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Router to PC connection?

Discussion in 'Routing & Switching' started by flopstocks, May 11, 2007.

  1. flopstocks

    flopstocks Nibble Poster

    After studying section 5.1.5 (UTP Implementation) I see that to connect a PC to a router a crossover cable should be used? I know for a fact that on my home nework a straight though cable is being used. Do the SOHO routers differ from CISCO ones? Or is this a mistake?
    Certifications: A+, Network+, CCNA, BSc(Hons) Open
  2. Mikel

    Mikel New Member

    You are right, it should be a crossover cable from a router to a pc. However if the the port you are connecting to on the router has an X beside it, it indicates that the router has already crossed over the pins it receives on meaning a straight through cable can be used.
    WIP: CCNA, Computer Networking Bsc
  3. hbroomhall

    hbroomhall Petabyte Poster Gold Member

    In addition, many home routers include a switch. Now a PC to a switch would use a non-crossed cable.

    Finaly, many home pieces of kit have auto-switching on the sockets, which means that for home users cross-over cables are mostly a thing of the past.

    Certifications: ECDL A+ Network+ i-Net+
    WIP: Server+
  4. r.h.lee

    r.h.lee Gigabyte Poster

    That is correct. Here's how I remember which type of cable to use. If there is 1 OSI layer difference, then a straight through cable should be used. For example, from a PC (Layer 1) to switch (Layer 2) or switch (Layer 2) to router (Layer 3). If there is 0 or 2 OSI layer difference, then a crossover cable. For example, from a PC (Layer 1) to PC (Layer 1), switch (Layer 2) to switch (Layer 2), or PC (layer 1) to router (Layer 3).

    That depends on the router, either SOHO or Cisco. That's because some routers have a built-in switch for the LAN side. So since there is 1 OSI layer difference, PC (Layer 1) to built-in switch (Layer 2), it is correct to use a straight through cable.

    No, it is not a mistake. When you connect a PC (Layer 1) to a Cisco Fast/Ethernet port (Layer 3), you are connecting the PC to a router port, not a switch port. In the case of the SOHO router, you're connecting the PC (Layer 1) to the built-in switch (Layer 2) so in that case you use a straight through cable.

    I hope this helps.
    Certifications: MCSE, MCP+I, MCP, CCNA, A+
  5. garyb

    garyb Byte Poster

    I found this to be true also. On my SonicWALL firewall, SonicWALL tech support absolutely insist that I use a crossover cable from firewall LAN port to LAN switch port, yet for the last 18 months I have used a normal ethernet cable which operates OK. Not sure what to make of it !:x


    WIP: MCSA 2003
  6. NetEyeBall

    NetEyeBall Kilobyte Poster

    Cool way to remember it Lee! Never thought of it like that.
    Certifications: CCNA, A+, N+, MCSE 4.0, CCA
    WIP: CCDA, CCNP, Cisco Firewall
  7. flopstocks

    flopstocks Nibble Poster

    Yea thanks mate, that should really help me!
    Certifications: A+, Network+, CCNA, BSc(Hons) Open
  8. jackson

    jackson New Member

    Absolutly correct, it is for ease of use, manufacturer deploy this auto-detect and switching mechanism for most of the switches and routers nowaday.

    More to say on cabling, RJ45 have divided into 2 cat. MDI and MDI-X
    MDI: Wire 1 and wire 2 for data transmission, wire 3 and wire 6 for data reception:
    Router Port
    Network card Port
    Switch uplink Port
    Hub uplink Port

    MDI-X: Wire 1 and wire 2 for data reception, wire 3 and wire 6 for data transmission:
    Switch Port
    Hub Port

    Required cabling method is to use a straight-through cable to connect two ports only when one port is designated with an X. Use a crossover cable to connect two ports when both ports are designated with an X or when both ports do not have an X

    For Cisco, it also have catch up with this world, please refer to the Official Cisco link,

    Pay special attention to the following paragraph.
    You can use the mdix auto interface configuration command in the CLI to enable the automatic medium-dependent interface crossover (auto-MDIX) feature. When the auto-MDIX feature is enabled, the switch detects the required cable type for copper Ethernet connections and configures the interfaces accordingly. Therefore, you can use either a crossover or a straight-through cable for connections to a copper 10/100, 10/100/1000, or 1000BASE-T SFP module port on the switch, regardless of the type of device on the other end of the connection.

    The auto-MDIX feature is enabled by default on switches running Cisco IOS Release 12.2(18 ) SE or later. For releases between Cisco IOS Release 12.1(14) EA1 and 12.2(18 ) SE, the auto-MDIX feature is disabled by default. For configuration information for this feature, see the switch software configuration guide or the switch command reference.

    for more information, you can search "mdi-x" in cisco official site.

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