Figure 24: Sample Service Path Preference scenario
The ingress PE (PE1) receives the routes from the customers. The local policies determine the attribute to be
assigned to the customer. PE1 associates a forward-class to the prefix based on the local policies that are
created based on the VFI or EVI service. The pre-configured tunnel with matching forward-class is selected
for forwarding the traffic.
L2VPN Route Policy
L2VPN route-policy feature enables the export community configuration for L2VPN VPWS and L2VPN
VPLS with BGP autodiscovery. BGP executes the route-policy. This functionality is similar to the route-policy
support under BGP submode for L3VPN services.
The following points explain the L2VPN route-policy functionality:
1. The RPL is used to set standard community as policy action for two new attachpoints that are L2VPN
export VPLS (VFI) and L2VPN export VPWS (MP2MP).
2. L2VPN configuration specifies which route-policy to use for a given bridge-domain configured with BGP
autodiscovery.
3. L2VPN sends the route-policy name to BGP along with the L2VPN context.
4. BGP process inserts standard community to the L2 NLRI.
Interoperability Between Cisco IOS XR and Cisco IOS on VPLS LDP Signaling
The Cisco IOS Software encodes the NLRI length in the fist byte in bits format in the BGP Update message.
However, the Cisco IOS XR Software interprets the NLRI length in 2 bytes. Therefore, when the BGP neighbor
with VPLS-VPWS address family is configured between the IOS and the IOS XR, NLRI mismatch can happen,
leading to flapping between neighbors. To avoid this conflict, IOS supports prefix-length-size 2 command
that needs to be enabled for IOS to work with IOS XR. When the prefix-length-size 2 command is configured
in IOS, the NLRI length is encoded in bytes. This configuration is mandatory for IOS to work with IOS XR.
This is a sample IOS configuration with the prefix-length-size 2 command:
L2VPN and Ethernet Services Configuration Guide for Cisco ASR 9000 Series Routers, IOS XR Release 6.3.x
212
Implementing Multipoint Layer 2 Services
L2VPN Route Policy
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