For example, in a BGP/MPLS VPN topology, LDP or RSVP-TE adds routes to the tunnel
routing table for all available tunnels. BGP performs a lookup in the tunnel routing
table so that it can resolve indirect next hops.
You can clear the routes from the tunnel routing table. You might do this, for example,
to reapply routing policies when the policies are changed.
Related Topics â– MPLS Forwarding and Next-Hop Tables on page 224
â– Clearing and Refreshing IPv4 Dynamic Routes in the Tunnel Routing Table
â– Clearing and Refreshing IPv6 Dynamic Routes in the Tunnel Routing Table
â– Explicit Routing for MPLS on page 226
Explicit Routing for MPLS
MPLS offers two options for selecting routing paths:
â– Hop-by-hop routing
â– Explicit routing
In explicit routing, the route the LSP takes is defined by the ingress node. The path
consists of a series of hops defined by the ingress LSR. Each hop can be a traditional
interface, an autonomous system, or an LSP. A hop can be strict or loose.
A strict hop must be directly connected (that is, adjacent) to the previous node in the
path. A loose hop is not necessarily directly connected to the previous node; whether
it is directly connected is unknown.
The sequence of hops comprising an explicit routing LSP may be chosen in either of
the following ways:
â– Through a user-defined configuration, resulting in configured explicit paths. When
you create the explicit route, you must manually configure each hop in the path.
■Through a routing protocol–defined configuration, resulting in dynamic explicit
paths. When the routing protocol (IS-IS or OSPF) creates the explicit path, it
makes use of the topological information learned from a link-state database in
order to compute the entire path, beginning at the ingress node and ending at
the egress node.
Consider the MPLS domain shown in Figure 55 on page 227. Without explicit path
routing, the tunnel is created hop by hop along the following path:
LSR 1 –> LSR 3 –> LSR 4 –> LSR 7
Suppose LSR 5 and LSR 6 are underused and LSR 4 is overused. In this case you
might choose to configure the following explicit path because it forwards the data
better than the hop-by-hop path:
LSR 1 –> LSR 3 –> LSR 5 –> LSR 6 –> LSR 7
226 â– Explicit Routing for MPLS
JUNOSe 11.1.x BGP and MPLS Configuration Guide
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