Figure 46: Overlapping Addresses Among Different VPNs
To avoid overlapping private addresses, you can configure the network devices to use
public addresses instead of private addresses. However, this is a large and complex
undertaking. The solution provided in RFC 4364 uses the existing private network numbers
to create a new address that is unambiguous. The new address is part of the VPN-IPv4
address family, which is a BGP address family added as an extension to the BGP protocol.
In VPN-IPv4 addresses, a value that identifies the VPN, called a route distinguisher, is
prefixed to the private IPv4 address, providing an address that uniquely identifies a private
IPv4 address.
Only the PE routers need to support the VPN-IPv4 address extension to BGP. When an
ingress PE router receives an IPv4 route from a device within a VPN, it converts it into a
VPN-IPv4 route by adding the route distinguisher prefix to the route. The VPN-IPv4
addresses are used only for routes exchanged between PE routers. When an egress PE
router receives a VPN-IPv4 route, it converts the VPN-IPv4 route back to an IPv4 route
by removing the route distinguisher before announcing the route to its connected CE
routers.
VPN-IPv4 addresses have the following format:
•
Route distinguisher is a 6-byte value that you can specify in one of the following formats:
•
as-number:number, where as-number is an AS number (a 2-byte value) and number
is any 4-byte value. The AS number can be in the range 1 through 65,535. We
recommend that you use an Internet Assigned Numbers Authority (IANA)-assigned,
Copyright © 2017, Juniper Networks, Inc.816
ACX Series Universal Access Router Configuration Guide
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