Switch 7700 Configuration Guide, v2

BGP 117
[Switch C-Vlan-interface101] isis enable
[Switch C] interface vlan-interface 100
[Switch C-Vlan-interface100] isis enable
4 Configure Switch D
[Switch D] isis
[Switch D-isis] network-entity 86.0001.0000.0000.0008.00
[Switch D] interface vlan-interface 102
[Switch D-Vlan-interface102] isis enable
[Switch D] interface vlan-interface 100
[Switch D-Vlan-interface100] isis enable
BGP Border Gateway Protocol (BGP) is an inter-AS dynamic route discovery protocol.
Three early versions of BGP are RFC1105 (BGP-1), RFC1163 (BGP-2) and RFC1267
(BGP-3). The presently used version is RFC1771 (BGP-4) that is applied to
distributed structures and supports Classless Inter-Domain Routing (CIDR). Besides,
it is also used to implement policies configured by users. Actually, BGP-4 is
becoming the actual external routing protocol standard of Internet, which is
frequently used between ISPs.
The characteristics of BGP are as follows:
■ BGP is an external routing protocol. Different from such internal routing
protocols as OSPF and RIP, it focuses on route propagation control and
selection of best routes other than discovery and calculation of routes.
■ Eliminating route loop completely by adding AS path information to BGP
routes.
■ Using TCP as transport layer protocol so as to enhance reliability of the
protocol.
■ BGP-4 supports CIDR, which is an important improvement to BGP-3. CIDR
addresses IP addresses in an entirely new way, that is, it does not divide
networks into Class A, Class B and Class C. For example, an invalid Class C
network address 192.213.0.0 (255.255.0.0) can be expressed as
192.213.0.0/16 in CIDR mode, which is a valid super network. Here /16 means
that the subnet mask is composed of the first 16 bits from the left. The
introduction of CIDR simplifies route aggregation. Actually, route aggregation
is the process of aggregating several different routes, which turns
advertisement processes of several routes to the advertisement of single route
so as to simplify the routing table.
■ When routes are updated, BGP only transmits incremental routes, which
greatly reduces bandwidth occupation by route propagation and can be
applied to propagation of great amount of routing information on Internet.
■ In consideration of management and security, users desire to perform control
over outgoing and incoming routing information of each AS. BGP-4 provides