Router Redistribution: Connecting Networks with Different Routing Protocols

Router redistribution is a process used in enterprise networking where routing information from one routing protocol is shared or “redistributed” into another routing protocol. This is commonly used in complex network environments where different parts of the network use different routing protocols, and there needs to be a way for these different parts to communicate and share routing information.

For example, consider a network where one segment uses OSPF (Open Shortest Path First) as its routing protocol, and another segment uses EIGRP (Enhanced Interior Gateway Routing Protocol). Without redistribution, these two segments would not be able to share routing information, and devices in one segment would not know how to reach devices in the other segment.

To enable communication between these segments, router redistribution can be configured on a router that connects the two segments. This router would be configured to redistribute routes from OSPF into EIGRP and vice versa. This means that the router takes the routing information it learns from OSPF and shares it with EIGRP, and it takes the routing information it learns from EIGRP and shares it with OSPF.

Here’s a simplified example of how this configuration might look on a Cisco router:

router ospf 1
 redistribute eigrp 100
!
router eigrp 100
 redistribute ospf 1

In this example, the redistribute eigrp 100 command under the router ospf 1 configuration tells the router to take the routes it has learned from EIGRP (autonomous system 100) and redistribute them into OSPF (process ID 1). Similarly, the redistribute ospf 1 command under the router eigrp 100 configuration tells the router to take the routes it has learned from OSPF (process ID 1) and redistribute them into EIGRP (autonomous system 100).

It’s important to note that router redistribution requires careful planning and configuration, as it can introduce routing loops and other issues if not done correctly. It’s also common to use route filtering and route maps to control which routes are redistributed and how they are redistributed.

There are several security considerations and potential vulnerabilities associated with route redistribution in enterprise networking:

1. Routing Loops: Incorrectly configured route redistribution can lead to routing loops, where packets continuously circulate between routers without reaching their destination. This can cause network congestion and degrade network performance.
2. Suboptimal Routing: If route metrics are not properly adjusted during redistribution, it can lead to suboptimal routing paths. This can cause increased latency and reduced network efficiency.
3. Routing Table Pollution: Without proper filtering, route redistribution can introduce unnecessary or unwanted routes into the routing table, leading to increased memory and CPU usage on routers.
4. Security Risks: Redistribution can potentially introduce routes from less secure or untrusted networks into more secure or trusted networks. This can create a pathway for attackers to access sensitive areas of the network.
5. Control Plane Overload: Excessive route redistribution can overload the router’s control plane, leading to slower route processing and potentially causing instability in the network.

To mitigate these risks, it’s important to implement route redistribution carefully and with the following best practices:

• Use route filtering to control which routes are redistributed and to prevent unwanted routes from being introduced into the network.
• Adjust route metrics appropriately to ensure optimal routing paths and to prevent routing loops.
• Limit the scope of redistribution to only the necessary routing protocols and network segments.
• Regularly monitor and review the routing configuration to ensure that it remains secure and efficient.
• Implement network segmentation and access control to limit the potential impact of security risks associated with route redistribution.

By following these best practices, organizations can reduce the security risks and potential vulnerabilities associated with route redistribution in their enterprise networks.