Re: EIGRP DUAL Variance

Any of ya'll seen this behaviour, just bumping!

--
BR
Tony
Sent from my iPad
> On 6 Oct 2013, at 19:53, 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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