Loop Prevention Mechanism

Loop Prevention Mechanism

A routing loop is a serious network problem that occurs when a data packet is routed through the same routers repeatedly. The network continues to route data packets within the network in an endless circle. A routing loop can have a catastrophic impact on a network and, sometimes, can completely disable the network.

• Routing loop-data packets are continually routed through the same router, over and over, which results in the following issues:

  1. Bandwidth is consumed

  2. Processing power is lost

• Loop prevention mechanisms are available:

  1. Down (DN) Bit in OSPF

  2. Site of Origin (SoO) Community in BGP

  3. Propagate AS in BGP

  4. External Protocol field in EIGRP

If you have a routing loop in your network, a major portion of the limited bandwidth that is available for normal user traffic of the affected routers is consumed by looping IP datagram packets and the major portion of the processing power is used to process the looping IP datagram packets.

Route Redistribution—Default Behavior

To avoid propagating excessive routing information from the edge to the access portion of the network, the routes that WAN Edge routers receive through OMP are not automatically redistributed into the other routing protocols running on the routers. If you want to redistribute the routes received through OMP, you must enable this redistribution locally on each WAN Edge router.

To avoid routing loops and less than optimal routing, redistribution of the following types of routes requires explicit configuration:

• BGP

• OSPF external routes

• EIGRP

OSPF Route Redistribution