13-6
Cisco SCE 2000 and SCE 1000 Software Configuration Guide
OL-7827-12
Chapter 13 MPLS/VPN Support
Service Control MPLS/VPN Concepts
BGP LEG Tasks in the MPLS/VPN Solution
• The BGP LEG is a software module that runs on the SM server
• The LEG maintains a BGP session with a list of PEs
• After the sessions establishment, the LEG propagates MP-BGP route-updates from the PEs to the
SM module
SM Tasks in the MPLS/VPN Solution
• The VPNs are stored in the SM database.
• Each VPN is defined by:
–
The IP address of the loopback interface of the PE router.
–
The RD or RT that identifies the VPN within the PE router.
• A VPN-based subscriber is defined by the IP range in a specified VPN or the BGP community (CE
as subscriber).
• The SM receives updates from the BGP LEG, and updates the VPN information with the new MPLS
labels.
• The relevant SCE platforms that will get the MPLS updates are defined by the VPN domain.
Service Control MPLS/VPN Concepts
• Non-VPN-Based Subscribers, page 13-6
• Bypassing Unknown VPNs, page 13-7
• Additional MPLS Pattern Support, page 13-7
• VPN Identifier (RD or RT), page 13-8
Non-VPN-Based Subscribers
The MPLS/VPN solution supports the existence of non-VPN-based (regular IP) subscribers concurrently
with the MPLS/VPN-based subscribers, with the following limitations and requirements:
• The SM must work in "push" mode.
• Non-VPN-based subscribers cannot have IP in VPN mappings.
• VLAN-based subscribers are NOT supported at the same time as MPLS/VPN-based subscribers.
In typical MPLS/VPN networks, traffic that does not belong to any VPN is labeled with a single MPLS
label in the upstream direction, which is used for routing. The downstream direction of such flows
typically contains no label, due to penultimate hop popping.
The SCE platform uses the one or more labels upstream and no label downstream definition to identify
non-VPN flows. Classification and traffic processor load balancing on these flows is performed
according to the IP header, rather than the label.
This process requires learning of the upstream labels in use for such flows, and is done using the flow
detection mechanism described above (see Flow Detection, page 13-3).
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