From: Clay K Auch \(clauch\) (clauch@cisco.com)
Date: Tue Sep 25 2007 - 08:48:39 ART
Gary,
Thank you very much for that tid-bit of information. That is definitely the kind of morsel that could be thrown our way come test time.
Clay
-----Original Message-----
From: Gary Duncanson [mailto:gary.duncanson@googlemail.com]
Sent: Tuesday, September 25, 2007 4:08 AM
To: Clay K Auch (clauch)
Cc: shiran guez; alexandros.sichlimiris@bt.com; ccielab@groupstudy.com
Subject: Re: Tunnel Config
Hi Clay,
Here's another old link that adds further on the flapping issues with tunnels.
http://www.cisco.com/warp/public/105/gre_flap.html
(sic) Tunnel interface status depends on the IP reachability to the tunnel destination. When the router detects a recursive routing failure for the tunnel destination, it shuts the tunnel interface down for a few minutes so that the situation causing the problem can resolve itself as routing protocols converge. If the problem is caused by misconfiguration, the link may oscillate indefinitely.
----- Original Message -----
From: "Clay K Auch (clauch)" <clauch@cisco.com>
To: "shiran guez" <shiranp3@gmail.com>; <alexandros.sichlimiris@bt.com>
Cc: <ccielab@groupstudy.com>
Sent: Monday, September 24, 2007 4:34 PM
Subject: RE: Tunnel Config
> 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.
>> >
>> >
>> ______________________________________________________________________
>> _
>> > Subscription information may be found at:
>> > http://www.groupstudy.com/list/CCIELab.html
>> >
>> >
>> ______________________________________________________________________
>> _
>> > Subscription information may be found at:
>> > http://www.groupstudy.com/list/CCIELab.html
>> >
>>
>>
>>
>> --
>> 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
>
> _______________________________________________________________________
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
>
> _______________________________________________________________________
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
This archive was generated by hypermail 2.1.4 : Sat Oct 06 2007 - 12:01:15 ART