Configuring Route Exchange Between PE device and CE Devices

Context

The Hub-PE and Hub-CE devices can use IGP or EBGP to exchange routing information. When they use EBGP, you must configure the Hub-PE device to allow repeated local AS number.

As shown in Figure 1, the routing information advertised by a Spoke-CE is forwarded to the Hub-CE and Hub-PE device before being transmitted to other Spoke-PE devices. If EBGP runs between the Hub-PE device and the Hub-CE, the Hub-PE device performs the AS-Loop detection on the route. If the Hub-PE device detects its own AS number in the route, it discards the route. In this case, to implement the Hub and Spoke networking, the Hub-PE device must be configured to permit the existence of repeated local AS numbers.

Figure 1 EBGP running between the Hub-CE and Hub-PE devices

Procedure

Configure EBGP between the Hub-PE and Hub-CE devices.
For detailed configuration procedures, see Configuring a Routing Protocol Between PE device and CE.

The Spoke-PE and Spoke-CE devices can use EBGP, IGP, or static routes.

To set up an EBGP peer relationship between the Hub-PE and Hub-CE devices and between a Spoke-PE device and a Spoke-CE device, perform the following steps on the Hub-PE device:
1. Run system-view
  The system view is displayed.
2. Run bgp { as-number-plain | as-number-dot }
  The BGP view is displayed.
3. Run ipv4-family vpn-instance vpn-instance-name
  The BGP-VPN instance IPv4 address family view is displayed.
4. Run peer { group-name | ipv4-address } allow-as-loop [ number ] [ global-as [ vpn-as ] ]
  The Hub-PE is configured to allow the routing loop. Here the value of number is set as 1, which means the route with the AS repeated once can be sent.
Configure an IGP between the Hub-PE and Hub-CE devices.
For detailed configuration procedures, see Configuring a Routing Protocol Between PE and CE.

Only IGP or static routes can be used between the Spoke-PE and Spoke-CE devices. BGP can cause route flapping between them. If BGP is used, the source BGP route's AS number will get lost when the route is transmitted through the IGP running between the Hub-PE and Hub-CE. The Spoke-PE will receive both the source BGP route sent by the Spoke-CE and the source BGP route with no AS number forwarded by the Hub-PE. The source BGP route sent by the Spoke-CE has an AS number and is therefore not preferred by the Spoke-PE. After the route is withdrawn, the Spoke-PE prefers the source BGP route received from the Spoke-CE again and advertises this route again. As this process repeats, route flapping occurs.
Configure static routes between the Hub-PE and the Hub-CE devices.
For detailed configuration procedures, see Configuring a Routing Protocol Between PE device and CE.

EBGP, IGP, or static routes can be used between the Spoke-PE and the Spoke-CE devices.

If the Hub-CE device uses the default route to access the Hub-PE device, perform the following steps on the Hub-PE device to advertise the default route to all the Spoke-PE devices:
1. Run system-view
  The system view is displayed.
2. Run ip route-static vpn-instance vpn-source-name 0.0.0.0 0.0.0.0 nexthop-address [ preference preference | tag tag ]^* [ description text ]
  Here, vpn-instance-name refers to the VPN-out. nexthop-address is the IP address of the Hub-CE interface that is connected with the PE device interface bound with the VPN-out instance.
3. Run bgp { as-number-plain | as-number-dot }
  The BGP view is displayed.
4. Run ipv4-family vpn-instance vpn-instance-name
  The BGP-VPN instance IPv4 address family view is displayed. vpn-instance-name refers to the VPN-out instance.
5. Run network 0.0.0.0 0
  The default route is advertised to all the Spoke-PE devices through MP-BGP.