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  1. 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-ipservicesk9-mz.122-55.SE10/ c3550-ipservicesk9-mz.122-44.SE6]

    Simple topology- SW is just acting as regular sw with fa 0/23 & 19 as access port, SW2 and SW3 are acting like a end host (sort of PC with IP address on them)

    SW2 -----------{fa 0/23 on both end}----------------SW1-----------{fa 0/19 on both end}-----------------SW3

    When ARP request is created by SW2, its destination is always SW1 fa 0/19 and NOT fa 0/23 on SW1!, I also took packet capture and its shows the same thing,

    Here is the relevant data, I will appreciate if you can review the config and attached screen shot and advise, Thanks Gary

    ------------------------------------------------------------------------------

    SW1#sh int status | inc 0/19|0/23          
    Fa0/19                       connected    1          a-full  a-100 10/100BaseTX
    Fa0/23                       connected    1          a-full  a-100 10/100BaseTX
    
    SW1#sh cdp nei
    Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
                      S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone, 
                      D - Remote, C - CVTA, M - Two-port Mac Relay 
    
    Device ID        Local Intrfce     Holdtme    Capability  Platform  Port ID
    SW2              Fas 0/23          146             R S I  WS-C3560- Fas 0/23
    SW3              Fas 0/19          128             R S I  WS-C3550- Fas 0/19
    

    !!! Before PING, SW1 MAC table don’t have any dynamic entry!!!

    SW1#sh mac address-table 
              Mac Address Table
    -------------------------------------------
    
    Vlan    Mac Address       Type        Ports
    ----    -----------       --------    -----
     All    0100.0ccc.cccc    STATIC      CPU
     All    0100.0ccc.cccd    STATIC      CPU
     All    0180.c200.0000    STATIC      CPU
     All    0180.c200.0001    STATIC      CPU
     All    0180.c200.0002    STATIC      CPU
     All    0180.c200.0003    STATIC      CPU
     All    0180.c200.0004    STATIC      CPU
     All    0180.c200.0005    STATIC      CPU
     All    0180.c200.0006    STATIC      CPU
     All    0180.c200.0007    STATIC      CPU
     All    0180.c200.0008    STATIC      CPU
     All    0180.c200.0009    STATIC      CPU
     All    0180.c200.000a    STATIC      CPU
     All    0180.c200.000b    STATIC      CPU
     All    0180.c200.000c    STATIC      CPU
     All    0180.c200.000d    STATIC      CPU
     All    0180.c200.000e    STATIC      CPU
     All    0180.c200.000f    STATIC      CPU
     All    0180.c200.0010    STATIC      CPU
     All    ffff.ffff.ffff    STATIC      CPU
       1    0015.2b95.4c00    DYNAMIC     Fa0/19
       1    0023.05c6.b6c1    DYNAMIC     Fa0/23
    Total Mac Addresses for this criterion: 22
    
    SW2#sh run int fa 0/23
    Building configuration...
    
    Current configuration : 86 bytes
    !
    interface FastEthernet0/23
     no switchport
     ip address 10.10.12.2 255.255.255.0
    end
    

    !!! Before PING, SW2 MAC table don’t have any dynamic entry!!!

    SW2#sh mac address-table 
              Mac Address Table
    -------------------------------------------
    
    Vlan    Mac Address       Type        Ports
    ----    -----------       --------    -----
     All    0100.0ccc.cccc    STATIC      CPU
     All    0100.0ccc.cccd    STATIC      CPU
     All    0180.c200.0000    STATIC      CPU
     All    0180.c200.0001    STATIC      CPU
     All    0180.c200.0002    STATIC      CPU
     All    0180.c200.0003    STATIC      CPU
     All    0180.c200.0004    STATIC      CPU
     All    0180.c200.0005    STATIC      CPU
     All    0180.c200.0006    STATIC      CPU
     All    0180.c200.0007    STATIC      CPU
     All    0180.c200.0008    STATIC      CPU
     All    0180.c200.0009    STATIC      CPU
     All    0180.c200.000a    STATIC      CPU
     All    0180.c200.000b    STATIC      CPU
     All    0180.c200.000c    STATIC      CPU
     All    0180.c200.000d    STATIC      CPU
     All    0180.c200.000e    STATIC      CPU
     All    0180.c200.000f    STATIC      CPU
     All    0180.c200.0010    STATIC      CPU
     All    ffff.ffff.ffff    STATIC      CPU
    Total Mac Addresses for this criterion: 20
    
    SW3#sh run int fa 0/19
    Building configuration...
    
    Current configuration : 86 bytes
    !
    interface FastEthernet0/19
     no switchport
     ip address 10.10.12.3 255.255.255.0
    end
    

    !!! Before PING, SW3 MAC table don’t have any dynamic entry!!!

    SW3#sh mac address-table 
              Mac Address Table
    -------------------------------------------
    
    Vlan    Mac Address       Type        Ports
    ----    -----------       --------    -----
     All    0015.2b95.4c00    STATIC      CPU
     All    0015.2b95.4c01    STATIC      CPU
     All    0015.2b95.4c02    STATIC      CPU
     All    0015.2b95.4c03    STATIC      CPU
     All    0015.2b95.4c04    STATIC      CPU
     All    0015.2b95.4c05    STATIC      CPU
     All    0015.2b95.4c06    STATIC      CPU
     All    0015.2b95.4c07    STATIC      CPU
     All    0015.2b95.4c08    STATIC      CPU
     All    0015.2b95.4c09    STATIC      CPU
     All    0015.2b95.4c0a    STATIC      CPU
     All    0015.2b95.4c0b    STATIC      CPU
     All    0015.2b95.4c0c    STATIC      CPU
     All    0015.2b95.4c0d    STATIC      CPU
     All    0015.2b95.4c0e    STATIC      CPU
     All    0015.2b95.4c0f    STATIC      CPU
     All    0015.2b95.4c10    STATIC      CPU
     All    0015.2b95.4c11    STATIC      CPU
     All    0015.2b95.4c12    STATIC      CPU
     All    0015.2b95.4c13    STATIC      CPU
     All    0015.2b95.4c14    STATIC      CPU
     All    0015.2b95.4c15    STATIC      CPU
     All    0015.2b95.4c16    STATIC      CPU
     All    0015.2b95.4c17    STATIC      CPU
     All    0015.2b95.4c18    STATIC      CPU
     All    0015.2b95.4c19    STATIC      CPU
     All    0015.2b95.4c1a    STATIC      CPU
     All    0100.0c00.0000    STATIC      CPU
     All    0100.0ccc.cccc    STATIC      CPU
     All    0100.0ccc.cccd    STATIC      CPU
     All    0100.0ccd.cdce    STATIC      CPU
     All    0180.c200.0000    STATIC      CPU
     All    0180.c200.0001    STATIC      CPU
     All    0180.c200.0002    STATIC      CPU
     All    0180.c200.0003    STATIC      CPU
     All    0180.c200.0004    STATIC      CPU
     All    0180.c200.0005    STATIC      CPU
     All    0180.c200.0006    STATIC      CPU
     All    0180.c200.0007    STATIC      CPU
     All    0180.c200.0008    STATIC      CPU
     All    0180.c200.0009    STATIC      CPU
     All    0180.c200.000a    STATIC      CPU
     All    0180.c200.000b    STATIC      CPU
     All    0180.c200.000c    STATIC      CPU
     All    0180.c200.000d    STATIC      CPU
     All    0180.c200.000e    STATIC      CPU
     All    0180.c200.000f    STATIC      CPU
     All    0180.c200.0010    STATIC      CPU
    Total Mac Addresses for this criterion: 48
    
    SW2#sh int fa 0/23
    FastEthernet0/23 is up, line protocol is up (connected) 
      Hardware is Fast Ethernet, address is 0023.05c6.b6c1 (bia 0023.05c6.b6c1)
      Internet address is 10.10.12.2/24
    
    SW1#sh int fa 0/19       
    FastEthernet0/19 is up, line protocol is up (connected) 
      Hardware is Fast Ethernet, address is 0023.05cb.2815 (bia 0023.05cb.2815)
    
    SW1#sh int fa 0/23
    FastEthernet0/23 is up, line protocol is up (connected) 
      Hardware is Fast Ethernet, address is 0023.05cb.2819 (bia 0023.05cb.2819)
    
    SW3#sh int fa 0/19
    FastEthernet0/19 is up, line protocol is up (connected) 
      Hardware is Fast Ethernet, address is 0015.2b95.4c00 (bia 0015.2b95.4c00)
      Internet address is 10.10.12.3/24
    

    !!! AFTER PING, SW1 MAC table now having dynamic entry and notice the MAC address is of SW2 and SW3!!!

    SW1#sh mac address-table 
              Mac Address Table
    -------------------------------------------
    
    Vlan    Mac Address       Type        Ports
    ----    -----------       --------    -----
     All    0100.0ccc.cccc    STATIC      CPU
     All    0100.0ccc.cccd    STATIC      CPU
     All    0180.c200.0000    STATIC      CPU
     All    0180.c200.0001    STATIC      CPU
     All    0180.c200.0002    STATIC      CPU
     All    0180.c200.0003    STATIC      CPU
     All    0180.c200.0004    STATIC      CPU
     All    0180.c200.0005    STATIC      CPU
     All    0180.c200.0006    STATIC      CPU
     All    0180.c200.0007    STATIC      CPU
     All    0180.c200.0008    STATIC      CPU
     All    0180.c200.0009    STATIC      CPU
     All    0180.c200.000a    STATIC      CPU
     All    0180.c200.000b    STATIC      CPU
     All    0180.c200.000c    STATIC      CPU
     All    0180.c200.000d    STATIC      CPU
     All    0180.c200.000e    STATIC      CPU
     All    0180.c200.000f    STATIC      CPU
     All    0180.c200.0010    STATIC      CPU
     All    ffff.ffff.ffff    STATIC      CPU
       1    0015.2b95.4c00    DYNAMIC     Fa0/19 -----!!!!!This is MAC of 0/19 on sw3
       1    0023.05c6.b6c1    DYNAMIC     Fa0/23-----!!!!!This is MAC of 0/23 on sw2
    Total Mac Addresses for this criterion: 22
    
  2. 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 load-share per packet” command be issue on the ingress interface as well ?

    q3) Reading How to Verify Cisco Express Forwarding -> “http://www.cisco.com/c/en/us/support/docs/ios-nx-os-software/ios-software-releases-120-mainline/47205-cef-whichpath.html

    Use the show interface x/x stat command and determine the number of packets and bytes that the router forwarded through "Processor" instead of "Route cache." Note that "Route cache" includes both fast-switched and CEF-switched packets.
    router#show interface stats     
    FastEthernet0/0           
    Switching path Pkts In  Chars In Pkts Out Chars Out 
    Processor 95084 26211621 33493 3386174 
    Route cache 24581 1132797 24542 13297583 
    Distributed cache 0 0 0 0 
    Total  119665 27344418 58035 16683757
    

    Should this command be issue on the ingress or egress interface ?
    if it is to be issue on the INGRESS interface -> What does the “Pkts Outs” under Route cache means then ?

    Really hope to hear from you soon.

    Regards,
    Alan

    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 Forwarding database table while the software builds a new table. This is called epoch tracking and it allows Cisco Express Forwarding forwarding to continue uninterrupted while new Cisco Express Forwarding tables are being constructed, and it makes possible a seamless switchover when the new table becomes active

    When you issue a show ip cef <route>, the dependencies output means how many other routes depend (are resolvable through) the <route> you looked up via the CEF command.

  3. Hello Chandrakant.

    I believe you are correct. Actually, those two commands should be on for each of the R1 and R2 routers like so:

    R2(config)#ip route 3.3.3.0 255.255.255.0 192.168.23.3

    R1(config)#ip route 192.168.23.0 255.255.255.0 192.168.12.2

    I will let Rene know so it can be corrected.

    Thanks very much!

    Laz

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