Explaining Split Horizon-
Split horizon is used to prevent routing loops, suppose if an interface receives a routing update from a neighbor router, split horizon prevents this receiving interface to advertise it back to the neighbor router who sent them.
In simpler terms Split horizon mechanism transmits the packet to all the attached nodes, except which has send the update. Also you don't have to enable split horizon or anything, it is by default enabled on the interfaces of Cisco Routers. This feature is mostly used by dynamic routing protocols especially by RIP,IGRP and EIGRP etc.
To See if the split horizon is enabled on particular interface or not use command:-
R1#sh ip int s0/0/0
OUTPUT------------------------------------------------------------->
Internet address is 172.168.40.1/24
Broadcast address is 255.255.255.255
Address determined by setup command
MTU is 1500
Helper address is not set
Directed broadcast forwarding is disabled
Outgoing access list is not set
Inbound access list is not set
Proxy ARP is enabled
Security level is default
Split horizon is enabled
Even though split horizon plays such an important role by being helpful in avoiding stupid confusing loops, but still there are certain cases where it cause problems too. After hearing my this claim you must be thinking, how can this cause a problem? After all, it seems reasonable not to send misinformation back to the originating router. Well, you see split horizon creates lots of problem when we are dealing with point to multi-point links, such as Frame Relay, also when multiple remote routers are connected to a single interface. But there is a solution to this, that we can use logical interfaces called sub-interface concept that we will learn when I will take vlan topic.
READ ALSO:- WHAT IS STATIC ROUTING?
READ ALSO:- WHAT IS DYNAMIC ROUTING?
Guyz if you have any doubts on split horizon ask me down in the comment box I will answer it immediately.
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