Cisco NCS 5500 Series Configuration Manual page 125

Implementing BGP
L3VPN Per-CE Mode
In this scenario, LOW-FIB scale line card is present in the core network and HIGH-FIB scale line card is
present in the customer facing network. This combination of the LOW-FIB and HIGH-FIB scale line cards
is used while operating in the per-CE VPN mode. In the per-CE mode, one label is assigned for every CE
next-hop from which BGP learns the VRF routes. The packet flow in this mode is as follows:
• Imposition (Ingress) PE: A VRF-IP lookup on the HIGH-FIB line card is performed. After the lookup,
the VPN label and transport label is pushed for disposition (egress) to the PE's loopback address. In the
core or the backbone network, a label switch is performed on the packet.
• Disposition (Egress) PE: The packet received from the core or the backbone network contains the
VPN-label.
In the per-CE mode, the VPN-label is assigned per CE. The VPN-label lookup on the core facing line
card (LOW-FIB scale line card) results in the next-hop to the HIGH-FIB line card, which is connected
to the CE.
BGP Configuration Guide for Cisco NCS 5500 Series Routers, IOS XR Release 6.2.x
Selective FIB Download
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