The use of a routing protocol to advertise routes that are learned by some other means, such as by another routing protocol, static routes, or directly connected routes, is called redistribution. While running a single routing protocol throughout your entire IP internetwork is desirable, multi-protocol routing is common for a number of reasons, such as company mergers, multiple departments managed by multiple network administrators, and multi-vendor environments. Running different routing protocols is often part of a network design. In any case, having a multiple protocol environment makes redistribution a necessity.
Redistribution can be done through:
- One-point redistribution
- Only one router is redistributing one-way or two-way (both ways).
- There could still be other boundary routers but they are not configured to redistribute.
- Multiple routers are used to redistribute either one-way or two way (both ways).
- More prone to routing loop problems.
One-point redistribution can be configured in either:
- One-point One-way
- Redistributes networks from one routing protocol into the other routing protocol.
- Typically uses a default or static route so that devices in that other part of the network can reach the first part of the network.
Redistributes routes between the two routing processes, in both directions.
One-Point One-Way Redistribution Issue
Although one-point one-way or two-way redistribution is usually safe from routing loops, issues can still occur if multiple boundary routers exist and only one router is performing one-point one-way redistribution.
In this example, R2 is redistributing an external EIGRP route into the OSPF domain.
Multipoint redistribution has two (or more) separate routers running both routing protocols. Redistribution can be configured as:
- Multipoint one-way redistribution
- Multipoint two-way redistribution
Although multipoint two-way redistribution is especially problematic, either method is likely to introduce potential routing feedback loops.
Multipoint one-way redistribution only works well if:
- The receiving routing protocol is either EIGRP, BGP and OSPF because they support different administrative distances for internal and external routes.
- The administrative distance of protocol B’s external routes is higher than the administrative distance of protocol A’s routes, so that R2 and R3 will use the appropriate routes to destinations in the protocol A side of the network.
Answer the Following Questions
- What is the use of the redistribution
- Which method are you using between OSPF & RIP
- Can we use both at a time One-Point One-Way Redistribution & One-Point Two-Way Redistribution
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