Implementing MPLS VPNs over IP Tunnels on Cisco IOS XR Software
Information About MPLS VPNs over IP Tunnels
Figure 24 Basic MPLS VPN over IP Topology
IPv4 | |||
1.1.1.1 | 3.3.3.3 | ||
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| Network |
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| (w/ ISIS) |
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V4: 100.1.10.0/24 |
| V4: 200.1.10.0/24 | |
V6: 100.1.10.0/64 |
| V6: 200.1.10.0/64 |
Prefix Advertised |
| Prefix Advertised |
V4: 110.0.0.1/18 | V4: 210.0.0.1/18 | |
V6: 110::1/120 | V6: 210::1/120 | |
210625
Advertising Tunnel Type and Tunnel Capabilities Between PE
Border Gateway Protocol (BGP) is used to advertise the tunnel endpoints and the subaddress family identifier (SAFI) specific attributes (which contains the tunnel type, and tunnel capabilities). This feature introduces the tunnel SAFI and the BGP
These attributes allow BGP to distribute tunnel encapsulation information between PE routers. VPNv4 traffic is routed through these tunnels. The next hop, advertised in BGP VPNv4 updates, determines which tunnel to use for routing tunnel traffic.
SAFI
The tunnel SAFI defines the tunnel endpoint and carries the endpoint IPv4 address and next hop. It is identified by the SAFI number 64.
BGP SSA
The BGP SSA carries the BGP preference and BGP flags. It also carries the tunnel cookie, tunnel cookie length, and session ID. It is identified by attribute number 19.
PE Routers and Address Space
One multipoint L2TPv3 tunnel must be configured on each PE router. To create the VPN, you must configure a unique Virtual Routing and Forwarding (VRF) instance. The tunnel that transports the VPN traffic across the core network resides in its own address space. A special purpose VRF called a Resolve in VRF (RiV) is created to manage the tunnel address space. You also configure the address space under the RiV that is associated with the tunnel and a static route in the RiV to route outgoing traffic through the tunnel.
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| Cisco IOS XR MPLS Configuration Guide |
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