1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

ARP + Router startup

Discussion in 'General Cisco Certifications' started by baldie, Jul 27, 2006.

  1. baldie

    baldie Bit Poster

    12
    0
    2
    Morning all,

    Can someone please help me out....

    PC1 wants to get to PC 4 which is on a different subnet and needs to go through Router A, this is a brand spanking new network, i.e all Switch mac tables are blank.

    PC1 sends an ARP broadcast requesting Router A's mac address, Router A responds, PC 1 sends the packet (encapsulated in an Ethernet frame) to Router A with a Destination IP address of PC4.

    At what point does the MAC address table get updated, I know that when PC1 sends to PC4 it will update the table with its Source address, but does the ARP request and reply update the switch table?

    PLus..........one more thing.....

    To enter setup mode on a Router:

    Change the config register to 2142 to ignore NVRAM or tyoe "setup" from privilege Exec

    To Enter ROMMON mode

    Change the config register to 2100

    Thanks in advance.
     
  2. hbroomhall

    hbroomhall Petabyte Poster Gold Member

    6,623
    115
    224
    You need to be a little more specific - see below.
    Which MAC address table? There will be one each in PC1, PC4 and the router.
    What switch? Where is it located?

    The sending of the packet by PC1 effectively updates the MAC info on PC1 and the router. The sending of the packet by the router on to PC4 effectively updates both the router and PC4.

    Harry.
     
    Certifications: ECDL A+ Network+ i-Net+
    WIP: Server+
  3. baldie

    baldie Bit Poster

    12
    0
    2
    Sorry, when I say table I mean the MAC address table on the switch thats located between PC1 and the router (DG of PC1), if PC1 sends and ARP request for the MAC address of thr router does anything get added to the Switch's MAC address table during this process, or does it just get added (the source mac address of PC 1) when the frame is sent.
     
  4. hbroomhall

    hbroomhall Petabyte Poster Gold Member

    6,623
    115
    224
    If we assume that everybody's ARP tables are empty, and also any MAC address lists when we start, then when PC1 send it's ARP request to the router the switch will a) note the MAC address and port it received the packet for future use, and b) echo the packet to every other port.

    The reply from the router will then enable the switch to associate the router MAC with the port it arrived on.

    Harry.
     
    Certifications: ECDL A+ Network+ i-Net+
    WIP: Server+

Share This Page

Loading...