Cef

DevilWAHDevilWAH The Bringer of LightMember Posts: 2,997 ■■■■■■■■□□
CEF

I have a question about cef,

supposing I have a 3750, that does not have any active vlan interfaces. But does have separate VLANS set up. It is trunked to a second switch/router that is doing the routing between the vlans.

So all routing is done off the switch, does the fact that the 3750 is running cef make any difference to the network.

what I am wondering is is there any way for the switch to learn/ be told by the router. that station x on vlan y is on port z and station a on vlan b is on port C

and that if data need to pass between station x and station a, this can be achived with out (all) the packets in the conversation having to travel across the trunk to the router.

I jsut head a comment that not all multilayer switch are layer 3 switchs, but all layer 3 switch are multilayer switch. And I was wondering what do you use a non layer 3 multilayer switch for.

CEF on a single switch/router (or routers with routing between them) makes perfect seance. just I don't get how cef affects non routing devices.

Cheers
  • If you can't explain it simply, you don't understand it well enough. Albert Einstein
  • An arrow can only be shot by pulling it backward. So when life is dragging you back with difficulties. It means that its going to launch you into something great. So just focus and keep aiming.

Comments

  • DevilWAHDevilWAH The Bringer of Light Member Posts: 2,997 ■■■■■■■■□□
    ColbyG wrote: »
    CEF is L3.


    see that what i thought, but a 2950 switch can run cef and that is not a layer 3 switch ?

    And I remember reading that you can without enabling routing on a layer 3 switch use it to incress routing throughput by allowing direct forwarding of traffic between vlans with out the need for all packets in a conversation to be sent to the router.
    • If you can't explain it simply, you don't understand it well enough. Albert Einstein
    • An arrow can only be shot by pulling it backward. So when life is dragging you back with difficulties. It means that its going to launch you into something great. So just focus and keep aiming.
  • Forsaken_GAForsaken_GA Senior Member Member Posts: 4,024
    DevilWAH wrote: »
    see that what i thought, but a 2950 switch can run cef and that is not a layer 3 switch ?

    Where did you get that from? That's not what I see

    cisco WS-C2950T-24 (RC32300) processor (revision P0) with 19912K bytes of memory.
    Last reset from system-reset
    Running Enhanced Image

    switch001(config)#ip ?
    Global IP configuration subcommands:
    access-list Named access-list
    accounting-list Select hosts for which IP accounting information is kept
    accounting-threshold Sets the maximum number of accounting entries
    accounting-transits Sets the maximum number of transit entries
    alias Alias an IP address to a TCP port
    default-gateway Specify default gateway (if not routing IP)
  • Forsaken_GAForsaken_GA Senior Member Member Posts: 4,024
    DevilWAH wrote: »
    And I remember reading that you can without enabling routing on a layer 3 switch use it to incress routing throughput by allowing direct forwarding of traffic between vlans with out the need for all packets in a conversation to be sent to the router.

    This is also not correct, cef requires IP routing to be running.

    From a 3550:

    SW4#sh ip cef
    %IPv4 CEF not running
    SW4#config t
    Enter configuration commands, one per line. End with CNTL/Z.
    SW4(config)#ip cef
    %Must enable ip routing first
  • DevilWAHDevilWAH The Bringer of Light Member Posts: 2,997 ■■■■■■■■□□
    yer it was from a network engineer in a network consultancy company!!

    he was going on about running a set up like router on a stick. where the routing was done on the layer 3 router, but the switch could learn the routes and send packets direct across vlans. with out them needing to travel the trunk to the router.

    It did seem a bit to good to be true...

    as for the 2950 I have never used one in my life the idea they can run cef was what I was told and have read on internet (since first post been looking around and notice none of it was cisco documentation).... I started with 3550's and have moved up, so been a bit spoilt as far as layer 3 switch go.
    • If you can't explain it simply, you don't understand it well enough. Albert Einstein
    • An arrow can only be shot by pulling it backward. So when life is dragging you back with difficulties. It means that its going to launch you into something great. So just focus and keep aiming.
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