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Comcast Modem, Router problem

By macojoe ยท 4 replies
Oct 28, 2005
  1. I have a Motorola Modem (SB5120) from Comcast, I have connected to a Belkin router (F5D5230-4)

    The Problem I am having is that when I hook the Modem alone I have super speed downloads and I stay connected all the time.

    When I am hooked to the modem and then to the router, my speed is cut almost in half and on some sites I get disconnected??

    One site told me to ck my TCP config to see if I can increase my TCP connections.
    It was set at auto sense, I called Belkin and they said that I should change the setting to 10baseT, and to download the new Firmware from there site.

    I did all of the above, still slow, but a bit faster. Still get disconnected but it finds it self and reconnects most of the time?

    What I would like to do is connect the main computer direct to the modem and then the other 2 computers thur the router.
    But I am not sure if I can, or not and how??

    The Modem has a USB port or a Wier connector, but you can only use one??
    Is there a splitter of some kind that I can get??

    Sorry for such a long first post!! But i am trying to give you all the info I can.

    O yea I run a Dell 4400 Pentium 4, 1.6 MHz, 512 ram, 165 gig HD, CDrom, CD burner and Floppy

  2. Samstoned

    Samstoned TechSpot Paladin Posts: 1,018

    I am running on comcast with motorola modem through linksys router speeds are a little slower than a direct connection I have tried to fix ,still working on it
    my speeds have increased to toast.net average 3mb's
    dslreports 2.5mb/s
    sometimes as high as 5.5mb/s
    my router is set as a gateway dynamic wan ip addressing
    router itself static lan ip of
    the nic's are all set to static with a full duplex 100 on 2 and full duplex 1000 on 2
    when I set my mtu to 1500 seems to slow me down
    my friend is on comcast with a diff modem and a linksys voip router(mines vpn)he is gettin a steady 5mb/s dwnld
    his setting are dhcp inabled dynamic lan ip and wan
    his dynamic lan is
    this are not real time dwnlds of course ,just speed tests
    I have had my dwnlds real tested with 100mb files
    fastest was 1.8mb/s average
  3. jobeard

    jobeard TS Ambassador Posts: 10,845   +897

    MTU sizes and packet fragmentation

    There's a good write up on MTU size and the effect of sending a packet that's too large.
    The article specifically addresses PPPoE, but the explanation of packet fragmentation is still applicable.
    Conclusion: MTU 1492 is a much better default.
  4. macojoe

    macojoe TS Rookie Topic Starter

    I think I am more confused then ever now!! LOL

    So I guess what I would like to know right now, is there away to split the line coming out of the Cable Moden so I can go derict to my computer and another wire to the router for the other computers??
  5. jobeard

    jobeard TS Ambassador Posts: 10,845   +897

    NO. The connection from the modem is Either/OR but not both.

    try this test:
    ping -f -l [packet] [gateway]

    "Packet" is the size you want to determine and "gateway" is your isp's gateway ip address. So, if you wanted to test packet size, you'd type the following:

    ping -f -l 1492 $gateway

    If your return comes back saying "packet must be defragmented" or something to that effect, then your packet size is still too large. you decrease until it starts reporting timings ​
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