OSPF best practice for COST

PeraHoman
PeraHoman used Ask the Experts™
on
If hardware is all the same, what's best practice for OSPF cost?


Left:
Egress and ingress are opposite of one another.  (Egress/Ingress are not on the same connection)  I like this setup, but i'm not sure if its best practice compared to the far right picture.  I prefer this idea because inflow/outflow aren't shared on a link, but is this enough justification to be BP?

Middle:
Each core will be responsible for their "side". (Left core/distro vs right core/distro)  Not sure if this is correct...i'm just guessing

Right:
Primary/Secondary setup.  (Left core takes care of everything, Right Core is backup)
OSPF-FLOW.png
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Distinguished Expert 2018
Commented:
None of those.

OSPF is capable to do equal cost path selection (to use both paths to reach some destination). Additionally on pictures are multi layer switches. Forwarding plane that is configured with IP CEF will by default (on newer devices use universal algorithm - source IP destination IP and hash) be able to perform load balancing (around 50:50 per link). Additionally each cable has transmitting (Tx) and receiving pair (Rx) (in the case of full duplex), so there is no need to use one link for sending traffic and other for receiving traffic (except if your interfaces work as half duplex).
So, typically, the best cost configuration is that all interfaces have the same cost (of course, if interfaces have the same speed) and to use all link simultaneously for sending and receiving traffic and let OSPF will choose the best paths.
The only problem is that depending on place where traffic is load balanced can have unpredictable results under some circumstances. But, if you have OSPF configured in network core you will want, for sure, equal cost load balancing to take place.

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