+ Reply to Thread
Results 1 to 4 of 4
  1. Member
    Join Date
    Sep 2006
    Location
    London, UK
    Posts
    37

    Certifications
    A+, N+, 5 x MCP, CCNA, BCMSN, working on BSCI
    #1

    Default Layer 3 Switching/ CEF confusion

    Hi All

    Question to those taking or have done the BCMSN, or who have access to a 3550 EMI switch.

    I'm looking at Multilayer switching, particularly the CEF variety and am confused. The Sybex book I am using says that to CEF is the L3 switching method on 3550 switches, and to enable it you use;

    conf t
    ip routing
    ip cef

    You then have to convert the L2 interface to L3 by using the command 'No switchport'. CEF is then enabled on this switch.

    But if you do not enter 'ip cef' does this mean that the 3550 will not route packets? I understand that 'ip routing' has to be enabled, but wasn't aware that the cef command had to be carried out too. Additionally, what interface are you converting to L3? The one that is connected to a L2 switch in a 'router on a stick' capacity?

    Confused!
    Reply With Quote Quote  

  2. SS
  3. Senior Member keenon's Avatar
    Join Date
    Jun 2004
    Location
    TN
    Posts
    1,915

    Certifications
    CCIE R/S
    #2

    Default Re: Layer 3 Switching/ CEF confusion

    Quote Originally Posted by Dilan77
    Hi All

    Question to those taking or have done the BCMSN, or who have access to a 3550 EMI switch.

    I'm looking at Multilayer switching, particularly the CEF variety and am confused. The Sybex book I am using says that to CEF is the L3 switching method on 3550 switches, and to enable it you use;

    conf t
    ip routing
    ip cef

    You then have to convert the L2 interface to L3 by using the command 'No switchport'. CEF is then enabled on this switch.

    But if you do not enter 'ip cef' does this mean that the 3550 will not route packets? I understand that 'ip routing' has to be enabled, but wasn't aware that the cef command had to be carried out too. Additionally, what interface are you converting to L3? The one that is connected to a L2 switch in a 'router on a stick' capacity?

    Confused!
    i'll try to best answer

    when you want to make a L3 switch route packets "no switchport" command needs to be entered. additionally an ip address must be assigned to that interface ( just like a router) the routing for the vlans connected to this switch would be routed from the "Interface Vlan # , with an ip address

    ip routing has to be turned on to route packets CEF just makes it more effective/faster in short.. you should do a lookup on cisco site for cef
    Reply With Quote Quote  

  4. MrD
    MrD is offline
    Senior Member MrD's Avatar
    Join Date
    Feb 2006
    Location
    Nashville, TN
    Posts
    447

    Certifications
    CCIE#20217, CCNP, CCDP, BS MIS
    #3
    Reply With Quote Quote  

  5. Member
    Join Date
    Sep 2006
    Location
    London, UK
    Posts
    37

    Certifications
    A+, N+, 5 x MCP, CCNA, BCMSN, working on BSCI
    #4
    Brilliant, thanks guys....
    Reply With Quote Quote  

+ Reply to Thread

Social Networking & Bookmarks