
    The main gateway router is a ZyXel Zywall USG-20w. It has a built in Gigabit Ethernet four port switch on the LAN side. That router is the DHCP server for the LAN, though the computers and printer have fixed IP addresses.
    There is a rack (not a 19" rack, a 24" square by 6' tall Metro cart which is much more versatile) in the back room with those two routers on it as well as a networked printer and two computers. There is a switch on that rack which is connects those devices to a LAN port on the router.
    The store is wired for Ethernet. I think it was wired with Cat 6, though it could be Cat 5e which would probably slow me down somewhat. There are numerous other devices "out there" in the store: credit card terminals and two more computers. All of that goes to a patch panel high on the wall in a back room. There is a switch there and one cable that leads to another LAN port on the router.
    There are no hubs.
    No way to know the total length of cabling as much of it is buried in the walls. I doubt that any one cable is more than about 30 feet long. The whole store is wired, but our equipment is all situated close to the back room. (It's right behind the main counters.)
    No powerful electro/magnetic emissions. We're just a small gift store in a tiny tourist town way out in the boonies. :-)
    Last edited by Backspacer; 2013-09-01 at 15:29.

  4. #4
    Super Moderator RetiredGeek's Avatar
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    BackSpacer,

    What speed are the switches? If they are only 10/100 that's a big bottleneck. Even if they are GB switches if only one of them is connected to the router you've just limited the max for all units combined to 1Gb when ever they go through the router. A graphic of the wiring setup would be most helpful (to both those trying to supply answers and to you for documentation and diagnosis of problems).

    Unless I miss my guess or don't understand your setup the switch should not be connected to the LAN port on the router that if for the external (internet) connection. I'm guessing here as my experience is limited to very small business/home lans. HTH
    May the Forces of good computing be with you!

    RG

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  6. #5
    3 Star Lounger Backspacer's Avatar
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    I think the two switches are both Gigabit, but I won't know for sure until I am in the store on Tuesday evening and can confirm it. Two heavily used systems are together on one switch along with the credit card terminals and none of them exhibit any slowness at all, much less any that could be attributed to the network. One heavily used and one lightly used system are on the other switch with the networked printer which is rarely used. It is between those two systems where I experienced the very slow backup. But that heavily used system is also slow when using RDP. I'm not at all sure it is the network. It's just something that I need to take a look at.

    Both of those switches are connected to the LAN ports on the ZyXel gateway router. It is our main router. The Internet port on that ZyXel router is connected to a DSL router which is really just setup to work as a DSL modem. My point in telling you that at all was just to get anything Internet out of the picture.

  7. #6
    3 Star Lounger Backspacer's Avatar
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    Let me ask for a clarification: if you have a four port Gigabit switch that doesn't mean that you can do Gigabit switching on all ports simultaneously? If the total throughput is only 1Gb, then no port can ever really operate at 1Gb because it takes two ports to make a transmission. So why have 1Gb Ethernet adapters on our computers? Am I missing something or are we all just being duped (again!) by marketing hacks?

  8. #7
    Super Moderator RetiredGeek's Avatar
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    BackSpacer,

    On a full duplex Gigabit Router each port should work at 1Gb. However, If you have a switch plugged into one of those ports all the devices on that switch share its 1Gb when they communicate with the router. I hope that's a bit clearer.
    May the Forces of good computing be with you!

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  9. #8
    3 Star Lounger Backspacer's Avatar
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    Yes, now I understand what you were saying and it makes perfect sense. So let me clarify some things.

    • Computers A and B are each connected to Switch X.
    • Switch X is connected to LAN (switch Z) port 1 on gateway router.
    • Computers C and D are each connected to Switch Y.
    • Switch Y is connected to LAN (switch Z) port 2 on gateway router.


    Computer A communicates with Computer B. The packets go through Switch X at potentially 1Gb.
    Computer C communicates with Computer D. Those packets go through Switch Y at potentially 1Gb.
    Computer A communicates with Computer C. The packets go through all three switches, but still all at potentially 1Gb?
    Computer A communicates with both Computer B and computer C. Switch X would limit each computer to 500Mb, but it doesn't matter because each computer will only get 500Mb from the port on Computer A, anyway.
    Computer A communicates with Computer C and at the same time Computer B communicates with Computer D. The packets from both comms are going through all three switches at the same time and so communication only gets 500Mb of bandwidth.

    Have I got that right? If so, then my backup shouldn't be slowed by the network because C and D are on the same switch and I did it at night when the other systems were idle. Some extraneous communication would have been going around amongst those computers, but very little.

    Computer C is having lots of slowing problems. It is most noticeable in communications with Computer A where two databases are located, not just with the backup that prompted this thread. I'm starting to wonder if Switch Y really is 1Gb.

    I will be in the store on Tuesday and will double check on the speed of the switches.

  10. #9
    Super Moderator RetiredGeek's Avatar
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    Backspacer,

    Another thing you might want to check on is the health of the destination HD. If this disk is highly fragmented and/or is developing bad sectors this could have a severe impact on the performance of the backup.
    May the Forces of good computing be with you!

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  11. #10
    3 Star Lounger Backspacer's Avatar
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    Ooooh, good idea! I can check that right now. It is a little used, old computer that was relegated to be my remote system rather than toss it in the trash, so who knows what state the drive is in.

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    3 Star Lounger Backspacer's Avatar
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    Well, I see that the drive gets defragged on schedule, the last date being 8/28.
    I'm running chkdsk now ...
    OK, the bad news: I started chkdsk which had to run after a restart. I restarted the system. It is a remote system. After over an hour it is still not accessible from Remote Desktop. The good news: there is someone in the store who can hard restart the system. There is no local monitor so unless there is a useful log entry I guess I'll never know how it went. Ah well.

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    Computers A and B are each connected to Switch X.
    Switch X is connected to LAN (switch Z) port 1 on gateway router.
    Computers C and D are each connected to Switch Y.
    Switch Y is connected to LAN (switch Z) port 2 on gateway router.

    I am not a network expert and I am using the terms switch and router interchangeably. Why do you need switch x and switch Y? Just connect everything to switch Z. If not enough ports, replace switch Z with one with more ports.

    So DSL comes into modem, which passes to a big switch 8, 16, 24, 48 ports. (sounds like 8 or 16 would meet your needs). Everything plugs into one switch/router. We use unmanaged switches, so we cannot get change anything (or goof anything up). Lan problems are almost always a configuration issue ,rarely a cabling issue.

    Finally, check out spiceworks for local/remote monitoring of networks and connection to IT pros. http://www.spiceworks.com/

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    3 Star Lounger Backspacer's Avatar
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    Thank you for that link. I will check out spiceworks.

    A router and a switch are not interchangeable. A router receives a packet and then decides where to send it. A switch receives a packet and broadcasts it back out to all of its ports. Our gateway router does have a switch built into it which is why it is able to have four LAN ports on the back.
    There are two reasons to have a switch. One is to connect multiple devices to a single cable. That's kind of like a hub except for reason number two: a switch prevents collisions which can greatly reduce the overall efficiency of the network. For that reason I make sure that each device on my network goes through a switch.

    The reason I have two external switches is that my network is spread out and this is what works with the cabling that is in the walls. Some of the devices are connected to RJ-45 ports nearby and those cables lead to a patch panel. There is a switch at that patch panel. Another cable on that patch panel leads to the router location. Two registers are located together and feed into another switch which is connected to another port on the gateway router. And there is a network printer plugged in, uh, somewhere!

  15. #14
    3 Star Lounger Backspacer's Avatar
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    Well I found the problem with my LAN. I'm embarrassed to say that one of my switches was just a 10/100 switch. I was sure I had replaced that, but I guess not. I know I bought one, but now I can't find it, so I ordered a new one. In the meantime I have rejiggered the wiring so the least important devices are going through that slow switch and the important register is wired directly into one of the router's LAN ports. I'll probably be back over there next week to install the new switch and everything will be fine again.

    Thank you, RetiredGeek, for drawing my attention to those switches!

  16. #15
    Super Moderator RetiredGeek's Avatar
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    Backspacer,

    Glad you got it sorted!
    May the Forces of good computing be with you!

    RG

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