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Combine two Internet connections

By alanrwood
Oct 16, 2011
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  1. I have two phone lines of which one is used exclusively for ADSL internet access. I am currently reviewing my ISP and phone connection suppliers. It turns out that I can have calls and ADSL on both lines for what I am paying at this moment. I already have 3 routers so what I was wondering is could I tandem two routers, each on different phone lines and with different ISPs in a similar way to what I had some years ago with two ISDN lines to double up on speed and throughput. Is it possible??
  2. jobeard

    jobeard TS Ambassador Posts: 10,309   +788

    NO! here's why.

    Start with the basics of routing. When you get your first ISP connection, two things happen:
    a) you get TCP settings and
    b) a route table is created

    Look at the TCP settings and then the Route table:
    TCP Settings:
    Ethernet adapter Local Area Connection:
            Connection-specific DNS Suffix  . : rr.com
            Description . . . . . . . . . . . : Realtek RTL8139/810x Family Fast Ethernet NIC
            Physical Address. . . . . . . . . : 00-aa-bb-cc-dd-ee
            Dhcp Enabled. . . . . . . . . . . : Yes
            Autoconfiguration Enabled . . . . : Yes
            IP Address. . . . . . . . . . . . :
            Subnet Mask . . . . . . . . . . . :
    [b]        Default Gateway . . . . . . . . . :       << DEFAULT[/b]
            DHCP Server . . . . . . . . . . . :
            DNS Servers . . . . . . . . . . . :
            Lease Obtained. . . . . . . . . . : Friday, September 30, 2011 8:03:27 PM
            Lease Expires . . . . . . . . . . : Monday, January 18, 2038 8:14:07 PM
    Route Table:
    C:\Documents and Settings\Jeff>[b]route print[/b]
    Interface List
    0x1 ........................... MS TCP Loopback interface
    0x2 ...00 0f b0 3d bc 1d ...... Realtek RTL8139 Family PCI Fast Ethernet NIC - Packet Scheduler Miniport
    0x10004 ...00 02 72 1f 4a 81 ...... Bluetooth Device (Personal Area Network)
    Active Routes:
    Network Destination        Netmask          Gateway       Interface  Metric
    [B]          [COLOR="Red"][/COLOR]       20[/B]
       20       20
         20       1           10004       1
    [B]Default Gateway:[/B]
    The TCP setting tells you where the gateway is located and that is confirmed in the
    Routing Table as the Default Gateway: entry.
    Notice that the Network Destination is show as

    This means, if all else fails (aka, don't know where to send packets), send it here.

    Now as you add more NIC cards (or routers with other ISP connections), your system
    still has ONLY one default route. All that extra effort doesn't change the routing table
    and all your ethernet traffic STILL exit your system headed for the Default Route.

    Conclusion: You can not get extra "bandwidth" by adding more ISP connections.
  3. alanrwood

    alanrwood TS Rookie Topic Starter


    Many many thanks for your excellent and exhaustive response. I could not have asked for a better one. I had rather thought that it would not be possible so this just confirms the position. As there is no extra cost involved I will probably go ahead anyway to get both lines set up for ADSL but use one for if/when there is a problem on the other.

    I guess there must be some way of doing it which involves more complicated and expensive hardware as I keep reading the term "Load Sharing" and I am sure some businesses have this as a safety measure but it is probably not worth it to a home user such as myself. Pity though.

    Regards and thanks

  4. Cookie90

    Cookie90 TS Rookie

    A multi-wan router is a business solution. Handles several ADSL lines coming in and can load balance between them all. Normally this is done by % balance or per session.


    As for a multi router set-up that is also possible providing the supplier supports this. Cisco uses a system called PBR (Policy Based Routing).


    This summarized is where the switch decides which router the traffic should be routed to based on configuration (normally IP Address).

    But like you say for a home set-up this is pretty pointless.

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