Load-Sharing/Load-Balance on Cisco Tunnel Interfaces & Maximum-path

[byme88]

Hi Everyone,

I have a few questions regarding EIGRP, it related to the Load-Sharing/Load-Balance on Cisco Tunnel Interfaces with Maximum-path not configured.

There are 2 Tunnel interfaces configured with Delay for primary selection in EIGRP process; I have a couple of questions listed below:

1. If I don't configure the maximum-path, will the traffic be Load-Sharing/Load-Balance on both tunnels? Or the delays of EIGRP will still be playing the decision to choose the primary path here?

2. Should I configure the maximum-path to 1 to disable the Load-Sharing/Load-Balance on the tunnel in this case and still achieve the redundancy configured by delay in EIGRP?

Thank you all in advance.

Byme88

[MHM Cisco World]

GRE tunnel with config EIGRP delay make EIGRP select one path there is no load balance if the delay is different.
this link give you exactly what you want 
 https://journey2theccie.wordpress.com/2020/04/24/dmvpn-dual-hub-dual-cloud/

[MHM Cisco World]

in link I share 
increase the delay in Tunnel YOU DONT WANT TO SELECT AS PRIMARY. 

[Joseph W. Doherty]

#1 By default, EIGRP does ECMP, also by default, I believe (?), usually allowing up to 4 paths (as I recall it used to).  ECMP (equal cost multiple path), would, as name implies, requires all the paths to have the same cost.  Having tunnels, with different delay values likely will cause different costs, and if so, only the best path would be chosen.

#2 Hmm, I presume you could do that, but than, which tunnel would tunnel would be chosen?  If that doesn't matter, the limiting paths to 1 should do the trick, but if you adjust metrics, you get to chose primary vs. secondary.  Also with explicit primary vs. secondary, if primary fails, secondary takes over, but when primary comes back on-line, it should pre-empt secondary.  So, also with paths set to 1, if one path is chosen as best path, and it fails, other path should take over, but when first path restored, would expect the alternative path to continued to be used.  I.e. really depends on what behavior you want.

BTW, EIGRP also supports proportional multi-path usage too, but that's not active, by default.

[byme88]

Hi Joseph,

Thanks for the input, regarding #2 question

"#2 Hmm, I presume you could do that, but than, which tunnel would tunnel would be chosen? "

This is importance because we chose the primary tunnel to be the primary path with lower delay.

Thanks,

byme88

[Joseph W. Doherty · Accepted solution]

Ok, then just insure your primary path has a better metric than your secondary path.

Doing that, the maximum-path parameter won't matter, so I would suggest you leave it at its default setting.

[MHM Cisco World]

This eigrp not ospf, and because eigrp support unequal path then I must be so careful because,

One article in ccie suggests to be aware in link or tunnel between two hub in config delay of spoke tunnel, 

To be honest I dont understand what he talking about and that why i dont full answer you.

But some think and focus i get what he talk about.

Why max must set 1 ?

If compare  the tunnel to hub 1

and

tunnel to hub2 + hub1 to hub2 path 

And if both match unequal criteria then there chance that spoke can select two path if max set not 1.

So it better to be 1 

Also ccie articles suggest that path spoke to hub1 compare to hub1 to hub2 must be higher.

This prevents hub2 to use spoke to reach hub1.

Hope this help you and all read this post later.

MHM