Mpls L3Vpn Working Principles - Zte ZXR10 8900 Series User Manual

ZXR10 8900 Series User Manual (MPLS Volume)
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If the value of the type field is 1, the administrator subfield con-
tains an AS number. RFC2547bis recommends that the public
AS number for IANA allocation should be the AS number of the
ISP or the customer.
� Assignment number subfield
It is a number assigned by the ISPs.
If the type field is 0, the length of the Assignment number
subfield is two bytes.
If the type field is 1, the length of the Assignment number
subfield is four bytes.
An RD is only used between PEs to differentiate IPv4 addresses
of different VPNs. The ingress generates an RD and converts the
received IPv4 route of the CE into a VPN-IPv4 address. Before
advertising the route to the CE, the egress PE converts the VPN-
IPv4 route into an IPv4 route.

MPLS L3VPN Working Principles

Basic operation mode of MPLS VPN is the application of L3 tech-
nologies. Each VPN has an independent VPN-ID, users of each VPN
can only communicate with members in the same VPN and only
VPN members can enter VPN.
On MPLS-based VPNs, service provider assigns a distinguisher to
each VPN, called Route Distinguisher (RD). Distinguisher is unique
in network of service provider.
Forwarding table contains a unique address, called VPN-IP ad-
dress, which is formed through connection of the RD and IP ad-
dress of the user. VPN-IP address is a unique one in network.
Address table is stored in forwarding table.
BGP is a routing information distribution protocol, which uses
multi-protocol extension and common attributes to define VPN
connectivity. On MPLS-based VPNs, BGP only advertise informa-
tion to members in the same VPN and provide basic security by
means of traffic split.
Data is forwarded by using LSP. LSP defines a special path that
cannot be changed, to guarantee the security. Such a label-based
mode can provide confidentiality as frame relay and ATM. Service
provider relates a special VPN to an interface, and packet forward-
ing depends upon ingress labels.
VPN forwarding table contains a label corresponding to the VPN-IP
address. Label is used to send data to the corresponding destina-
tion. As label is used instead of IP address, a user can maintain
its dedicated address structure, without the need of data transfer
by means of Network Address Translation (NAT). According to data
ingress, corresponding router will select a special VPN forwarding
table that only contains a valid destination address in VPN.
First, CE provides routing information of client in net to PE router
by static routing, default routing or protocols like RIP, OSPF, IS-IS
or BGP.