Brocade Communications Systems Layer 3 Routing Configuration ICX 6650 - Manual (Page 300)

282 Brocade ICX 6650 Layer 3 Routing Configuration Guide
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BGP4 overview
BGP4 overview
Border Gateway Protocol 4 (BGP4) is the standard Exterior Gateway Protocol (EGP) used on the
Internet to route traffic between Autonomous Systems (AS) and to maintain loop-free routing. An
autonomous system is a collection of networks that share the same routing and administration
characteristics. For example, a corporate intranet consisting of several networks under common
administrative control might be considered an AS. The networks in an AS can but do not need to
run the same routing protocol to be in the same AS, nor do they need to be geographically close.
Routers within an AS can use different Interior Gateway Protocols (IGPs) such as RIP and OSPF to
communicate with one another. However, for routers in different autonomous systems to
communicate, they need to use an EGP. BGP4 is the standard EGP used by Internet routers and
therefore is the EGP implemented on Brocade Layer 3 switches.
Figure 25 on page 282 shows a simple example of two BGP4 autonomous systems. Each AS
contains three BGP4 switches. All of the BGP4 switches within an AS communicate using IBGP.
BGP4 switches communicate with other autonomous systems using EBGP. Notice that each of the
switches also is running an Interior Gateway Protocol (IGP). The switches in AS1 are running OSPF
and the switches in AS2 are running RIP. Brocade Layer 3 switches can be configured to
redistribute routes among BGP4, RIP, and OSPF. They also can redistribute static routes.
FIGURE 25 Example BGP4 autonomous systems
Relationship between the BGP4 route table and
the IP route table
The Brocade Layer 3 switch BGP4 route table can have multiple routes to the same destination,
which are learned from different BGP4 neighbors. A BGP4 neighbor is another switch that also is
running BGP4. BGP4 neighbors communicate using Transmission Control Protocol (TCP) port 179
for BGP communication. When you configure the Brocade Layer 3 switch for BGP4, one of the
configuration tasks you perform is to identify the Layer 3 switch BGP4 neighbors.
AS 1 AS 2
EBGP
IBGP
OSPF
OSPF
IBGP
IBGP
OSPF
RIP
RIP RIP
IBGP
IBGP
IBGP
BGP4 Switch BGP4 Switch
BGP4 Switch BGP4 Switch BGP4 Switch BGP4 Switch