Learning Center / What is BGP? What is BGP (Border Gateway Protocol)? Border Gateway Protocol (BGP) is the routing protocol that keeps the global Internet connected. It coordinates how independent networks exchange rout…

What Is BGP (Border Gateway Protocol)? How It Works, Use Cases & Security

Last updated: April 2026
Reading time: ~7 min
Audience: Boxis customers and administrators.

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Learning Center / What is BGP?

# What is BGP (Border Gateway Protocol)?

Border Gateway Protocol (BGP) is the routing protocol that keeps the global Internet connected.
    It coordinates how independent networks exchange routing information so that data can find the
    best path from source to destination.

BGP
    Internet routing
    Networking
    Border Gateway Protocol

                ## On this page

                - [What is BGP?](#what-is-bgp)

• Why is BGP important?
• Core BGP concepts
• How BGP works
• Types of BGP: iBGP vs eBGP
• Benefits of using BGP
• BGP challenges and security
• Common BGP use cases
• BGP and cloud networking

• FAQ: BGP in brief

          Every time you visit a website, stream a video or use a cloud application, your data
              travels across multiple independent networks. BGP is the protocol that allows these
              networks to communicate with one another and decide which path traffic should take.
  
          In this article, we explain **what BGP is**, **how it works**,
              the difference between **iBGP and eBGP**, and the main
              **use cases and security considerations** for modern infrastructures.
  
          ## What is BGP?
  
          **Border Gateway Protocol (BGP)** is a standardised routing protocol used to
              exchange reachability information between large networks called
              **Autonomous Systems (AS)** on the Internet.
  
          BGP allows networks to:
  
          - Announce which **IP prefixes** (IP address ranges) they can reach

• Learn paths to distant networks through their neighbours

• Apply routing policies to choose the preferred path

          Because nearly all interconnection between ISPs, cloud providers and large enterprises
              relies on BGP, it is often described as the
              **“routing protocol of the Internet”**.
  
          ## Why is BGP important for the Internet?
  
          BGP is essential because it transforms thousands of independent networks into a single,
              globally reachable Internet.
  
          ### Global reachability
  
          Each Autonomous System announces the IP prefixes it can deliver traffic to. BGP propagates
              these announcements across the Internet so that routers can build a global routing table
              and deliver packets to almost any destination.
  
          ### Network stability
  
          When a link fails or a network goes offline, BGP updates the routes and converges towards
              an alternative path. This dynamic behaviour helps to maintain service availability and
              avoid large-scale outages.
  
          ### Traffic engineering
  
          BGP is a **policy-based** protocol. Network operators can adjust preferences
              to:
  
          - Use low-latency paths for critical applications

• Avoid expensive or congested links

• Distribute traffic across multiple providers

          ## Core BGP concepts
  
          ### Autonomous Systems (AS) and AS numbers
  
          An **Autonomous System (AS)** is a group of IP networks and routers under a
              single administrative control, such as an ISP, a cloud provider or a large enterprise.
              Each AS is identified by an **Autonomous System Number (ASN)**, assigned by a
              regional Internet registry.
  
          ### IP prefixes and routes
  
          A **BGP route** describes how to reach a specific IP prefix, such as
              `203.0.113.0/24`. Each route contains:
  
          - The destination IP prefix

• The AS path (the sequence of ASNs the route has traversed)

• Additional attributes used in path selection

          ### Key BGP attributes
  
          When multiple routes exist for the same prefix, BGP uses attributes to select the best
              path. Common attributes include:
  
          - **AS_PATH** – the list of ASNs a route has passed through

• LOCAL_PREF – local preference value inside an AS
• MED (Multi-Exit Discriminator) – suggests a preferred entry point

• Communities – tags used to apply flexible policy rules

          ## How does BGP work?
  
          BGP peers (also called neighbours) are configured manually between routers. They establish
              a TCP session, usually on port 179, and then exchange routing information.
  
          The basic steps are:
  
          1. **Session establishment** – two routers open a TCP connection and exchange BGP *OPEN* messages.

  2. Initial table exchange – each router sends the routes it knows to its neighbour.
  3. Path selection – the router compares all available routes for each prefix and selects a single best path, based on attributes and local policies.
  4. Routing table update – the best path is installed in the forwarding table so traffic can be sent to the chosen next hop.

  5. Incremental updates – after the initial exchange, only changes (new routes, modified attributes, withdrawals) are sent.

         ## Types of BGP: iBGP vs eBGP
     
         ### External BGP (eBGP)
     
         **eBGP** is used **between different Autonomous Systems**.
             Typical examples include:
     
         - Between an ISP and a customer network

• Between two ISPs at an Internet Exchange Point

• Between a cloud provider and a transit provider

          ### Internal BGP (iBGP)
  
          **iBGP** is used **inside a single AS**. It distributes routes
              learned via eBGP (or from other internal routers) throughout the AS so all edge routers
              have a consistent view of external destinations.
  
          Large networks often combine iBGP with an interior gateway protocol (such as OSPF or IS-IS)
              that provides internal reachability information.
  
          ## Benefits of using BGP
  
          - **Scalability:** designed to handle hundreds of thousands of routes.

• Policy control: fine-grained control over inbound and outbound traffic.
• Redundancy: support for multi-homing with multiple ISPs.

• Flexibility: easy integration with VPNs, data centres and cloud networks.

          ## BGP challenges and security risks
  
          BGP was designed in a more trusted phase of the Internet and has limited built-in
              security. Misconfigurations or malicious announcements can have a global impact.
  
          ### BGP hijacking
  
          **BGP hijacking** occurs when a network improperly announces IP prefixes it
              does not own. Traffic can then be redirected, intercepted or dropped.
  
          ### Route leaks
  
          A **route leak** happens when routes learned from one peer or provider are
              mistakenly advertised to another, violating routing policy and potentially causing
              sub-optimal paths or outages.
  
          ### Best practices to secure BGP
  
          - Apply strict **route filters** per neighbour

• Use RPKI and route origin validation where possible
• Set max-prefix limits to protect against route table floods

• Monitor BGP announcements and paths for anomalies

          ## Common BGP use cases
  
          ### Multi-homing with multiple ISPs
  
          Organisations that require high availability often connect to two or more ISPs and use BGP
              to maintain Internet connectivity even if one provider fails.
  
          ### Traffic engineering and load balancing
  
          With techniques such as AS path prepending, MEDs and BGP communities, operators can steer
              traffic over preferred links and balance loads across different connections.
  
          ### Data centre and cloud interconnection
  
          Cloud providers, content delivery networks and data centre operators rely on BGP to connect
              multiple sites, peer with other networks and implement anycast routing for distributed services.
  
          ## BGP and modern cloud networking
  
          In cloud and hosting environments, BGP is commonly used at the network edge to connect data
              centres to the Internet, to build private interconnects and to secure redundant VPN or SD-WAN
              topologies.
  
          Understanding how BGP policies influence routing decisions helps you optimise latency,
              availability and resilience for your applications.
  
          ## FAQ: BGP in brief
  
          ### What is BGP in simple terms?
  
          BGP is like a global navigation system for the Internet. It tells large networks which paths
              to use so that data can travel from one network to another.
  
          ### Is BGP the same as OSPF?
  
          No. **OSPF** is an interior gateway protocol used inside a single organisation’s
              network. **BGP** is an exterior gateway protocol used between different networks
              (ISPs, cloud providers, enterprises) on the global Internet.
  
          ### Do small businesses need BGP?
  
          Most small businesses that use a single ISP and private addressing do not need BGP. BGP
              becomes relevant when you have your own public IP ranges, an ASN or multiple upstream providers.
  
          ### Is BGP secure?
  
          BGP itself does not offer strong security features. It should be combined with
              authentication on BGP sessions, strict filtering, RPKI and continuous monitoring to reduce
              the risk of hijacks and route leaks.
  
              ### Related topics
  
              - [What is IP routing?](/en/learn/what-is-routing/)

• What is an Autonomous System?
• What is anycast?

• What is network peering?

              ### Need BGP-ready connectivity?
  
              Contact our team to discuss IP transit, colocation and cloud connectivity options
                  tailored to your infrastructure.
  
              [Contact sales](/en/contact/)

Expected result

• The product behaves as described in each step (connectivity, message, or UI state).

If something goes wrong

• Repeat the step and check for typos (hostnames, passwords, ports).
• Note the exact error message or screenshot.
• Open a ticket in the Boxis client area with the service name, time of the test, and any trace (e.g. traceroute) if it is a network issue.

See also

• Other articles in the same category in the Boxis knowledge base.
• /knowledgebase/ — main knowledge base index.