Zte ZXR10 GER, Руководство пользователя

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ZXR10 GER (V2.6.03) General Excellent Router User Manual Volume-I
228 Confidential and Proprietary Information of ZTE CORPORATION
BGP Overview
Border Gateway Protocol (BGP) is an inter-domain routing
protocol used among ASs, to exchange network reachability
information among ASs running the BGP. The information is a
list of ASs where a route passes, which is sufficient to set up a
diagram indicating the connection status of the ASs. Thus,
routing policy based on ASs is possible, and also the route
loopback problem is solved.
BGP of version 4 (BGP4) is the latest BGP version, which is
defined in RFC1771. BGP4 supports the implementation of CIDR,
supernet and subnet and the functions such as route
aggregation and route filtering. At present, BGP4 has found wide
application on the Internet.
An administrative area with independent routing policy is called
an Autonomous System (AS). An important feature of an AS is
that there is a unified internal route for another AS and has
consistent topology for a reachable destination. The indicator for
an AS is a 16-bit value, ranging from 1 to 65535. Where, 1
through 32767 are assignable, 32768 through 64511 are
reserved, and 64512 through 65534 are used for private ASs
(similar to private network addresses among IP addresses).
A session set up between BGP routers in different ASs is called
an EBGP session, while a session established between BGP
routers in the same AS is called an IBGP session.
BGP runs on a reliable transmission protocol. TCP is used as its
bottom-layer protocol, and the TCP port is port 179. Two routers
running BGP first set up a TCP connection, and then pass packet
authentication and exchange all the routing table information.
After that, when the route changes, the routers will send a
routing update message to all BGP neighbors, and then the BGP
neighbors will flood the routing information until the entire
network receives the routing information.
When a router sends BGP update messages about the
destination network to its peer router, the messages contain
information about BGP metric (called path attribute). The path
attribute is divided into four independent types:
„
Accepted and compulsory attributes: The attributes need
to appear in route description.
f
AS-path
f
Next-hop
f
Origin
„
Accepted and self-determined attributes: The attributes
do not have to appear in route description.
f
Local preference
f
Atomic aggregate
Definition
Version
Autonomous
System
EBGP & IBGP
Transmission
Protocol
Path Attribute