QTECH
Software Configuration Manual
9-120
Chapter 9
BGP Configuration
9.1 Brief Introduction of BGP
BGP
（
Border Gateway Protocol
）
is a dynamic route protocol in anonymous system whose basic function is
automatically changing no-loop route information in AS and contructs topology from AS through changing network
layer arrival information with AS routine attribution.
The early published BGP standard document are RFC1105
（
BGP-1
）
,RFC1163
（
BGP-2
）
and RFC1267
（
BGP-3
）
. The RFC1771
（
BGP- 4
）
is commonly used and RFC4271
（
BGP- 4
）
is the latest edition which is suitable
for distributed structure and supports CIDR
（
Classless InterDomain Routing
）
. BGP can also be used in strategy of
carrying out user’s configuration. BGP-4 quickly becomes the real standard of Internet outer route protocol. BGP is
mostly used between ISP.
The specialty of BGP is as following:
BGP is an outer route protocol which is different from such inner route protocol as OSPF,RIP. It is used for
controlling route transmission and choosing better route, not searching and calculating route.
Completely solve route cycling through AS path information in BGP route.
Use TCP as tis transmission layer protocol to improve reliability.
BGP-4 supports CIDR, which is an important improvement of BGP-3. CIDR treats IP address without
classifying category A, B and C. The introduction of CIDR simplized Route Aggregation, which is the process of
combining different routes and several routes become one to reduce the resource uitilization and BGP cost.
When update route, BGP sends adding route to reduce the bandwidth of BGP broadcasting route to transmit
plenty of route information in internet.
For management and security, BGP-4 provides abundant route strategy to realize agile filtration and choice.
BGP operates in s specific router as a high layer protocol. BGP router exchanges route information through
sending whole BGP table and handle route changes through Update message. Sending and receiving keepalive to
detect the connection.
The router sending BGP message is called BGP speaker which receives and generates new route
information and send advertise to pther BGP speaker. When others receiving the new advertising, this route is better
than the current one, or it hasn’t received the route, this new advertising will be broadcasted to all other BGP speakers
and the BGP speaker who changes the message to others is called peer.
BGP runs in router with following two ways:
IBGP
（
Internal BGP
）
EBGP
（
External BGP
）
When running in the internal of the same AS, it is called IBGP
；
when running in different AS, is called
EBGP.
BGP runs through message. The message can be divided into 4 kinds:
Open message
Update message
Notification message
Keepalive message
Open message is the first message after TCP connection, which is used to set up the relationship between
BGP and peer. Notification message is error notification message. Keepalive message is used to detect the efficiency
of connection. Update message is the mpst important message for exchanging route information. Update message
consists of unreachable route, path attributes and NLRI
，
Network Layer Reachability Information.
9.2 BGP Configuration
BGP Configuration list
BGP Configuration list is as following:
l
Enable/disable BGP
l
Specify the network route BGP to be notified
