Configuring multiple routers?

Discussion in 'Home Networking' started by DaveC, Nov 5, 2012.

  1. DaveC

    DaveC Guest

    The Comcast service comes into a Motorola cable modem (SB6121). Plugged into
    the modem's Ethernet port was an Airport Extreme base station.

    This provided wifi service to this small office building for more than a

    Now there is a need for adding to that some Ethernet capability. (Yes, the
    Airport has Ethernet ports, but it is located high up where plugging in
    Ethernet cables is impractical.) So...

    I added a Netgear RP614v2 router, plugged it into the modem, and plugged the
    Airport into the Netgear router.

    Doing this killed the wifi. The Ethernet ports on the Netgear router now
    work, but no wifi. (Tried different ports on the Netgear, different cables;
    No joy. It's not the fault of the hardware.)

    I've spent many hours trying to configure the router and the Airport so as to
    bring back wifi. I presume I'm not making the right choices.

    Can someone point out the basic important points re. IP addresses? For
    example, the Airport configuration page says that my choices are: 1. share
    the WAN fixed IP address; 2. distribute IP addresses via DHCP; 3. nothing
    (bridge mode). Do I want the Airport to not distribute IP addresses (bridge
    mode) because the router will do that? And do I need to configure the modem's
    WAN IP address to match the modem's IP? Or does this happen automatically?

    A good reference to read about router configuration in general (IP addresses,
    DHCP, etc.) would be a great starting point. Suggestions?

    If there's a more-appropriate group in which to ask this, just say so.

    DaveC, Nov 5, 2012
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  2. DaveC

    Henry Law Guest

    This is hard to diagnose remotely and asynchronously. But it might help
    if I go through some of the basics of what used to work and how it might
    work now.

    The airport controlled the modem and provided multiple IP addresses to
    the LAN (both wired and wireless); it's likely therefore that it was
    acting as a DHCP server and passing out addresses to attached devices.
    I'm betting they were in the 192.168.1.x address range too. Upstream of
    it there was a single IP address on the Comcast network; the airport was
    probably doing NAT, so that all packets from attached devices looked as
    if they were coming from the single Comcast IP address.

    Now you've plugged in another router -- another layer of routing --
    betwen the existing Airport router and the modem. That router expects
    to be doing exactly what the Airport did -- DHCP, NAT and all that. And
    I'd bet it is also doing it in 192.168.1.x. So it's clear that what you
    have isn't going to work as it is.

    What I'd suggest is this:

    Configure the Netgear router as a DHCP server (almost certainly the
    default), and leave its address range as whatever it is set to (probably
    192.168.1.x, as I say). That should support the Ethernet ports.

    Plug the Airport into one of the Ethernet sockets and configure it in
    "Bridge mode", so that the network downstream of the Airport is the same
    as the Netgear's. You might need to give it a fixed IP address rather
    than have it get one via DHCP. If so, I suggest to get it
    out of the way of the ones allocated dynamically.

    With luck, a device connecting wirelessly to the Airport will get a DHCP
    address directly from Netgear and everything will go off with a roar.

    Without luck there's something I've overlooked and you'll be just as
    badly off as before. If that's the case, I'm sorry.
    Henry Law, Nov 5, 2012
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  3. DaveC

    Daniel James Guest

    It seems to me that you bought the wrong piece of kit ... all you needed
    to do was to purchase a network switch (a cheap, unmanaged switch) and
    connect it by means of single ethernet cable to one of the wired ports of
    your Airport. You would then have been able to connect further devices
    directly to the switch (which you could place in any convenient
    location). Everything else would have continued to work as before.

    With your current arrangement the Netgear router is managing a wired
    network, and the Airport attached to it is attempting to manage a
    different, subsidiary network. If you can configure the Airport so that
    its own router functions are disabled and it acts merely as a switch/WAP
    you may be able to get this working, but I don't think an Airport can be
    used in that way(?)
    Yes ... but you don't really need to mess with that stuff. Just use a
    switch instead of trying to make two routers play nicely together.
    I think any one of the three you chose should be fine.

    Daniel James, Nov 5, 2012
  4. DaveC

    DaveC Guest

    It seems to me that you bought the wrong piece of kit ... all you needed
    I first tried a switch connected directly to the modem. It didn't work, and I
    presume it was because the modem has one E port and did not provide NAT or
    DHCP function. That's why I went with a router.

    Modem data sheet:

    DaveC, Nov 5, 2012
  5. DaveC

    DaveC Guest

    Running another cable to the remote Airport location is not an option.
    DaveC, Nov 5, 2012
  6. DaveC

    Henry Law Guest

    Ah, but you connected it to the wrong place. As Messrs Gold and James
    have rightly said, if you'd connected the switch (with a cable long
    enough to reach down from the ceiling to somewhere more convenient) to
    one of the Ethernet ports on the Airport router (not into the modem) it
    would have provided whatever-number of "downstream" ports which are part
    of the original network. If you've still got that switch then that's a
    better option than perservering with your Netgear box, which you could
    then either sell or keep for some future use.

    To explain a little, in the hopes it will help you, the modem won't
    manage an Ethernet network: it doesn't know how. All it knows how to do
    is to connect to Comcast and reflect its IP address (an external one, in
    Comcast's network) onto a socket of some kind.

    The Airport tells the modem to connect (and usually provides userid and
    password and that sort of thing), and it has a router component which is
    responsible for managing a separate network (with a private address
    range) on its "downstream" side. In this case "managing" means handing
    out addresses via DHCP, doing NAT, providing firewall functions and so on.

    A switch is rather like a power strip; it plugs into one socket and then
    provides multiple sockets for other devices to plug into. It's passive
    (at this level of discussion at least): it doesn't do anything networky
    and doesn't understand what an IP address is. And it doesn't understand
    how to tell a modem what to do.
    Henry Law, Nov 5, 2012
  7. The Comcast cable modem must remain connected to the WAN port of the Airport
    Extreme Base station. Then connect one port of the switch to one of the LAN
    ports of the Airport Extreme (using a long enough cable to allow the switch
    to be placed it in a reachable location) and use the remaining ports of the
    switch for the extra Ethernet capability you require.
    Anthony R. Gold, Nov 5, 2012
  8. DaveC

    Henry Guest

    Actually, what you are describing is a hub, not a switch. A switch can
    be actively networky because it does differentiate amongst the IP
    addresses of the various devices attached to it in order to channel
    traffic to the correct machine, rather than send it along wholesale to
    all the sockets.
    Henry, Nov 5, 2012
  9. DaveC

    Henry Law Guest

    OK, in which case leave the Netgear unit in place and configure the
    Airport as a bridge. If it doesn't work then come back here; post the
    results of "ipconfig /all" from a PC wirelessly connected to the Airport
    (assuming you're Windows; otherwise "ifconfig" on linux. Should be
    possible to help you get on the air (sorry).
    Henry Law, Nov 5, 2012
  10. I don't know the Airport Extreme but as far as I can tell it is
    Apple's wireless router and should perform just like any other.

    My Lady Friend has two wireless routers on her home network, because
    her old one only supports WEP and while her and her room-mate's older
    laptops worked with it, both have new work laptops as well that don't
    support WEP (as configured by security admins) so she got a modern
    router that wouldn't support WEP.

    I forget which one is connected to the cable modem, with the other
    connected to the first one via an Ethernet cable.

    But the setup works. The two routers have been given different names
    and passwords, and have different default IP addresses.

    That's all I can think of.

    I understand why the original poster doesn't want keep plugging cables
    somewhere not easily accessible, but running a single cable either to
    a switch (I do that) or a second router shouldn't be a problem because
    that's where subsequent cabling will be.

    It's simply a case of set it and forget it for the first cable, all
    the others connect to the switch.
    Christopher A. Lee, Nov 5, 2012
  11. DaveC

    DaveC Guest

    Well I've failed.

    No matter what I try (and I've tried all suggestions made here) I get this:
    in the Netgear RP614v2's connected devices table, a directly-connected iMac
    shows up, but not the Airport Extreme (in bridge mode). (Yes I power-cycled
    and refreshed the table after each new configuration.)

    I've tried connecting the AE to several different ports on the Netgear, first
    confirmed by plugging in the iMac.

    Cables are not the issue because if I plug the AE (in non-bridge mode) into
    the cable modem (using the same or a different cable), it works.

    I'm telling mgmt. that paying to have a 2nd cable run to the Airport (costly)
    is the solution. I don't like it but there it is.

    I wish I knew enough about the whole IP configuration thing to be able to
    point to something and say "That is at fault", but it's all a foggy mess (in
    my head). I know that with experience comes competence, but isn't there a
    good starting point such as a web-seminar or e-book that can cover the basics
    and more?

    Thanks for all who contributed to the discussion.

    DaveC, Nov 6, 2012
  12. DaveC

    Daniel James Guest

    Indeed ... but I think, perhaps, that unnecessary detail is what Henry
    Law was noting had been omitted when he wrote "at this level of
    discussion at least".

    OP clearly doesn't know a lot about networks and the difference between
    a hub and a switch really doesn't matter to him.

    Daniel James, Nov 6, 2012
  13. DaveC

    Daniel James Guest

    Really? As I read your original question you had already tried an
    arrangement with your Netgear router that would have required such a
    cable -- maybe I misunderstood.

    Just to be clear: What you would need is:

    Comcast modem -- (CAT5) -- Airport -- (CAT5)-- Switch
    Other device

    where (CAT5) indicates an ethernet cable (you'd need to power the
    devices as well, of course).

    What I thought you had said you had done was:

    Comcast modem -- (CAT5) -- Router -- (CAT5)-- Airport
    Other device

    I did read the part where you said that the Airport was positioned high
    up so plugging in Ethernet cables was impractical (and I assumed,
    perhaps wrongly, that the Comcast modem was in the same place) .. so in
    either case there would need to be one CAT5 cable running from that
    inaccessible place to the desktop (or wherever) that the ethernet ports
    are required.

    However, if the Airport is really inaccessible (even for installation of
    new kit) and you can't run even one cable from it ... the best option
    may be to leave all your existing kit where it was and install (on your
    desk, or elsewhere) a box that connects as a client to your existing
    WiFi (from the Airport) and provides wired ethernet connectivity for
    other devices. This connection will only operate at wireless speeds, of

    I *think* such boxes are called "wireless bridges" -- they do basically
    the same job as a Wireless Access Point but in reverse. You cannot use
    your Netgear RP614v2 router to do this, but I believe some of Netgear's
    WAP devices can be used as either end of a bridge connection (that is:
    to connect to another WAP to form a bridged network). Setting up a
    bridge is rather more complex than simply plugging a switch into the
    airport and how you set it up will depend on the kit you're using.

    Daniel James, Nov 6, 2012
  14. DaveC

    Rob Morley Guest

    Actually, what you are describing is a hub, not a switch. A switch can
    be actively networky because it does differentiate amongst the IP
    addresses of the various devices attached to it in order to channel
    traffic to the correct machine, rather than send it along wholesale to
    all the sockets.[/QUOTE]

    Actually the term "hub" is simply a topological description. Also
    you seem to be confusing the Layer 2 use of MAC to route packets via
    the appropriate port, with Layer 3 switches that are IP aware and use
    Rob Morley, Nov 6, 2012
  15. DaveC

    Pen Guest

    Perhaps this article at Gibson Research about multiple
    routers will help you understand.
    Pen, Nov 6, 2012
  16. DaveC

    DaveC Guest

    DaveC, Nov 6, 2012
  17. DaveC

    Henry Guest

    Actually pieces of hardware sold in the marketplace for many years,
    although nowadays largely supplanted by ... switches.
    Henry, Nov 6, 2012
  18. DaveC

    Rob Morley Guest

    Actually pieces of hardware sold in the marketplace for many years,
    although nowadays largely supplanted by ... switches.[/QUOTE]

    The switch, short for "switching hub", sharing its topology but not
    mode of operation with what is sometimes known as a "dumb hub" (for its
    inability to perform low level routing to appropriate ports).
    Rob Morley, Nov 6, 2012
  19. His original request said it killed the wi-fi but the cabled Ethernet

    So that would be the obvious place to start.

    Give the two routers different SSID names and passwords. That way
    there should be no possibility of their wireless interfering with each

    Also different IP addresses eg and - even if
    this isn't necessary it will make it easier to see what is connected
    to what.

    The second router's WAN will be its connection to the first router.

    The first router's WAN will be the cable modem and broadband

    My Lady Friend's home network is set up this way using an older
    802-11G router that supports WEP for her and her room-mate's home
    laptops, and a newer 802-11N (150Mbps) router for their work laptops
    which have been configured by their employers not to allow WEP.
    Christopher A. Lee, Nov 6, 2012
  20. DaveC

    Char Jackson Guest

    I'm off this afternoon. Where do you live? :)
    We could knock this out in no time.
    Char Jackson, Nov 6, 2012
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