Basic Bgp Fundamentals; Figure 1: Bgp Fundamentals - Avaya 8000 Technical Configuration Manual

3. Basic BGP Fundamentals

There are two types of BGP connections, external BGP (EBGP) and internal BGP (IBGP). Routers
belonging to the same autonomous system (AS) and exchange BGP updates are referred to as running
IBGP. Routers that belong to a different AS and exchange BGP updates are referred to as running
EBGP. Within an AS, routers run an interior gateway protocol such as OSPF.
In Figure 1 shown below, the connections between Router-C in AS 40 to ERS 8000 switch 8008 and VSP
9000 switch 9001 in AS 20 are running EBGP. The connection between 8008 and 9001 is running IBGP.
To configure a router for basic BGP operations, the following parameters must be configured:

The Local AS number

The BGP Router ID
o
By default, the BGP Router ID will automatically use the OSPF Router ID. As BGP uses
the OSPF router ID, they cannot be different. A change in the router ID will require a BGP
restart to take effect.
o
It is recommended to use a loopback IP (also known as a circuitless IP or CLIP) address
for the OSPF Router-ID which in turn also becomes the BGP Router-ID. The CLIP
address can also be referred to as a loopback address. This IP address is used in BGP
Update messages. This will help for trouble-shooting purposes to give you an idea where
the updates are coming from.

The BGP neighbor peer(s) which can be iBGP or/and eBGP.
o
If iBGP, the remote-as will be the same
o
If eBGP, the remote-as will be different
For example, the following commands are used to configure BGP on ERS 8000 switch named 8008 and
VSP 9000 switch named 9001
January 2016

Figure 1: BGP Fundamentals

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