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Implementing MPLS VPNs over IP Tunnels on Cisco IOS XR Software
Information About MPLS VPNs over IP Tunnels
MPC-276
Cisco IOS XR MPLS Configuration Guide
OL-12284-01
Packet Validation Mechanism
The MPLS VPNs over IP Tunnels feature provides a simple mechanism to validate received packets
from appropriate peers. The multipoint L2TPv3 tunnel header is automatically configured with a 64-bit
cookie and L2TPv3 session ID. This packet validation mechanism protects the VPN from illegitimate
traffic sources. The cookie and session ID are not user-configurable, but they are visible in the packet as
it is routed between the two tunnel endpoints. Note that this packet validation mechanism does not
protect the VPN from hackers who are able to monitor legitimate traffic between PE routers.
Quality of Service Using the Modular QoS CLI
To configure the bandwidth on the encapsulation and decapsulation interfaces, use the modular QoS CLI
(MQC).
Note This task is optional.
Use the MQC to configure the IP precedence or Differentiated Services Code Point (DSCP) value set in
the IP carrier header during packet encapsulation. To set these values, enter a standalone set command
or a police command using the keyword tunnel. In the input policy on the encapsulation interface, you
can set the precedence or DSCP value in the IP payload header by using MQC commands without the
keyword tunnel.
Note You must attach a QoS policy to the physical interface—not to the tunnel interface.
If Modified Deficit Round Robin (MDRR)/Weighted Random Early Detection (WRED) is configured
for the encapsulation interface in the input direction, the final value of the precedence or DSCP field in
the IP carrier header is used to determine the precedence class for which the MDRR/WRED policy is
applied. On the decapsulation interface in the input direction, you can configure a QoS policy based on
the precedence or DSCP value in the IP carrier header of the received packet. In this case, an MQC policy
with a class to match on precedence or DSCP value will match the precedence or DSCP value in the
received IP carrier header. Similarly, the precedence class for which the MDRR/WRED policy is applied
on the decapsulation input direction is also determined by precedence or DSCP value in the IP carrier
header.
BGP Multipath Load Sharing for MPLS VPNs over IP Tunnels
BGP Multipath Load Sharing for EBGP and IBGP lets you configure multipath load balancing with both
external BGP and internal BGP paths in BGP networks that are configured to use MPLS VPNs. (When
faced with multiple routes to the same destination, BGP chooses the best route for routing traffic toward
the destination so that no individual router is overburdened.)
BGP Multipath Load Sharing is useful for multihomed autonomous systems and PE routers that import
both EBGP and IBGP paths from multihomed and stub networks.