OSPF via secondary IP?

Discussion in 'Cisco' started by gkg, Nov 14, 2003.

  1. gkg

    gkg Guest

    I'm trying to set up an OSPF link through a non-OSPF-capable DSL link,
    using bridge mode. While running the OSPF update through on the primary
    IP works fine (i.e., OSPF neighbor is found right away, routing updates
    are fine), I would like to avoid having to transmit all the broadcast
    traffic of the POP site through the DSL link - therefore, I planned on
    setting up a /29 as transfer net for the OSPF connection. After setting
    the secondary IP of the /29 on the POP router, and adjusting the primary
    IP of the CP-router accordingly, I do not get any OSPF announcements. Is
    there a trick to force the Cisco to announce the stuff through the
    secondary IP, too? I have done the "network <NETIP> <MASK> area"
    ... Also, I can not switch between primary and secondary IP for the
    POP router, as then the OSPF wouldn't work there anymore :(

    Help appreciated,

    gkg, Nov 14, 2003
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  2. OSPF will only set up adjacencies using the primary address. But you can
    go ahead and filter all broadcasts without blocking OSPF. OSPF uses
    multicasts, not broadcasts, for LAN communications. Another alternative,
    but it requires you to reconfigure both ends, may be to configure OSPF to
    use the LAN as a point-to-point link. But that would require careful
    testing, and could present other challenges, particularly if there are
    any other routers on the LAN.

    The "standard" approach to this class of routing problems is to use a
    GRE tunnel, but I'm assuming you've already rejected that due to the
    impact on MTU size.

    Good luck and have fun!
    Vincent C Jones, Nov 14, 2003
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  3. Hm ... so I guess I just have to move the CP-Router into the broadcast
    domains of the POPs ... guess I still have to figure out how to set up
    this configuration with the least amount of ethernet ports:

    In order to connect this customer, which is running through two seperate
    DSL links to two different POPs (which are connected through our
    backbone), and using non-OSPF-aware DSL Router/Bridges for the basic
    connection, I need to set up the dynamic routing for
    redundancy/availability. The basic setup is a triangle:

    customer -------------- POP1
    | |
    | |
    | |
    POP2 -----------------|

    Both POPs operate with OSPF routing, with multiple routers. As both POP1
    and POP2 use different /24 nets, the CP-router will not be able to use
    the some ether network for use of OSPF, therefore this would require two
    interfaces for OSPF announcements ... or is there another way? Then, I
    would probably use secondary IP address to connect the customer firewall ...
    There are, currently two more ciscos in one location ... so I guess that
    one is out of the question, too ..

    I'm still hoping for an update for the DSL routers/bridges to show up
    that include OSPF, but I need to make sure I have a solution if this
    does not happen ...

    Tnx, -gg
    Garry Glendown, Nov 14, 2003
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