BGP manages BGP peering policies through the use of BGP attributes that are used to define the characteristics and preferences of each peering session. These attributes include:
1. Autonomous System (AS) Path: BGP uses the AS Path attribute to track the path that a packet takes through the network. This attribute is used to prevent loops and to avoid congested links.
1. Weight: The weight attribute is used to select the best path among multiple possible paths to a destination. The BGP router with the highest weight value is usually selected as the primary path.
1. Local Preference: The Local Preference attribute is used to indicate the preferred egress point for outbound traffic within an AS. The higher the value of this attribute, the more preferred the path.
1. Community: Communities are used to group BGP peers based on common characteristics, such as geographical location or business relationship. This attribute is used for filtering and route selection.
1. MED (Multi-Exit Discriminator): The MED attribute is used to influence the selection of the exit point from an AS to an external network. Peers can manipulate the MED attribute to prefer one exit point over another.
1. Route Maps: Route maps are used to filter or change BGP network route advertisements. They provide a flexible way to customize routing policies.
BGP peering policies are managed by configuring these attributes and applying them to specific BGP neighbors or groups of BGP peers. The configuration process is typically done on a per-router basis and must be coordinated with upstream and downstream peers to ensure consistent routing policies across the network.
