Do you really need a router?

By Duck ยท 5 replies
Oct 23, 2006
  1. Hi, I have a Linksys ADSL modem with 1 USB port and 1 Ethernet port on the back. Can I connect a switch to the ethernet port to allow many more PCs to connect to the internet? If I can then why do some people have a router between the modem and the switch? What does it do?
  2. jobeard

    jobeard TS Ambassador Posts: 11,126   +982

    a very typical setup would be
    modem --- (wan side) router (lan side)--- one or more systems
    you can use a switch in place of the router *IF*
    • you don't want NAT/SPI services
    • you like to perform the setup yourself

    you would be wise to always use a router even if there's only one system
    attached, so as to have NAT and SPI features to protect you.

    a router also provides DHCP service so that your LAN systems can automatically be configured, which a switch can no provide

    frankly, I have this setup
    modem --- (wan side) router (lan side)--- two systems
                             a switch
                                   + ---- two more systems
    but this is strickly because I already had the switch AND it facilitated
    the physical wiring. Notice the switch is on the LAN side and all systems
    get NAT/SPI protection AND DHCP configuration services.

    NAT: Network Address Translation
    The public Internet is on the WAN side and your systems are on them LAN side.

    This forces the router to perform tricks (which a switch or hub can not do) to ensure your LAN addresses can reach outbound but the hackers can not reach inbound.

    SPI: Statefull Packet Inspection
    Statefull says there is a specific sequence of events and a valid data stream
    always starts in a well know condition; any data that has not started from that
    condition is *known* to be bogus and the packet is discarded.
    this is a very effective anti-virus, anti-trojan tool!

    Conclusion: in my opinion, every hispeed broadband should be required to have a router immediatel attached to the modem.
  3. Nodsu

    Nodsu TS Rookie Posts: 5,837   +6

    There is really no technical reason why it wouldn't work.. But there are many commercial reasons :)

    A hub/switch does not usually work for sharing DSL because:
    a) your ISP wants you to establish a PPPoE connection (you have a username and a password for that) to get an internet connection. Your ISP allows only a single login per username.
    b) your ISP will give you only one IP address. You need a routing device to share an IP.

    If you have a very open-minded and a naive ISP, then a hub/switch may work (technically) - all your PCs would automagically get an IP via DHCP with no authentication required.
  4. Duck

    Duck TS Rookie Topic Starter Posts: 16

    Thanks very much for that detailed reply, jobeard. I think I have NAT already because my IP address is and that IP address would not be visible from the internet side. Having a firewall would be good so I will probably get a router even for just 1 PC like you said.

    Nodsu, if I understand you correctly, I'm not trying to connect the switch to the internet. I was going to go Internet >> Modem >> Switch. So the Modem was like a gateway.
  5. jobeard

    jobeard TS Ambassador Posts: 11,126   +982

    yes and no. it is the only PATH, but does not provide 'gateway services'.

    go to your 'router address' via your browsed http://192.168.01./
    and verify the settings. you should see DHCP enabled and a PUBLIC IP address
    for the WAN that is not 192.168.*.*

    if so, then your modem has a router feature built-in and the switch would work,
    just no SPI.
  6. Duck

    Duck TS Rookie Topic Starter Posts: 16

    ahh that makes sence. I didnt realize my modem had a router built in. Thanks for your help.
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