From: Clay K Auch \(clauch\) (clauch@cisco.com)
Date: Mon Sep 24 2007 - 12:34:31 ART
Hello members,
The following information has helped me tremendously when dealing with Tunnels. The information is regarding recursive routing loops which pertains directly to which interface you may or may not use: (enjoy) ... I have also provided the link below the text:
========================== recursive routing loop (tunnel)========================
When tunneling IP over IP, you must be careful to avoid inadvertently configuring a recursive routing loop. A routing loop occurs when the passenger protocol and the transport protocol are identical. The routing loop occurs because the best path to the tunnel destination is via the tunnel interface. A routing loop can occur when tunneling IP over IP, as follows:
--> 1) The packet is placed in the output queue of the tunnel interface.
--> 2) The tunnel interface includes a GRE header and enqueues the packet to the transport protocol (IP) for the destination address of the tunnel interface.
--> 3) IP looks up the route to the tunnel destination address and learns that the path is the tunnel interface.
--> 4) Once again, the packet is placed in the output queue of the tunnel interface, as described in Step 1, hence, the routing loop.
When a router detects a recursive routing loop, it shuts down the tunnel interface for 1 to 2 minutes and issues a warning message before it goes into the recursive loop. Another indication that a recursive route loop has been detected is if the tunnel interface is up and the line protocol is down.
To avoid recursive loops, keep passenger and transport routing information in separate locations by implementing the following procedures:
*Use separate routing protocol identifiers (for example, igrp 1 and igrp 2).
*Use different routing protocols.
*Assign the tunnel interface a very low bandwidth so that routing protocols, such as IGRP, will recognize a very high metric for the tunnel interface and will, therefore, choose the correct next hop (that is, choose the best physical interface instead of the tunnel).
*Keep the two IP address ranges distinct; that is, use a major address for your tunnel network that is different from your actual IP network. Keeping the address ranges distinct also aids in debugging because it is easy to identify an address as the tunnel network instead of the physical network and vice versa.
========================
http://www.cisco.com/univercd/cc/td/doc/cisintwk/idg4/nd2002.htm
========================
HTHs
Clay
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of shiran guez
Sent: Monday, September 24, 2007 10:53 AM
To: alexandros.sichlimiris@bt.com
Cc: ccielab@groupstudy.com
Subject: Re: Tunnel Config
I think this discussion is going no where, I am sorry if any one got offended, my opinion still remain against 2 cent advice.
THAT IS MY OPINION for 2 CENT :-)
On 9/24/07, alexandros.sichlimiris@bt.com <alexandros.sichlimiris@bt.com>
wrote:
>
> Hi Shiran, when someone is asking for an opinion when choosing between
> two options and not for a specific explanation of a technology, then
> you would see a "2 cents" reply. This doesn't mean that whoever
> replied does not know 100% the technology, it simply means that this
> is his opinion on how to best implement the technology in question.
> In short, a "2 cents" answer does not imply a less than perfect
> knowledge of the technology.
>
> Cheers,
> Alex
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> Of shiran guez
> Sent: 24 September 2007 14:08
> To: Alexander Belov
> Cc: Tandou Mohamed; ccielab@groupstudy.com
> Subject: Re: Tunnel Config
>
> guys although every opinion count here I think that to give this "2
> cent advice" is the worse we can do, if we want to consider our self
> Experts then we need to act like it and understand that there are very
> few 2 cent advice and mostly are focused on tricks like making the
> status prompt on the IOS disappear.
>
> but as far as technology there are no "2 cent advice" it is either you
> understand or you do not, and if you do not understand then your "2
> cent advice" will work may be 90% if you lucky but in case you get a
> question that need your full understand it will not work and you will
> not know why.
>
>
> I hope that more will agree with me on that view
>
> On 9/24/07, Alexander Belov <abelov@technoserv.ru> wrote:
> >
> > Hi mate!
> >
> > I'd say - Loopback IPs for tunnel source/dest and /30 network on
> tunnel
> > (ip
> > address 192.168.x.1/30 vs ip address 192.168.x.2/30)...
> >
> > My 2 cents
> >
> > -----Original Message-----
> > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> Of
> > Tandou Mohamed
> > Sent: Monday, September 24, 2007 4:12 PM
> > To: ccielab@groupstudy.com
> > Subject: Tunnel Config
> >
> > GS,
> > When configuring a tunnel interface, what is the best option to use
> for
> > tunnel source and tunnel destination if no direction is given? i
> always
> > use
> > the loopback interface for tunnel source and destination and also
> > for tunnel ip address using ip unnumbered. Some of the vendor
> > workbooks sometimes
> use
> > loopback or physical ip addresses. Can someone explain if i am doing
> > something wrong ?
> >
> > Thanks,
> >
> > TM
> >
> >
> > ---------------------------------
> > Moody friends. Drama queens. Your life? Nope! - their life, your
> story.
> > Play Sims Stories at Yahoo! Games.
> >
> >
> ______________________________________________________________________
> _
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> >
> >
> ______________________________________________________________________
> _
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> >
>
>
>
> --
> Shiran Guez
> MCSE CCNP NCE1
> http://cciep3.blogspot.com
>
> ______________________________________________________________________
> _ Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
>
-- Shiran Guez MCSE CCNP NCE1 http://cciep3.blogspot.com
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