Cisco Cisco IOS Software Release 12.2(33)SRE

As shown in 

, a fast reroutable TE LSP with a backup tunnel exists from Router1 to Router 2 to 

Router 3.

This TE LSP has a backup tunnel from Router 1 to Router 3 protecting the fast reroutable TE LSP against 
a failure in the Router 1-Router 2 link and node Router 2. However, assume that a failure occurs in the 
link connecting Router 1 to Router 2. 

If hellos were running between Router 1 and Router 2, they would notice that the link is down, but would 
not time out the state. Router 2 notices the failure, but cannot time out the TE LSP because Router 2 may 
be a merge point or another downstream node may be a merge point. Router 1 notices the failure and 
switches to the backup LSP; however, Router 1 cannot time out the state either. 

A hello instance is not created in the preceding scenario because the neighbor is down and the hello 
instance cannot take action.

As shown in 

, a fast-reroutable TE LSP without a backup tunnel exists from Router 1, the point 

of local repair (PLR), to Router 2 to Router 3. 

Assume that a failure occurs in the link connecting Router 1 to Router 3. Router 1 can time out the state 
for the TE LSP because Router 1 knows there is no backup tunnel. However, Router 2 cannot time out 
the state because Router 2 does not know whether a backup tunnel exists. Also, Router 2 may be a merge 
point, and therefore, cannot time out the state.

A hello instance is not created in the preceding scenario because the neighbor is down and the hello 
instance cannot take action.

117935

Router 1

Router 3

Router 2

Merge Point

Backup Tunnel

117936

Router 1

PLR

Router 3

Router 2

Merge Point