H3C Technologies H3C SR8800 - Manual (Page 254)

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Figure 72 Application of BGP AS number substitution
In Figure 72 , both CE 1 and CE 2 use the AS number of 800. AS number substitution is enabled on PE
2 for CE 2. Before advertising updates received from CE 1 to CE 2, PE 2 finds that an AS number in the
AS_PATH is the same as that of CE 2 and hence substitutes its own AS number 100 for the AS number.
In this way, CE 2 can normally receive the routing information from CE 1.
AS number substitution also applies to a PE connecting multiple CEs through different interfaces, such as
PE 2 in Figure 72 , which connects CE 2 and CE 3.
NOTE:
For a multi-homed CE, that is, a CE connected with multiple PEs, the BGP AS number substitution function
must be used in combination with the site-of-origin (SOO) function. Otherwise, routing loops may appear.
Multi-VPN-instance CE
Background
BGP/MPLS VPN transmits private network data through MPLS tunnels over the public network. However,
the traditional MPLS L3VPN architecture requires that each VPN instance exclusively use a CE to connect
with a PE, as shown in
Figure 55 .
For better services and higher security, a private network is usually divided into multiple VPNs to isolate
services. To meet these requirements, you can configure a CE for each VPN, which, apparently, will
increase users’ device expense and maintenance costs. Or, you can configure multiple VPNs to use the
same CE and the same routing table, which cannot ensure the data security.
Using the Multi-VPN-Instance CE (MCE) function, you can remove the contradiction of low cost and high
security in multi-VPN networks. MCE allows you to bind each VPN to a VLAN interface. The MCE creates
and maintains a separate routing table for each VPN. This separates the forwarding paths of packets of
different VPNs and, in conjunction with the PE, can correctly advertise the routes of each VPN to the peer
PE, ensuring the normal transmission of VPN packets over the public network.
How MCE works
The following uses Figure 73 to describe how an MCE maintains the routing entries for multiple VPNs and
exchanges VPN routes with PEs.