Redundant link between to L3 switches

Discussion in 'Cisco' started by John, Nov 24, 2008.

  1. John

    John Guest


    I have two 12 miles distant offices. Cisco 3750 L3 switch on each side
    are connected via private PTP 1Gbs fiber link. Recently my company
    installed private PTP wireless backup link in case that fiber gets
    cut. Please note that wireless link should be up at all the time on
    standby and kick in when fiber goes down. I should be able to ping or
    access wireless unit’s (Motorola OS-Gemini) via its IP address when it
    is in standby mode. Reason for this is just to test it from time to
    My understanding is that there is two way to achieve this EIGRP (L3)
    or STP (L2). Can someone can help me decided which way to go and cons
    and pros of both ways
    Thank you very much
    John, Nov 24, 2008
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  2. John

    Trendkill Guest

    If you absolutely must have the same L3 networks available in both
    locations, then you don't really have a lot of choice. However this
    creates long convergence times (spanning-tree), and requires a lot of
    maintenance. I would generally avoid this at all costs unless you
    have specific requirements. Using a nice L3 design with a summarized
    address space and two links is much cleaner and much faster in terms
    of failover. While neither solution may work completely
    uninterrupted, a OSPF or EIGRP solution could easily reconverge while
    only needing to re-establish application sessions. Bring both links
    up in eigrp, eigrp will automatically prefer the higher bandwidth
    path, and if/when it fails, it will route over the backup path. Just
    ensure you have an adjacency on both links, and you architect l3
    properly. Just my 2 cents....
    Trendkill, Nov 25, 2008
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  3. John

    John Guest

    Not sure what you were trying to say "If you absolutely must have the
    same L3 networks available in both locations" please elaborate
    Thank you very much
    John, Nov 25, 2008
  4. John

    Trendkill Guest

    Do you need the same subnet available in both locations (i.e. or something similar)? If so, then you will need to
    architect a solution that puts the same subnet (i.e. vlan) in both
    locations. This limits your options to trunking or something
    similar. If you don't need the same l3 network in both location, then
    create new subnets in the 2nd facility, summarize them together, and
    advertise them back to the main office. That way each office has two
    paths to the other's l3 networks, and can failover as necessary in the
    event of an issue. Unless you absolutely have a requirement for two
    boxes (one at each location) to be in the same L3 subnet (private
    vlans for oracle or load balancing servers can drive this type of
    requirement), I would avoid a l2 based solution.
    Trendkill, Nov 25, 2008
  5. John

    John Guest

    Thank you very much
    John, Nov 25, 2008
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