Knowledge Base

What is a BGP Route Reflector (RR)?

A BGP Route Reflector (RR) is a solution in Border Gateway Protocol (BGP) networks that eliminates the full mesh requirement of iBGP (Internal BGP) sessions. In iBGP, all iBGP speaking routers must establish direct sessions with each other. In large networks, this leads to administrative complexity and resource consumption. This is where the Route Reflector comes into play.

The Route Reflector reflects routes learned from iBGP neighbors (clients) to other iBGP neighbors (clients and non-clients). This eliminates the need for each router to establish sessions with every other router and increases the scalability of the iBGP network.

The Route Reflector reflects the routes it receives without changing them. It can only add some changes to the route's attributes. These changes are used to indicate the source of the route and that it has been reflected.

Important Points:

• Eliminates the iBGP full mesh requirement.
• Increases network scalability.
• Reduces the number of sessions between routers.
• Simplifies management.

What are the Advantages of BGP Route Reflector?

BGP Route Reflector has many advantages:

1. Scalability: Its biggest advantage is that it significantly increases the scalability of iBGP networks. By eliminating the full mesh requirement, it makes it easier to add new routers to the network and manage existing routers.
2. Ease of Management: By reducing the number of sessions between routers, it simplifies network management. Configuring a Route Reflector is easier than configuring separate iBGP sessions on each router.
3. Resource Saving: Reduces the processing load on routers. Since each router does not need to establish sessions with all iBGP neighbors, CPU and memory usage is reduced.
4. Flexibility: Route Reflectors can be configured in different ways depending on the network topology. A single Route Reflector or multiple Route Reflectors can be used. In addition, redundancy can be provided between Route Reflectors.
5. Faster Convergence: Route Reflectors enable faster propagation of routes, leading to faster convergence time in the network.

Real-Life Example: An internet service provider (ISP) serves thousands of customers. There are hundreds of routers in this ISP's network. If iBGP full mesh were used, each router would have to establish sessions with all other routers. This would lead to an administrative nightmare and resource waste. By using Route Reflector, the ISP has solved this problem and managed its network more efficiently.

What is a Route Reflector Client and Non-Client?

There are two basic router types in a Route Reflector topology:

• Route Reflector Client: These are routers that establish an iBGP session with the Route Reflector and learn routes from the Route Reflector. Clients do not reflect the routes they learn to other Clients. This is the basic function of the Route Reflector.
• Route Reflector Non-Client: These are routers that establish an iBGP session with the Route Reflector but are not Clients. Non-Clients reflect the routes they learn to other Non-Clients and Clients. Usually, the core routers of the network are configured as Non-Clients.

Schema Description: The following schema shows the relationship between a Route Reflector (RR), Clients (C), and Non-Clients (NC).

     NC --- RR --- NC
      \   /  \   /
       C    C    C

In this schema, the Route Reflector (RR) has established iBGP sessions with both Non-Clients (NC) and Clients (C). Clients only send the routes they learn to the RR. Non-Clients send the routes they learn to the RR and other Non-Clients. The RR reflects the routes it receives to both Clients and Non-Clients.

What is Route Reflector Clustering and Why is it Used?

Route Reflector clustering is when multiple Route Reflectors work together to provide higher redundancy and scalability. Using a single Route Reflector can create a single point of failure. If the Route Reflector crashes, all Clients lose routes and network outages occur.

Route Reflector clustering is used to solve this problem. Multiple Route Reflectors share the same cluster ID, learning the routes reflected by each other. If one Route Reflector crashes, the other Route Reflectors take over its role and there is no network outage.

Step-by-Step Explanation:

1. Multiple Route Reflectors are configured.
2. Each Route Reflector is assigned the same cluster ID.
3. Route Reflectors establish iBGP sessions with each other.
4. When a Route Reflector learns a route from its Client, it adds its own cluster ID to the route.
5. When other Route Reflectors learn this route, they check the cluster ID in the route. If the cluster ID is the same as their own cluster ID, they do not reflect the route. This prevents routing loops.

Important Points:

• Provides redundancy.
• Increases scalability.
• Eliminates a single point of failure.
• Prevents routing loops.

Which Attributes are Used in Route Reflector?

Route Reflector uses some BGP attributes when reflecting routes. These attributes are used to indicate the source of the route and that it has been reflected.

• ORIGINATOR_ID: Contains the Router ID of the router that first announced the route. This attribute is used to prevent routing loops. When a Route Reflector reflects a route, it adds its own Router ID to the route as ORIGINATOR_ID. If a router learns a route with an ORIGINATOR_ID that is its own Router ID, it ignores the route.
• CLUSTER_LIST: Contains a list of Route Reflector clusters that the route has passed through. This attribute is also used to prevent routing loops. When a Route Reflector reflects a route, it adds its own cluster ID to the CLUSTER_LIST. If a Route Reflector learns a route with its own cluster ID in the CLUSTER_LIST, it ignores the route.

Code Example (Cisco IOS):

router bgp 65000
 bgp router-id 1.1.1.1
 neighbor 2.2.2.2 remote-as 65000
 neighbor 2.2.2.2 update-source Loopback0
 neighbor 2.2.2.2 route-reflector-client
!

In this example, the router with Router ID 1.1.1.1 is a BGP router in AS 65000. The neighbor router with IP address 2.2.2.2 is configured as a Route Reflector client.

How to Configure Route Reflector? (Step-by-Step Instructions)

Route Reflector configuration may vary depending on the router brand and model used. However, the following steps are generally followed:

1. BGP Configuration: First, BGP must be configured on the router. This includes assigning the Router ID, determining the AS number, and defining iBGP neighbors. For more information on this topic, you can visit our BGP Configuration page.
2. Route Reflector Client Configuration: It is determined which of the iBGP neighbors will be Route Reflector clients. These routers are introduced to the Route Reflector with the "route-reflector-client" command.
3. Cluster ID Configuration (If Necessary): If more than one Route Reflector is used, each Route Reflector is assigned the same cluster ID. This is necessary to prevent routing loops.
4. Policy Configuration (If Necessary): It is determined which routes the Route Reflector will reflect and which routes it will filter. This can be done using route-maps and prefix-lists.
5. Verification: After the configuration is complete, it should be verified that the Route Reflector is working correctly. This can be done using the "show ip bgp summary" and "show ip bgp" commands.

Code Example (Cisco IOS):

! Route Reflector Configuration
router bgp 65000
 bgp router-id 1.1.1.1
 neighbor 2.2.2.2 remote-as 65000
 neighbor 2.2.2.2 update-source Loopback0
 neighbor 2.2.2.2 route-reflector-client
!

! Client Configuration
router bgp 65000
 bgp router-id 2.2.2.2
 neighbor 1.1.1.1 remote-as 65000
 neighbor 1.1.1.1 update-source Loopback0
!

In this example, the router with the IP address 1.1.1.1 is configured as a Route Reflector. The router with the IP address 2.2.2.2 is configured as a client of this Route Reflector.

How to Provide Redundancy Between Route Reflectors?

The most common method to provide redundancy between Route Reflectors is to use multiple Route Reflectors. These Route Reflectors learn the routes reflected by each other by sharing the same cluster ID. If one Route Reflector fails, the other Route Reflectors take over its role and there is no interruption in the network.

Redundancy Provisioning Methods:

• Clustering: Multiple Route Reflectors work together by sharing the same cluster ID.
• Route Reflector Groups: Route Reflectors can be configured in groups. If one of the Route Reflectors in a group fails, the others automatically take over.
• BGP Multipath: BGP supports learning multiple paths to the same destination. Route Reflectors can provide redundancy by reflecting different paths to the same destination.

Important points:

• Redundancy increases the reliability of the network.
• Minimizes downtime.
• Ensures the continuity of the network.

What Should Be Considered When Using Route Reflector?

There are some important points to consider when using Route Reflector:

• Correct Planning: Where the Route Reflector will be placed, how many Route Reflectors will be used, and which routers will be clients should be carefully planned.
• Cluster ID Management: If multiple Route Reflectors are used, ensure that the cluster IDs are configured correctly. Incorrectly configured cluster IDs can lead to routing loops.
• Policy Configuration: Which routes the Route Reflector will reflect and which routes it will filter should be carefully configured. Incorrect policy configuration can lead to undesirable consequences in the network.
• Resource Monitoring: Route Reflectors can increase the traffic load on the network. Therefore, the CPU, memory, and bandwidth usage of Route Reflectors should be monitored regularly.
• Security: Route Reflectors are a critical part of the network. Therefore, the security of Route Reflectors must be ensured. Firewalls and access control lists (ACLs) should be used to prevent unauthorized access.

Case Study: A financial institution has a large network infrastructure. This network includes multiple data centers and hundreds of branches. Using iBGP full mesh is not possible in this network. By using Route Reflector, the financial institution has made its network more scalable and manageable. However, incorrect configuration of Route Reflectors has led to routing loops and network outages. Therefore, the financial institution reviewed the Route Reflector configuration and ensured correct configuration.

The following table compares the advantages and disadvantages of Route Reflector:

Finally, it is of great importance that the Route Reflector is positioned appropriately in the network topology. Incorrect positioning can negatively affect performance.

The following table summarizes different Route Reflector topologies and usage scenarios: