Re: EIGRP DUAL Variance

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
>
>
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-- 
Regards,
Joe Astorino
CCIE #24347
http://astorinonetworks.com
"He not busy being born is busy dying" - Dylan
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