split horizon in the OSPF

[Nehadeepu]

How OSPF will prevent from the Loop and What is Split Horizon in the OSPF?

[Deepak Kumar · Accepted solution]

Hi,

Split horizon means: we received some route via an interface, accepted it (put into RIB) and, will not announcement back to use that same interface. OSPF doesn't have Split Horizon. OSPF floods LSA not as a result of RIB update, but as a requirement for consistent LSDB. So, LSA would be forwarded further even if you filtered the prefix out of RIB.

What is Split Horizon in the OSPF?

As mentioned OSPF doesn't have Split Horizon. OSPF uses the SPF calculation to determine the shortest loop-free path to a destination for all destinations within an area.  Area 0 makes the OSPF Hierarchy loop-resistant when combining multiple areas because of two important rules in OSPF:

• Having a backbone area and requiring all other areas connect to it creates a point to point topology which in itself is resistant to loops.
• Having ABRs reject any Type-3 LSA that is received over a nonbackbone area.

Regards,

Deepak Kumar