Traffic Forwarding
Directing Traffic to an MPLS TE Tunnel
- Static Route: applies to networks with simple or stable network topologies.
- PBR: applies to load balancing and security monitoring scenarios.
- Tunnel Policy: applies to scenarios where TE VPN services are transmitted over TE tunnels.
- Auto Route: applies to networks with complex or variable network topologies.
Static Route
The simplest method to direct traffic to an MPLS TE tunnel is to configure a static route and specify a TE tunnel interface as the outbound interface.
PBR
Policy-based routing (PBR) allows for route selection based on user-defined policies, and is applicable to security-sensitive or load balancing scenarios. On a PBR-capable MPLS network, IP packets are forwarded over specific CR-LSPs based on PBR rules.
MPLS TE PBR is implemented based on a set of matching rules and behaviors. The rules and behaviors are defined using apply clauses, in which the outbound interface is a specific tunnel interface. If packets do not match any PBR rules, they are forwarded following the IP routing process. If they match PBR rules, they are forwarded over specific CR-LSPs.
Tunnel Policy
- Select-seq policy: selects a TE tunnel to transmit VPN traffic on the public network by configuring an appropriate tunnel selection sequence.
- Tunnel binding policy: binds a TE tunnel to a destination address to provide QoS guarantee.
Auto Route
The auto route feature allows a TE tunnel to participate in IGP route calculations as a logical link. The tunnel interface is used as the outbound interface of the route. The tunnel is considered a point-to-point (P2P) link with a specified metric. Two auto route types are available:
IGP shortcut: An LSP tunnel is not advertised to neighbor nodes, so it will not be used by other nodes.
Forwarding adjacency: An LSP tunnel is advertised to neighboring nodes, so it can be used by these nodes.
Forwarding adjacency advertises LSP tunnels by carrying neighbor IP address in the Remote IP Address sub-TLV of OSPF Type-10 Opaque LSAs or the Remote IP Address sub-TLV of IS Reachability TLV.
To use the forwarding adjacency feature, nodes on both ends of a tunnel must be located in the same area.
The following example shows the differences between IGP shortcut and forwarding adjacency.
- If auto route is not configured, Router_5 uses Router_4 as the next hop, and Router_7 uses Router_6 as the next hop.
- If auto route is used:
When Tunnel0/0/1 is advertised using IGP shortcut, Router_5 uses Router_4 as the next hop, and Router_7 uses Tunnel0/0/1 as the next hop. Because Tunnel0/0/1 is not advertised to Router_5, only Router_7 selects Tunnel0/0/1 using the IGP.
When Tunnel0/0/1 is advertised using forwarding adjacency, Router_5 uses Router_7 as the next hop, and Router_7 uses Tunnel0/0/1 as the next hop. Because Tunnel0/0/1 is advertised to Router_5 and Router_7, both the two nodes select Tunnel0/0/1 using the IGP.