Re: EIGRP best path selection with multiple successors

A complete wild guess but does the H age timer matter here i.e peer that's been up the longest then prefer the route from him, a la OSPF LSA type1

I guess bouncing the peers would disprove this theory..

--
BR
Tony
Sent from my iPad
> On 11 Dec 2013, at 23:07, Joe Astorino <joeastorino1982_at_gmail.com> wrote:
> 
> Just to expand a bit - Let's say you have a simplified version of the DMVPN
> network in this documentation.  Say you have a single hub and 3 spokes, S1,
> S2 and S3 and your network is a DMVPN phase 2 design running EIGRP.  We
> know that in Phase 2 design on the hub, we would both disable split-horizon
> and we would use "no next-hop-self eigrp" on the hub. This allows the DMVPN
> hub to learn spoke routes on the tunnel interface, then turn around and
> advertise them back out the same multipoint tunnel to other spokes with the
> original next-hop intact.  Thus, we can allow dynamic spoke to spoke
> tunnels.
> 
> Now, say S1 and S2 are both connected to the same LAN segment and both
> advertise this subnet with the same composite metric to the hub.  The hub
> will have 2 successors to this network, but as the article states, by
> default will only advertise one of them to S3.  The question is which one
> and why? The article only mentions that EIGRP will select one but does not
> go into detail as to how this happens.  At S3, is the next-hop of the LAN
> subnet going to be S1 or S2 and why?
> 
> 
> On Wed, Dec 11, 2013 at 5:24 PM, Joe Astorino <joeastorino1982_at_gmail.com>wrote:
> 
>> So, the new EIGRP "add-path" feature is intriguing to me as documented
>> here
>> http://www.cisco.com/en/US/docs/ios-xml/ios/iproute_eigrp/configuration/xe-3s/ire-add-path.html
>> 
>> As we know, EIGRP can indeed have multiple equal cost paths.  In that
>> case, we will see more than one successor in the EIGRP topology table.
>> However, only one is actually sent to EIGRP neighbors by default, as the
>> article points out.
>> 
>> In certain DMVPN situations, this does not allow spoke to spoke load
>> balancing, hence the point of the add-path feature as explained.
>> 
>> All that is well and good, but I couldn't help asking myself as I was
>> reading "wait a minute, by default without all this, which successor would
>> it send?"
>> 
>> I have spent some time googling around and such and have labbed some
>> things up, but have not got a definitive answer.  Anybody know?
>> 
>> In my lab test I had frame-relay hub and spoke network setup.  The spokes
>> are both connected to the same ethernet segment and I had them redistribute
>> that ethernet segment into EIGRP with the same metric, but using different
>> route tags.  My initial experiments seemed to indicate that the successor
>> sourced from the neighbor with the lowest IP address were sent upstream to
>> other EIGRP neighbors.
>> 
>> --
>> 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
> 
> 
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