3Com Switch 8800 Family Configuration Guide

540 CHAPTER 49: BGP/MPLS VPN CONFIGURATION
By default, no VPN-instance is defined.
1 Configure RD for the vpn-instance
After PE router is configured with RD, when a VPN route learned from CE is
imported into BGP, BGP attaches the RD in front of the IPv4 address. Then the
general IPv4 address which may overlaps between several VPN IPv4 addresses in
the VPN is turned into a globally unique VPN IPv4 address and thus ensure the
correct routing in the VPN.
Perform the following configuration in VPN-instance view.
The parameter in the above command has no default value. A VPN-instance works
only when a RD is configured for it. Other parameters for a VPN-instance cannot
be configured before configuring a RD for it.
To modify the RD, you must first delete the VPN-instance and reconfigure it.
2 Configure VPN-instance description
Perform the following configuration in VPN-instance view
3 Configure VPN-target attribute for the VPN-instance
VPN-target attribute, a BGP extension community attribute, controls
advertisement of VPN routing information.
The following is the advertisement controlling process of VPN routing information:
■ When BGP is imported into a VPN route learned at CE, it associates a
VPN-target extension community attribute list for the route. Usually the list is
the VPN-instance output routing attribute list which is associated with CE.
■ VPN instance defines input routing attribute list according to the
import-extcommunity in VPN-target, defines the acceptable route range and
import it.
■ VPN instance modifies VPN-target attributes for the routes to be advertised,
according to the export-extcommunity in VPN-target.
Like an RD, an extension community includes an ASN plus an arbitrary number or
an IP address plus an arbitrary number. There are two types of formats:
The first one is related to autonomous system number (ASN), in the form of 16-bit
ASN (can be 0 here): 32-bit user-defined number, for example, 100:1.
Tabl e 526 Configure RD for the VPN-instance
Operation Command
Configure RD for the VPN-instance route-distinguisher route-distinguisher
Tabl e 527 Configure VPN-instance description
Operation Command
Configure VPN-instance description description vpn-instance-description
Delete VPN-instance description undo description