How can you minimize unicast flooding in a network?

How can you minimize unicast flooding in a network?
A. Set the router’s ARP timeout value to less than the timeout value for Layer 2 forwarding table entries.
B. Set the router’s ARP timeout value to be the same as timeout value for Layer 2 forwarding table entries.
C. Configure HSRP on two routers, with one subnet preferred on the first router and a different subnet preferred on the second router.
D. Set the router’s ARP timeout value to greater than the timeout value for Layer 2 forwarding table entries.

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4 thoughts on “How can you minimize unicast flooding in a network?

  1. So which is it. Replies by Anonymouse says L2 timeout should be greater than IP arp timeout. Others say the opposite? Which is it?

  2. A and B can ce correct;

    In order to prevent unicast flooding, you should set your CAM aging timer to be greater than or equal to the ARP timeout value.
    The default value for the L3 switch ARP timeout is 4 hours, and the default time for the L2 switch timeout is 300 seconds (5 minutes). To prevent unicast flooding, the L2 switch CAM aging timeout should be set to a value greater than the ARP timeout of the L3 switch.
    You can use one of the following commands in order to increase the CAM aging timer for the affected VLAN to match the ARP aging time:
     If you are using CatOS, use the set cam agingtime command to change the CAM aging timer.
     If you are using Cisco IOS software, use the mac−address−table aging−time command to change the CAM aging timer.

  3. I think correct is B.
    Here https://www.cisco.com/c/en/us/support/docs/switches/catalyst-g-l3-series-switches/14975-47.html

    This is because the ARP aging time is 4 hours by default, significantly longer than the bridge table aging time.

    There are two workarounds for this problem:

    Redesign the routing topology so that traffic for a given remote IP subnet follows the same route into and out of the Catalyst 2948G-L3 switch.

    Reduce the ARP aging time on router interfaces connected to the Catalyst 2948G-L3 switch to 5 minutes (with the arp timeout interface configuration command). and CAM table, by default is 300 second=5minutes.

    SO, the best answer is EQUAL. ‘A’ question tell us that it must be less, not equal or less. As minimum it must be EQUAL and only after less. So “B”.

  4. A

    https://www.cisco.com/c/dam/en/us/td/docs/video/headend/Digital/QAM_Series/4022934_A.pdf

    LAN switches use forwarding tables, such as Layer 2 and Content Addressable
    Memory (CAM) tables, to direct traffic to specific ports based on the virtual LAN
    (VLAN) number and the destination MAC address of the frame.

    In order to prevent unicast flooding, you should set your CAM aging timer to be
    greater than or equal to the ARP timeout value.
    The default value for the L3 switch ARP timeout is 4 hours, and the default time for
    the L2 switch timeout is 300 seconds (5 minutes). To prevent unicast flooding, the L2
    switch CAM aging timeout should be set to a value greater than the ARP timeout of
    the L3 switch.

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