Re: EIGRP DUAL Variance

Dear Tony,

I would suggest you to run a different version of IOS and try out... I
can only suspect a bug here.

The behavior you are experience is indeed strange.. It is surprising
to see the route installed in RIB while it is not shown in topology
table.

Regards

On 10/7/13, Joe Astorino <joeastorino1982_at_gmail.com> wrote:
> Hmmmm....also this Cisco white paper seems to agree with the book and with
> how I thought it worked. They have a simplified version of what you are
> testing with easier to read numbers.
>
> In the example, the path through D is not chosen because it's metric is not
> < variance * FD. However, it also goes on to make this point:
>
> "Also, the reported distance of neighbor D is 25, which is greater than the
> feasible distance (FD) of 20 through C. This means that, even if variance
> is set to 3, the E-D-A path is not selected for load balancing because
> Router D is not a feasible successor."
>
> This seems to certainly be making the case that to be considered for
> unequal cost load balancing via variance, a path must first pass the
> feasibility condition. Clearly, your lab results show otherwise though.
>
> http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a008009437d.shtml#var
>
>
>
>
> On Mon, Oct 7, 2013 at 3:34 AM, Joe Astorino
> <joeastorino1982_at_gmail.com>wrote:
>
>> This certainly seems strange to me. Granted, it is like 4AM or something
>> here, but if you had asked me I would have thought EIGRP would not
>> consider
>> the F1/0 path for anything, given it doesn't meet the feasibility
>> condition. I'd certainly be interested to hear if anybody else has an
>> answer.
>>
>>
>>
>>
>> On Sun, Oct 6, 2013 at 2:53 PM, Tony Singh <mothafungla_at_gmail.com> wrote:
>>
>>> CCNP ROUTE 642-902 Official Certification Guide
>>>
>>> "Routes that are neither successor nor feasible successor can never be
>>> added to the IP routing table, regardless of the variance setting"
>>>
>>> I did a little lab
>>>
>>> --- r2 ---
>>> r1 ----r3 ---- r5 loopback 5.5.5.5
>>> ----r4 ----
>>>
>>>
>>> no variance
>>>
>>> all-links
>>> P 5.5.5.5/32, 1 successors, FD is 158720, serno 55
>>> via 10.0.0.1 (158720/156160), FastEthernet0/0
>>> via 20.0.0.1 (161536/158976), FastEthernet1/1
>>> via 30.0.0.1 (1790976/156160), FastEthernet1/0
>>>
>>> topology
>>> P 5.5.5.5/32, 1 successors, FD is 158720
>>> via 10.0.0.1 (158720/156160), FastEthernet0/0
>>> via 30.0.0.1 (1790976/156160), FastEthernet1/0
>>>
>>> global-rib
>>> D 5.5.5.5 [90/158720] via 10.0.0.1, 00:00:44, FastEthernet0/0
>>>
>>>
>>> the reason we choose f1/0 path as FS over f1/1 is due to the AD<FD of
>>> successor holding true even if it has a worse FD - expected behaviour
>>> and
>>> end result no load-balancing as no equal cost paths (max 4 equal cost
>>> paths
>>> by default)
>>>
>>>
>>>
>>>
>>> if I apply a variance of x2
>>>
>>>
>>>
>>> all-links
>>> P 5.5.5.5/32, 2 successors, FD is 158720, serno 52
>>> via 10.0.0.1 (158720/156160), FastEthernet0/0
>>> via 20.0.0.1 (161536/158976), FastEthernet1/1
>>> via 30.0.0.1 (1790976/156160), FastEthernet1/0
>>>
>>> topology
>>> P 5.5.5.5/32, 2 successors, FD is 158720
>>> via 10.0.0.1 (158720/156160), FastEthernet0/0
>>> via 30.0.0.1 (1790976/156160), FastEthernet1/0
>>>
>>> global-rib
>>> D 5.5.5.5 [90/158720] via 10.0.0.1, 00:00:53, FastEthernet0/0
>>> [90/161536] via 20.0.0.1, 00:00:53, FastEthernet1/1
>>>
>>>
>>> ok so we're now permitting the f1/1 path being installed as a viable
>>> load-balancing destination, this shows me two things, first that dual
>>> will
>>> permit a non-successor or non-feasible successor into global rib as
>>> viable
>>> load-balancing paths and second dual compares the end-to-end FD for
>>> making
>>> a decision on which path it would prefer to load-balance looking at the
>>> all-links topology as f1/1 has a lower FD than f1/0
>>>
>>>
>>>
>>> this does make the above argument invalid - im wondering if EIGRP has
>>> since
>>> been enhanced for this DUAL behaviour? if so then I guess the whole
>>> point
>>> for the statement in the first place was to avoid a loop i.e if you're
>>> not
>>> a successor or feasible successor then you a loop, what has changed?
>>>
>>>
>>> --
>>> BR
>>>
>>> Tony
>>>
>>>
>>> Blogs and organic groups at http://www.ccie.net
>>>
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>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>
>>
>> --
>> Regards,
>>
>> Joe Astorino
>> CCIE #24347
>> http://astorinonetworks.com
>>
>> "He not busy being born is busy dying" - Dylan
>>
>
>
>
> --
> Regards,
>
> Joe Astorino
> CCIE #24347
> http://astorinonetworks.com
>
> "He not busy being born is busy dying" - Dylan
>
>
> Blogs and organic groups at http://www.ccie.net
>
> _______________________________________________________________________
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html

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Received on Mon Oct 07 2013 - 18:59:15 ART