Routing Loop in Redistribution

Centralized, distributed, or collaborative computing can be used as the foundation for a computer network’s communication. Numerous workstations or terminals are connected to a single central mainframe or another potent computer in centralized computing. One or more personal computers can be connected via distributed computing, which enables a variety of services like data sharing, hardware sharing, resource sharing, and network sharing. Combining centralized and distributed computing is what is known as collaborative computing.

Routing Loop:

The process of routing aids a packet in selecting the best route to take in order to get there as quickly as feasible. When one routing protocol broadcasts a route that another routing protocol has redistributed and learned, the situation is known as a routing loop. A routing loop is a problem that arises when packets are forwarded by routers in such a way that they constantly arrive at the same router in the network due to the routing table’s anomalous behavior when the packets are frequently routed between two or more routers.

Redistribution:

Redistribution is the practice of using a routing system to promote routes that have already been discovered via different techniques, such as static routes, directly related routes, or another routing protocol. Even though it’s preferable to use a single routing protocol across the whole IP network, multi-protocol routing is frequently used due to a variety of factors, such as company mergers, several departments managed by different network managers, and multi-vendor setups.

Concept of Routing Loop in Redirection:

• The loss of the original data about a reachable network, including its original metric and topological presence, is what truly causes routing loops in redistribution. 
• Redistributing involves pulling information about a certain network’s existence from one protocol and injecting it into another, however doing so results in the loss of a number of network-specific data. As a result, a routing protocol could begin to believe false information and eventually create a loop.
• Different routing protocols are frequently used as part of network designs. Redistribution is required in an environment with several protocol types. 
• Redistribution may be impacted by variations in the attributes of the routing protocol. These variations must be taken into account for redistribution to succeed.

Example:

Consider three routers, X, Y, and Z. Assume that X/Y and X/Z links are used for the RIP. Additionally, Y and Z operate OSPF on their shared link (you may assume that there are other routers attached to Y and Z which are not displayed at the exhibit but which speak only OSPF). Now think about the subsequent procedure, A network T is discovered by X using RIP with a metric of 7, and X then sends this network to Y and Z using a metric of 8. X will be the next hop for both Y and Z in their journey to network T. Y is set up to switch from RIP to OSPF redistribution. As a result, Y switches the network T from RIP to OSPF and transmits it to Z with a metric of, let’s say 3000.
RIP and OSPF are now Z’s two sources of knowledge about the network T. The redistributed OSPF route, pointing back towards Y, substitutes the RIP-learned network T in Z’s routing table because OSPF employs an administrative distance of 120 and is hence more reliable than RIP.
Z redistributes the network T from OSPF back to RIP with a metric of, say, 3, as it is configured for redistribution from OSPF to RIP. Now that X has learned about the network T from Z, it updates its routing table and begins pointing to Z as the next hop due to the reduced metric.
As of right now, X points to Z, Z to Y, and Y then points back to X, creating a perpetual routing loop.
A route from a routing protocol with a higher AD was really extracted, put into a protocol with a lower AD, and then reinjected into the original protocol with the higher AD, which is what created the issue. A RIP-learned route was used in this case to enter OSPF on Y and then re-inject it into RIP on Z.

The RIP is less reliable than OSPF (since its AD=130 is less than OSPF AD=120), therefore the Z won’t go back to using the RIP-learned route via X directly.
Never re-advertise a network back into the routing protocol it was initially created with is the solution. To do this, route marking, filtering, or adjusting administrative distances may be used.

Advantages:

• Route redistribution enables the advertisement of routes from one routing protocol to another. 
• Route redistribution enables the advertisement of routes from one routing protocol in another routing protocol.
• One of the symptoms of the redistribution loop will be a routing table will get updated constantly.
• Increases security because only the administrator can permit routing to certain networks.
• Single point of failure can be reduced by redistribution.

Disadvantages:

• Redistribution can be affected by variations in the metrics, administrative distance, and classful, and classless capabilities of the routing protocol.
• For redistribution to be successful, inequalities must be taken into account. There are no particular specifications.
• It results in Route Poisoning and the Problem of Counts to Infinity.
• Bandwidth wastage
• Routing loops not only suck up a lot of valuable network bandwidth but also trick the router into thinking a network that isn’t there is.

Application:

• When we redistribute traffic from a protocol with a higher AD to a protocol with a lower AD, routing loops frequently result. This indicates that RIP is typically implicated.
• Used when two businesses unite and each uses a distinct routing protocol.
• Utilized in conjunction with MP-BGP or VRFs.
• Allow communication between various networks owned by the same company.
• Can be used for dynamic routing protocols.