Re: a routing question from Jafar T on 2009-04-22 (Ccielab archives 04/2009)

From: Jafar T <jafar_at_paris.com>
Date: Wed, 22 Apr 2009 01:36:54 -0500

Thanks Pavel

  ----- Original Message -----
  From: "Pavel Bykov"
  To: "Joe Astorino"
  Cc: "Jafar T" , ccielab_at_groupstudy.com, "Bryan Bartik"
  Subject: Re: a routing question
  Date: Wed, 22 Apr 2009 08:05:03 +0200

  I believe this is the best solution as well. Just don't make it ping
  google, or some other subnet further inside ISP, because that will
  result in flapping:
  1. DSL failed
  2. SLA triggers failover
  3. Router B is primary
  4. SLA detect connectivity
  5. Router A is primary... connectivity is lost. GO TO 2

  So you need to ping IP address on the other side of DSL interface,
  because that subnet will never be reachable through Router B if it is
  down.

On Wed, Apr 22, 2009 at 5:26 AM, Joe Astorino <joe_astorino_at_comcast.net>
wrote:

    Well, once your DSL comes back up, your SLA will come back up,
    which will trigger your static default route to be entered back
    into your routing table....and that will have a lower AD than the
    one learned from router B so you will be all set. It's completely
    dynamic.

"He not busy being born is busy dying" -- Dylan

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    ----- Original Message -----
    From: "Jafar T" <jafar_at_paris.com>
    To: "Joe Astorino" <joe_astorino_at_comcast.net>
    Cc: ccielab_at_groupstudy.com, "Bryan Bartik" <bbartik_at_ipexpert.com>,
    "Jafar T" <jafar_at_paris.com>
    Sent: Tuesday, April 21, 2009 11:23:40 PM GMT -05:00 US/Canada
    Eastern
    Subject: Re: a routing question

    where to find a good sample for this config, and would this work,
    even the ip address is now rechable thru router B ?
    how to fall back from it once dsl link is up

thx

    ----- Original Message -----
    From: "Joe Astorino"
    To: "Joe Astorino"
    Cc: ccielab_at_groupstudy.com, "Bryan Bartik" , "Jafar T"
    Subject: Re: a routing question
    Date: Wed, 22 Apr 2009 03:06:30 +0000 (UTC)

    *edit* I meant the default route coming from router B would have
    a
    HIGHER AD , and thus be less preferable.

"He not busy being born is busy dying" -- Dylan

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    ----- Original Message -----
    From: "Joe Astorino"
    To: "Jafar T"
    Cc: ccielab_at_groupstudy.com, "Bryan Bartik"
    Sent: Tuesday, April 21, 2009 11:02:14 PM GMT -05:00 US/Canada
    Eastern
    Subject: Re: a routing question

    I did something similar to this before. Building on what Bryan
    said, setup ip sla to do something like ping the default gateway
    your DSL ISP gives you. At the same time, have router B advertise
    a
    default route to router A. So, router A should have a static
    default route tied to the SLA pointing to your DSL, and a default
    route with a lower AD advertised from router B. If the SLA ping
    fails, your static route goes away and the one being advertised
    from router B kicks in.

"He not busy being born is busy dying" -- Dylan

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    ----- Original Message -----
    From: "Jafar T"
    To: "Bryan Bartik"
    Cc: ccielab_at_groupstudy.com
    Sent: Tuesday, April 21, 2009 10:49:44 PM GMT -05:00 US/Canada
    Eastern
    Subject: Re: a routing question

    thanks for the idea,
    but will not work, i always want A to use that static to
    firewall, i just
    want A to fail over if the dsl on the far far side of that
    fireall drops,
    in other words, if the dsl drops, A switch to B
    how can i do this tweak, without changing the FW config ?

thanks

    ----- Original Message -----
    From: "Bryan Bartik"
    To: "Jafar T"
    Cc: ccielab_at_groupstudy.com
    Subject: Re: a routing question
    Date: Tue, 21 Apr 2009 20:29:42 -0600

    It sounds like you need Router A to recognize when it should no
    longer use
    it's static default route, remove it, and then use the route
    towards
    B. You
    can create an SLA Tracker and tie it to the route. One thing you
    would watch
    out for is that whatever you track through the firewall is not
    reachable
    through Router B, otherwise the tracker would pass and the route
    would come
    up again. Although, maybe you could tweak the tracker to
    differentiate...Any
    other ideas?

    Bryan Bartik
    CCIE #23707, CCNP
    Sr. Support Engineer - IPexpert, Inc.
    URL: http://www.IPexpert.com

On Tue, Apr 21, 2009 at 8:02 PM, Jafar T wrote:

> hi team, i have a scenario,
    isp.......routerB......mpls/BGP.......router
    A.....firewall.....dsl...isp
>
> routeb, needs to act as a failover for A internet traffic
    router
> A, only has a static route to Firewall interface, routerA, will
> never detect the the dsl link down, since it is on
    another
> subnet so no matter what router B advertise, floting
> static..default originate....etc it willl be no good for A, it
> can see that in the table, looks
    good, but
> will never be activated as a another default route, since A
    always
    will
> see the static route to firewall, and it looks fine as far as
    the
    router
> a can tell, how can you change that, without enable a routing
> protocol on the firewall, in another words,
    without
> doing any changes on the firewall ? cheers JT -- It's News.
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