So what is BGP? In this series of posts I will be explaining the main principles of BGP. BGP–Border Gateway Protocol–is the de facto core routing protocol of the Internet. It operates by exchanging routes among Internet Autonomous Systems, and it is considered a path vector protocol. Routing is performed by shortest path possible and according to network policies within each Autonomous System. Most large service providers use BGP, and enterprises can operate BGP internally to influence metrics.

BGP operates in Layer 4 of the OSI network model and establishes TCP connections via port 179 between neighbors. BGP that is used internally is designated as iBGP and when used externally it is designated as eBGP. The implementation of routing policies are done mainly by route maps. For example, influencing traffic with BGP policies can be done with the MED (Multi-Exit Discriminator) attribute, which tells a remote AS that a specific entry into an AS is the preferred one. Therefore, BGP is great for multi-homing to different ISPs (in terms of load balancing and backup).

ISPs that run BGP also integrate Multiprotocol BGP (MP-BGP). It is a special extension of BGP that works with MPLS, which allows service providers to offer businesses VPN capabilities and secure connectivity across multiple branches.

This technology is very widespread in large-scale enterprises. Proactive monitoring and fault resolution of BGP is essential due to its importance and influence on the topology.

Smart BGP signatures are already embedded into indeni and many others are planned.

Here are several examples for checks indeni has around BGP configuration:

• BGP Neighbor Is Down – indeni will alert when neighbors appear to be down in neighbors tables.
• BGP Neighbor State Has Changed – indeni will alert when the state has changed for any BGP peers or neighbors in the peer/neighbor table.
• Some Network Summarizations Are Too Loose – indeni will verify that network summarizations are not too loose, and that they do not contain unreachable networks.
• Internal Devices Given an External IP – indeni will alert if a public IP address has been used in an internal network.