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Forum Replies

  1. CAM: High speed memory that is primarily used for a switch’s layer 2 lookup information. This information allows the switch to decide which port to send a packet to (a known MAC address) or whether to flood it to all ports (unknown MAC address).

    TCAM: Not all switches have this. Think of this as an extension of CAM. It is used for very rapid decisions on ACLs and Quality of Service. On high end layer 3 switches, the TCAM can also contain the FIB, again, so specialized hardware can making routing decisions without interrupting the central CPU of the switch.

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  2. Thanks Rene,

    I have another question, in the above section where u have mention about ARP request construct, I think the behavior of switches are different

    The multilayer switch will check the routing table, notices that 192.168.20 /24 is directly connected and the following will happen:
    The destination MAC address changes from FFF (Multilayer switch Fa0/1 ) to BBB (ComputerB).
    The source MAC address changes from AAA (ComputerA) to GGG (Multilayer switch Fa0/2).===This seems to be Incorrect

    I LAB this up with 3 switches (all real hardware 3550/3560) [ c3560-ips

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  3. Hi Andrew!,

    Glad to see you around and yea! thanks for confirming my doubt.

    I have a few more doubts that i have no where to turn to and i hope you will enlightened me…

    My coreswitch has ip cef turn on my default.

    q1) I have been reading up abit on cisco about IP CEF and it seems like to enable/disable IP CEF, you have to do in at the ingress interface as the decision (e.g. load balance is done there). – is it right ?

    Assuming i have “no ip cef” and only wish to turn on ip cef on certain interfaces and ->
    q2) if i want to do to packet loadbalancing, should “ip

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    1. The ARP table is stored in RAM, and not in either CAM or TCAM

    2. Here is the Cisco definition of Epoch and how it is used:

    The term "epoch" refers to a period of time. A new epoch for a Cisco Express Forwarding table begins when a table rebuild is initiated. The time after this instant is in an epoch different from the time before, and the different epochs are numbered between 0 and 255. Through the use of epochs, the software can distinguish between old and new forwarding information in the same database structure and can retain the old Cisco Express Forwar
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