Huawei Quidway S6500 Series Operation Manual page 229

Operation Manual - Routing Protocol
Quidway S6500 Series Ethernet Switches
Note:
CIDR handles IP addresses in an entirely new way, that is, it does not distinguish
networks of 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.
BGP runs on a router in any of the following modes:
Internal BGP (IBGP)
External BGP (EBGP)
The BGP is called IBGP when it runs in an AS and EBGP when it runs among different
ASs.
6.1.2 BGP Messages
BGP is driven by messages, which include the following types:
Type 1, OPEN: The first message sent after the creation of a connection to create
association between BGP peers.
Type 2, UPDATE: The most important information in BGP system used to
exchange routing information between peers. It is composed of up to three parts,
that is, unreachable route, path attributes and network layer reachable information
(NLRI).
Type 3, NOTIFICATION: Used to notify errors.
Type 4, KEEPALIVE: Used to check connectivity.
Type 5, ROUTE-REFRESH: Used to advertise its own route refreshing capability.
The first four types are defined in RFC1771, while the last one is in RFC2918 (Route
Refresh Capability for BGP-4).
6.1.3 BGP Routing Mechanism
On the first startup of the BGP system, the BGP router exchanges routing information
with its peers by transmitting the complete BGP routing table, after that only update
messages are exchanged. In the operating of the system, keepalive messages are
received and transmitted to check the connections between various neighbors.
Huawei Technologies Proprietary
6-2
Chapter 6 BGP Configuration