H3C S9500 Series Operation Manual

Also see for S9500 Series: Operation manual Operation manual Operation manual Operation manual Operating manual

Contents

Operation Manual – Routing ProtocolH3C S9500 Series Routing Switches Chapter 6 BGP Configuration6-1Chapter 6 BGP Configuration6.1 BGP/MBGP Overview6.1.1 Introduction to BGPBorder gateway protocol (BGP) is an inter-autonomous system (inter-AS) dynamicroute discovery protocol. Three early versions of BGP are BGP-1 (RFC1105), BGP-2(RFC1163) and BGP-3 (RFC1267). The current version is BGP-4 (RFC1771) that isapplied to advertised structures and supports classless inter-domain routing (CIDR).Actually, BGP-4 is becoming the external routing protocol standard of the Internet,which is frequently used between ISPs.The characteristics of BGP are as follows:z BGP is an external gateway protocol (EGP). Different from such internal routingprotocols as OSPF and RIP, it focuses on route propagation control and selectionof best routes other than discovery and calculation of routes.z It eliminates routing loop by adding AS path information to BGP routes.z It enhances its own reliability by using TCP as the transport layer protocol.z When routes are updated, BGP only transmits updated routes, which greatlyreduces bandwidth occupation by route propagation and can be applied topropagation of a great amount of routing information on the Internet.z BGP-4 supports CIDR, which is an important improvement to BGP-3.z In consideration of management and security, users desire to perform control overoutgoing and incoming routing information of each AS. BGP-4 provides abundantroute policies to implement flexible filtering and selecting of routes.z BGP-4 can be extended easily to support new developments of the network.Note:z CIDR handles IP addresses in an entirely new way, that is, it does not distinguishnetworks of Class A, Class B and Class C. For example, an invalid Class C networkaddress 192.213.0.0 (255.255.0.0) can be expressed as 192.213.0.0/16 in CIDRmode, which is a valid super network. Here /16 means that the subnet mask iscomposed of the first 16 bits from the left.z The introduction of CIDR simplifies route summary. Actually, route summary is theprocess of aggregating several different routes, which turns advertisementprocesses of several routes to the advertisement of single route so as to simplify therouting table.