BGP (Border Gateway Protocol)

We host a full BGP routing table for our IP transit redundancy Border Gateway Protocol (BGP) is a set of rules and procedures that help an autonomous system (AS) exchange routing information over the internet. An AS is a network of computers run by organizations, controlling a range of IP addresses.

Every AS manages a table containing all its known routes to other networks, which is then propagated to neighboring systems (a.k.a., peers). The BGP decision-making mechanism analyses the data and selects the best route for the next network hop.


BGP benefits in controlling how traffic enters the local AS, rather than how traffic exits it. There are over 100,000 routes on the internet, and interior routers should not be overloaded unnecessarily. BGP should be used under the following circumstances:

  • Multiple connections exist to external AS via different providers.
  • Multiple connections exist to external AS through the same provider but connect separately through routing policy.
  • The existing routing equipment can handle the additional demands.

BGP is not a necessity when multiple connections to the internet are required; fault detection and redundancy of outbound traffic can easily be handled by OSPF or EIGRP. BGP is also unnecessary if there is only one connection to an external AS, such as the internet.

Why does your business need BGP?

  • Internet service advantages:
    BGP is a must if you are an ISP provider. Those ISPs who are consumer-focussed and tried to use BGP solely to peer with their upstream ISPs, but they eventually had to deploy BGP to increase the stability of their network, provide end-to-end quality-of-service or penetrate enterprise markets. Enterprise-focused ISPs have to run BGP from the start to support their multi-homed customers.
  • Layer 3 VPN services
    There are a variety of latest technologies used to implement Layer 3 VPN services in recent years, and MPLS-based VPNs have proven to be the most effective solution, partly due to using BGP as the underlying routing protocol. Fortunately, you don't have to deploy BGP everywhere in your network if you want to implement MPLS/VPN solutions.
    It's enough to use BGP on the Provider Edge (PE) routers that connect your VPN customers and on devices that act as route servers. These devices are not for heavy traffics; thus, they should not be expected to forward heavy traffic loads.
  • Increasing network stability
    BGP design should rely on another fast routing protocol OSPF, EIGRP, or IS-IS to provide core routing in the network, along with BGP for the edge/customer routing. With the separation of core and edge routing into two routing protocols, the network core becomes more stable, as the edge problems cannot disrupt the core.
    This design has been used very successfully in the Gotel Telecom network with haphazard addressing schemes that defy attempts at route summarization. Customers' routes should never be carried in the core routing protocol, as the customer's internal problems could quickly affect the stability of the network.
  • Automatic Response to Denial-of-Service Attacks
    BGP allows specifying IP address as the next-hop for an IP prefix. This property is often used to ensure optimum routing across a BGP autonomous system. You can also use it to implement network-wide sinkholes and remote blackholes to stop worms and denial-of-service attacks on your network quickly.
    Please note that you don't have to migrate your routing to BGP if you want to use these mechanisms. To implement remote blackholes, it's enough that you deploy BGP on strategic points in your network and link them via BGP sessions with a central router through which you'll insert the IP addresses to block.
  • Large-scale QOS or web caching deployment
    BGP not only carries many attributes describing the IP routes, but it also allows you to add extra load to every Internet Protocol route in the form of BGP communities. Those that are transparent to BGP unless you configure them manually with route selection rules to use them.
    Few technologies allow you to use these attributes to implement large-scale designs. BGP (QPPB) enables you to set Quality of Service bits for specified BGP destinations based on BGP communities and other BGP attributes. Similarly, you can also control the Web Cache Communication Protocol-based web caching policy with BGP.
Key Features
  • Shortest Autonyms System Path

    Selects an AS path which shows the number of AS hops to reach a given point, for each route. This selection criterion chooses the shortest AS path, i.e., the path with the lesser hops.

  • Lowest Origin Type

    Provide a higher preference to Exterior Gateway Protocol (EGP) as compared to Interior Gateway Protocol (IGP).

  • Lowest Multi-Exit Discriminator (MED)

    Tells about the preferred route for entering an AS, to other routers.

  • Lowest IGP Metric

    Chooses the path with the low Interior Gateway Protocol metric for the next hop.

  • Multiple Paths

    Indicates if multiple routes need to be installed in the routing table.

  • External Paths

    Selects the first received path out of all external paths.

  • Lowest Router ID

    Selects the path with the lowest router ID to the external BGP router.

  • Minimum Cluster List

    BGP selects the path with minimum cluster list length. If more than one path has the same router ID.