GRE/IPSEC Tunnel and loopback interface

Discussion in 'Cisco' started by Mimmus, Apr 30, 2007.

  1. Mimmus

    Mimmus Guest

    I have two internal routers with a serial interface connected to a "public"
    network (indeed it is the Internet but ISP allows communication only between
    two routers).
    As a backup link, I have to configure a GRE/IPSEC tunnel between routers,
    also carrying OSPF traffic for dynamic routing between sites.
    Provider gave me a /30 for point-to-point link and a /29, for each site..
    In all documents, I'm reading that I need to assign an IP from /29 to a
    loopback interface.
    Problem is that I'm not using loopback interfaces on my routers (I know... I
    know... they are useful...) and, in any case, I don't like having a public
    IP on my loopback.
    Is there some other way to proceed?

    Mimmus, Apr 30, 2007
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  2. Mimmus

    Bod43 Guest

    You can use ANY ingerface on the router as a tunnel

    The reason that loopbacks are preferred in general is that
    with some network designs it is possible for the tunnel
    source/dest interface to go down and even though there
    is another path the tunnel will do down too. The loopbacks are
    always up.

    I do not have a perfect picture of you network I don't think,
    but if each router has only one outside interface
    and no other path then there will be no disadvantage in
    using the external interface to terminate the tunnel.

    Beware recursive routing.
    I ALWAYS put in static routing to the tunnel endpoints.
    Bod43, Apr 30, 2007
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  3. Mimmus

    Mimmus Guest

    Exactly what I done!
    Tunnel is absolutely a Point-to-Point one and using the loopback interface
    caused some problems (see below...)
    Ok, I experimented this :-(
    I don't know exactly why but, using the loopback interface, I had some loop,
    peraphs due to another indirect link between tunnel endopoints advertised by
    OSPF. I was not able to filter it.

    Thanks again
    Mimmus, Apr 30, 2007
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