Establish basic BGP neighbor relationships
The BGP equivalence between two routers is accomplished in two steps:
- Establish the bgp process with the router bgp command and clarify the local AS address.
- Use the neighbor remote-AS command to determine the neighbor and the neighbor’s AS Address.
Establishing a neighbor relationship by using the IP address of the end-to-side physical interface is the most basic and simplest configuration of the BGP, but this configuration does not provide redundancy.
Build neighbors through loopback interfaces
This configuration provides redundancy and the only requirement is connectivity between the loop-back interfaces. If there are multiple paths between two routers that establish a neighbor relationship, then we can use the loopback interface of each router to build a neighbor relationship to provide better performance, Not only is the loopback interface more stable than the physical interface, but more importantly provides redundancy, when one of the links breaks down, this does not affect the BGP routing protocol to establish neighbor relationships.
Route notification into BGP
To notify the target network through the BGP protocol, you must first inject the routing entries into the BGP. There are three methods:
（1）Redistributing the routing entries learned from the IGP into the BGP;
（2）The network is declared into the BGP by network command;
（3）The network is declared into BGP by adding static routing entries and then using the network command.
How to Notify a BGP Neighbor to a Default Route
In total, there are three ways to notify the BGP end-to-end of a default routing.
（1）If the default route is notified only to a specific counterpart, it can be done through the neighbor default-originate command, which can be implemented with or without the default route in the local routing table.
（2）If a default route is sent to all the BGP neighbors, we must go through three steps to complete this task. First, create a default route to NULL 0, then redistribute it to the BGP process, and finally, use the default-information originate command in the BGP process.
（3）The routing entry to NULL 0 is first established in the IGP table and notified using the network command.
BGP routing summary
Routing summary can be achieved in two ways:
（1）By adding a static route entry to NULL 0, and then notifying it through the network command.
（2）generating a summary route by using command aggregate-address.
In this approach, by default, aggregation is notified to the opposite end along with the specific route, and by using the keyword summary-only, only the summary route is notified and the specific route is suppressed.