Restrictions for MPLS L3VPN
Implementing MPLS L3VPN in Cisco NCS 540 Series Routers is subjected to these restrictions:
• The Cisco NCS 540 Series router supports only 16 ECMP paths.
• Fragmentation of MPLS packets that exceed egress MTU is not supported. Fragmentation is not supported
for IP->MPLS imposition as well. Hence, it is recommended to use Maximum MTU (9216) value on all
interfaces in the MPLS core.
• L3VPN prefix lookup always yields a single path. In case of multiple paths at IGP or BGP level, path
selection at each level is done using the prefix hash in control plane. The selected path is programmed
in the data plane.
• TTL propagation cannot be disabled. TTL propagation always happens from IP->MPLS and MPLS->IP.
Apart from the specific ones mentioned above, these generic restrictions for implementing MPLS L3VPNs
also apply for Cisco NCS 540 Series Routers:
• Multihop VPN-IPv4 eBGP is not supported for configuring eBGP routing between autonomous systems
or subautonomous systems in an MPLS VPN.
• MPLS VPN supports only IPv4 address families.
The following platform restrictions apply only to Cisco NCS 540 Series router:
• MPLS-TE stats is not supported.
• MPLS stats is not supported on show mpls forwarding command output and does not show any MPLS
stats.
The following restrictions apply when configuring MPLS VPN Inter-AS with ASBRs exchanging IPv4 routes
and MPLS labels:
• For networks configured with eBGP multihop, a label switched path (LSP) must be configured between
non adjacent routers.
The physical interfaces that connect the BGP speakers must support FIB and MPLS.
Note
Inter-AS Support for L3VPN
This section contains the following topics:
Inter-AS Support: Overview
An autonomous system (AS) is a single network or group of networks that is controlled by a common system
administration group and uses a single, clearly defined routing protocol.
As VPNs grow, their requirements expand. In some cases, VPNs need to reside on different autonomous
systems in different geographic areas. In addition, some VPNs need to extend across multiple service providers
(overlapping VPNs). Regardless of the complexity and location of the VPNs, the connection between
autonomous systems must be seamless.
L3VPN Configuration Guide for Cisco NCS 540 Series Routers, IOS XR Release 6.3.x
3
MPLS L3VPN Overview
Restrictions for MPLS L3VPN
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