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Cisco 7600 Series Router Cisco IOS Software Configuration Guide, Release 12.2SX
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Chapter 24 Configuring PFC3BXL and PFC3B Mode Multiprotocol Label Switching
PFC3BXL or PFC3B Mode VPN Switching
PFC3BXL or PFC3B looks up the IP destination address in the CEF table but only against prefixes that
are in the specific VPN. (The table entry points to a specific set of adjacencies and one is chosen as part
of the load-balancing decision if multiple parallel paths exist.)
The table entry contains the information on the Layer 2 header that the packet needs, as well as the
specific MPLS labels to be pushed onto the frame. The information to rewrite the packet goes back to
the ingress line card where it is rewritten and forwarded to the egress line interface.
VPN traffic is handled at the egress from the PE based upon the per-prefix labels or aggregate labels. If
per-prefix labels are used, then each VPN prefix has a unique label association; this allows the PE to
forward the packet to the final destination based upon a label lookup in the FIB.
Note The PFC3BXL or PFC3B allocates only one aggregate label per VRF.
If aggregate labels are used for disposition in an egress PE, many prefixes on the multiple interfaces may
be associated with the label. In this case, the PFC3BXL or PFC3B must perform an IP lookup to
determine the final destination. The IP lookup may require recirculation.
MPLS VPN Guidelines and Restrictions
When configuring MPLS VPN, follow these guidelines and restrictions:
• PFC3BXL or PFC3B mode supports a total of 1024 VRFs per chassis a with enhanced OSMs; using
a nonenhanced OSM causes the system to default to 511 VRFs.
• In PFC3BXL or PFC3B mode, VPNs are recirculated when the number of VPNs is over 511.
PFC3BXL or PFC3B Mode MPLS VPN Supported Commands
PFC3BXL or PFC3B mode MPLS VPN supports these commands:
• address-family
• exit-address-family
• import map
• ip route vrf
• ip route forwarding
• ip vrf
• neighbor activate
• rd
• route-target
For information about these commands, see these publications:
http://www.cisco.com/en/US/docs/ios/12_2/switch/command/reference/fswtch_r.html
Configuring MPLS VPN
For information on configuring MPLS VPN, refer to the MPLS Virtual Private Networks feature module
at this URL:
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