Objectives
The simulator ticks each one as soon as the network meets it.
On PE1 create explicit path TOP with strict next-addresses 10.0.12.2 (P1) and 10.0.25.2 (PE2).
Build tunnel-te1 to 5.5.5.5 for 100000 kbps with autoroute announce, path-option 1 explicit name TOP and path-option 2 dynamic.
Check show mpls traffic-eng tunnels: path option 1 is refused for bandwidth, so the tunnel is up on path option 2 through P2 and P3.
Raise the RSVP bandwidth to 1000000 kbps on the top path: PE1 GigabitEthernet0/0/0/0, both P1 interfaces and PE2 GigabitEthernet0/0/0/0.
tunnel-te1 re-optimises onto path option 1 through P1.
Ping 5.5.5.5 from PE1 through the tunnel.
Before you start
Path options are tried in order, lowest number first; the first one that CSPF and RSVP accept carries the tunnel. A strict hop must be directly connected to the previous hop, and every link on the path must still have the requested bandwidth. When a better (lower-numbered) path option becomes possible, the head end re-optimises onto it.
Concept
Explicit paths and path options
A tunnel lists path options in order. A dynamic option lets CSPF choose; an explicit option names the hops the tunnel must take. Strict hops must be directly connected to the previous hop; loose hops can be reached over any TE path. The first option that can be signalled carries the tunnel.
Concept
CSPF: the shortest path that meets the constraints
An IGP always takes the lowest-cost path. MPLS traffic engineering lets the head end choose a different one: IS-IS floods every TE link with its TE metric and reservable bandwidth, and CSPF (constrained shortest path first) runs Dijkstra only over the links that meet the tunnel’s constraints.
