Multiple ISPs and Multiple IP Ranges from Each ISP

Discussion in 'Cisco' started by Chennak, Jun 3, 2005.

  1. Chennak

    Chennak Guest

    I have Multiple ISP Internet links and Multiple Valid IP ranges from
    Each ISPs..

    I have configured to use both ISP lines using Route Maps.

    For Example let my First Range be from ISP-A
    let my Second Range be from ISP-B. Traffic from First
    range will use ISP-A's Internet Link and others will use ISP-B's link.

    Now, I want to Enable Redundancy between these two links...If one fails
    let it use the other.

    My Question here is, Will My ISPs will Route the packet from the other
    Say Suppose, My Internet link to ISP-A is down.
    Now, all my Internet traffic should go thru' ISP-B..that's, Will the
    traffic from will reach Public world thru' ISP-B..?

    If it is possible how do i do that??

    Can somebody help me on this??

    Thanks in advance..
    Chennak, Jun 3, 2005
    1. Advertisements

  2. Chennak

    Per Heldal Guest

    No! That would break the internet's basic principle of hierarchical
    distribution of resources (addresses).

    You can achieve redundancy for *outbound* traffic using some form of
    NAT-configuration where the NAT-device is able to detect that one of the
    connections is down. Redundancy for inbound connections is not possible.
    To achieve what you really need requires that you obtain your own
    (provider independent - PI) addresspace. Your provider(s) should be able
    to tell you if it is possible, and if so what the policies and
    requirements for such configurations are in your region.
    Per Heldal, Jun 3, 2005
    1. Advertisements

  3. That's not entirely true. There are at least two ways
    to achieve redundancy without own IP address space:

    1. Device supported

    For example Cisco PIX allows you to define multiple
    peers for one VPN connection. If one peer fails, PIX
    will try the next IP address.

    2. DNS method

    Multi-homing devices (like Nortel Alteon Link Optimizer)
    act as DNS servers and to DNS queries they will return
    an IP address that is preferred at the time (this can
    be either fault tolerant based or load balancing based).
    Jyri Korhonen, Jun 3, 2005
  4. :To achieve what you really need requires that you obtain your own
    :(provider independent - PI) addresspace. Your provider(s) should be able
    :to tell you if it is possible, and if so what the policies and
    :requirements for such configurations are in your region.

    It would not -necessarily- have to be Provider Independant -- but
    you would need the agreement of the providers involved to put the
    address space into an AS and advertise routes to it. The backbone
    routers aren't going to be very happy about that if the address
    spaces are embedded in large blocks they would otherwise
    supernet, but their grumpiness would be reduced if the two ISPs
    involved were "close by" (in routing space) so that -most- of the
    net could continue to use a single route.

    For example, the largest carrier by far in these parts is "MTS",
    so ARIN strongly encourages people to get address space from MTS --
    including regional ISPs. Any regional ISP worth its salt isn't
    going to have a "single point of failure" just because it's address
    space was SWIP'd from a different ISP. But at some point there
    are effectively network boundaries for MTS address space, and
    as long as those several boundaries know to do the route splitting,
    the rest of the world only needs to know how to route to the MTS
    boundaries. If one then multihomed between the regional ISP and MTS
    directly, then it could all work even without "Provider Independant"
    Walter Roberson, Jun 3, 2005
  5. Chennak

    Per Heldal Guest

    Sounds like a bad idea to me. Any decent provider that operate according
    to RIR-recommendations would filter "orphan" blocks. As you say, it is
    possible for two or more providers to cooperate in such a way that it is
    invisible to the rest of the world. However, such a configuration is a
    nightmare to maintain and I think you'll have a problem to find anybody
    willing to operate such a thing.
    Despite possible workaround my recommendation remains: Use PI-space if
    you're big enough to qualify. If not, build redundancy with only *one*
    upstream. Any ISP who wants to be taken seriously as a supplier of
    business-critical communications already have serious redundancy built
    into their own network and the ability to offer redundant connections to
    customers (connect to more than one POP etc). I.e. choose a decent
    supplient instead of trying to build your own solutions for redundancy.

    Per Heldal, Jun 5, 2005
  6. Chennak

    Per Heldal Guest

    Only if you place requirements on applications. I was thinking
    industrial-strength redundancy that would also would allow e.g.
    TCP-sessions to stay active. There are workarounds if you lower the
    requirements somewhat.
    This only works if you control the application/equipment at both ends
    of the packet-stream. The original question didn't indicate that.
    DNS-based redundancy works ... to some extent. However, it requires
    off-site equipment (outside the address-block to be protected) or that you
    can buy such services elsewhere. Also, don't depend on it for "quick
    failover". No matter how much you lower your TTL there will always be
    enough caching servers and cacheing applications out there to give you
    plenty of problems. Now, you can always say it's their problem if they're
    not standards-compliant, but that's a whole other discussion.

    Per Heldal, Jun 5, 2005
  7. Yes, you are right saying that one can't achieve high
    level redundancy using "cheap tricks". However people
    posting here are usually after the cheap tricks.
    Somebody who really wants and needs redundancy doesn't
    post a question here - he will hire a consultant.
    Again yes. I can see that you have been there, done that
    and probably got even the T-shirt.
    Jyri Korhonen, Jun 5, 2005
  8. :Yes, you are right saying that one can't achieve high
    :level redundancy using "cheap tricks". However people
    :posting here are usually after the cheap tricks.
    :Somebody who really wants and needs redundancy doesn't
    :post a question here - he will hire a consultant.

    Unfortunately, -particularily- when it comes to redundancy, we are
    seeing a non-trivial number of people coming here who "really want and
    need redundancy", wanting to know which -one- statement they need to
    add (or which one radio box to click in the GUI) in order to achieve
    bi-directional packet-level load balancing -and- sub-10-second
    failover between different residentially-oriented broadband providers.

    Some of those people realize quickly that it isn't quite that simple
    and that they'd best get someone in to help; but some of the people are
    quite persistant in their belief that not only should we be able to
    "just give them a few commands", but also that we should do so promptly
    and eagerly -- "I posted this a long time ago {55 minutes}, why hasn't
    someone answered yet!?!"
    Walter Roberson, Jun 5, 2005
  9. Chennak

    Hansang Bae Guest

    What!?! Am I the only one clued into the

    conf t
    ip bidir load-balance all-link


    conf t
    router ospf 1
    area 0 subsecond-convergence


    OK...admit it! How many of you *just* tried this! :)

    The danger of hiring consultants is that there are too many stupid ones!



    "Somehow I imagined this experience would be more rewarding" Calvin
    **************************ROT13 MY ADDRESS*************************
    Due to the volume of email that I receive, I may not not be able to
    reply to emails sent to my account. Please post a followup instead.
    Hansang Bae, Jun 8, 2005
  10. Right, now all we need is the same for PIX OS 7.0.
    And please don't mix OSPF into it because that
    will only confuse most inquirers.
    Jyri Korhonen, Jun 8, 2005
  11. I'm sensing a little bitterness. I can understand that because
    that's how these things work. In Finland we have a proverb

    "Yksi hullu kysyy enemmän kuin kymmenen viisasta ehtii vastata."

    which roughly translated means

    "A madman can make so much questions that ten wise men can't
    manage to give the answers."

    In your case that has often been only one wise man when
    you have single-handedly kept up PIX support here. Well,
    it may be cold comfort but I can say that if I have a PIX
    problem then my first thought is not "I'll call our provider"
    and not "I'll contact TAC". It is "I'll write to
    and ask Walter".
    Jyri Korhonen, Jun 8, 2005
    1. Advertisements

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.