Brocade Network OS Administrator’s Guide v4.1.1 - Manual (Page 617)

Configuring BGP
● BGP overview............................................................................................................... 617
● Understanding BGP configuration fundamentals.......................................................... 624
● Configuring BGP........................................................................................................... 636
BGP overview
Border Gateway Protocol (BGP) is an exterior gateway protocol that performs inter-autonomous system
(AS) or inter-domain routing. It peers to other BGP-speaking systems over TCP to exchange network
reachability and routing information. BGP primarily performs two types of routing: inter-AS routing, and
intra-AS routing. BGP peers belonging to different autonomous systems use the inter-AS routing,
referred as Exterior BGP (EBGP). On the other hand, within an AS BGP can be used to maintain a
consistent view of network topology, to provide optimal routing, or to scale the network.
BGP is a path vector protocol and implements this scheme on large scales by treating each AS as a
single point on the path to any given destination. For each route (destination), BGP maintains the AS
path and uses this to detect and prevent loops between autonomous systems.
The Open Shortest Path First (OSPF) protocol (supported in Network OS 3.0 and later) provides
dynamic routing within the VCS and internal domain. However, even though OSPF suffices for most of
the routing needs within the VCS, an exterior gateway protocol such as BGP is needed for inter-domain
routing outside the VCS domain.
BGP support
Support for BGP on Network OS platforms is for BGP4 (compliant with RFC 1771 and 4271), and
provides the following:
• Connectivity from the VCS to a core/external network or cloud
• A foundation to support virtual routing and forwarding (VRF) for multi-tenancy and remote-VCS
access and route distribution across VRFs
• A foundation to support VRF scaling (OSPF does not scale well with lots of VRFs)
• A foundation to support OSPF Interior Gateway Protocol (IGP) scaling needs in future
NOTE
An L3 License is required to enable BGP routing.
Deployment scenarios
BGP is typically used in a VCS Fabric at the aggregation layer and in connecting to the core. Routing
bridges at the aggregation layer can either connect directly to the core, or connect through an MLX. The
topologies below illustrate connectivity with and without an MLX. The details of these topologies are
discussed in subsequent sections.
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