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BG (Border Gateway)

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Introduction:

Border Gateway (BG) is a device that connects different autonomous systems (AS) to exchange routing information between them. The BG device is usually a router that sits on the border of two ASs and acts as a gateway for the traffic between them. The main function of BG is to route packets between different ASs using the best path available. This article will discuss BG in detail, including its functions, types, and protocols used.

Functions of Border Gateway:

  1. Inter-AS routing: BG is primarily used to connect different ASs to exchange routing information. When a packet arrives at BG from one AS, it checks the routing table to find the best path to the destination AS. If the destination AS is not directly connected, the BG forwards the packet to the next hop that is closer to the destination AS. This process continues until the packet reaches the destination AS.
  2. Policy enforcement: BG also enforces policies that are defined by the AS administrators. These policies can be used to control the flow of traffic between ASs. For example, an AS may want to limit the amount of traffic it receives from another AS. In this case, the BG can be configured to drop packets that exceed a certain threshold.
  3. Security: BG is also used to provide security for the ASs. It can filter out packets that are not authorized to enter the ASs. For example, an AS may want to block packets from a certain IP address or block certain types of traffic. BG can be configured to perform these tasks.

Types of Border Gateway:

  1. External BG: External BG is used to connect different ASs. It is located at the border of the ASs and is responsible for exchanging routing information between them. External BG is also responsible for enforcing policies and providing security for the ASs.
  2. Internal BG: Internal BG is used to connect different subnets within the same AS. It is located within the AS and is responsible for routing traffic between the subnets. Internal BG is not responsible for exchanging routing information with other ASs.
  3. Virtual BG: Virtual BG is a software-based solution that emulates the functions of a physical BG. It is usually implemented on a server and can be used to connect different virtual networks.

Protocols used in Border Gateway:

  1. Border Gateway Protocol (BGP): BGP is the most commonly used protocol for exchanging routing information between different ASs. It is a path-vector protocol that is used to find the best path to the destination AS. BGP is a reliable protocol that provides a high level of control over routing policies.
  2. Open Shortest Path First (OSPF): OSPF is a link-state protocol that is used to exchange routing information within the same AS. It is used to find the best path to the destination subnet within the AS. OSPF is a fast protocol that provides a high level of scalability.
  3. Intermediate System to Intermediate System (IS-IS): IS-IS is a link-state protocol that is similar to OSPF. It is used to exchange routing information within the same AS. IS-IS is a scalable protocol that is commonly used in large networks.

Conclusion:

In conclusion, Border Gateway is a device that connects different autonomous systems to exchange routing information between them. It is responsible for routing packets between different ASs using the best path available. BG is also responsible for enforcing policies and providing security for the ASs. There are three types of BG: External BG, Internal BG, and Virtual BG. The most commonly used protocol for exchanging routing information between different ASs is BGP. OSPF and IS-IS are used to exchange routing information within the same AS.

The main advantage of BG is that it provides a high level of control over routing policies. This allows AS administrators to control the flow of traffic between different ASs and implement policies that suit their needs. BG also provides a high level of security by filtering out unauthorized traffic.