Load sharing in OSPF

[abdul.qadir5001]

How OSPF perform load sharing. Does load sharing and load balancing are same things?

[Giuseppe Larosa]

Hello @abdul.qadir5001 ,

OSPF can perform Equal Cost Multi Path  ECMP

by default maximum-paths is 4 so by default up to 4 routes to same destination can be installed if they have the same total metric for the SPF algorythm.

Maximum-paths ca be increased to 8 or 16 this is platform dependent.

When ECMP is happening , load balancing is performed by CEF and it is flow based that is given a source IP address and a destination IP address one of the link is used for all packets in the same flow.

Load sharing is a different concept and it applies when for prefix A is used link1 for prefix B link 2 and so on. It is an approssimation of load balancing used in iBGP before the introduciton of iBGP multipath.

To be noted being OSPF the routes that are compared have to be of the same type intra area O route or inter O IA or O E1 or O E2.

Routes of different types even if they have the same metric are not compared there is a hierarchy:

O is preferred over O IA that is preferred over O E1 that is preferred over O E2

Hope to help

Giuseppe

[balaji.bandi]

Adding to @Giuseppe Larosa  post what he said correctly in OSPF.

Does load sharing and load balancing are same things?

Load balancing is more of a dynamic technique of distributing the load across 2 or more links while Load Sharing works by statically splitting the traffic types and then distributing the load across multiple links.