Riverstone Networks WICT1-12 - Manual (Page 344)

17-36 Riverstone Networks RS Switch Router User Guide Release 8.0
Configuring L3 Label Switched Paths MPLS Configuration
If you are using IGP shortcuts, the LSP metric value can be added to other IGP metrics to determine the total cost of
the path. IGP path and LSP metric values can be compared to determine the preferred path. For more information about
using LSPs as IGP shortcuts, see
Section 17.7.3, "IGP Shortcuts."
If an LSP exists between two BGP peers, the LSP metric represents to downstream BGP neighbors a cost value that
does not change even if the LSP is rerouted.
Disabling CSPF
The
no-cspf
parameter disables constrained path LSP computations by the ingress LSR and must be specified when
configuring an explicit path LSP. This parameter must not be specified with constrained shortest path first (CSPF)
configurations; for an explanation of CSPF and configuration examples, see
Section 17.7, "Traffic Engineering."
Disabling TTL Decrementing
With normal decrementing, the (time-to-live) TTL field in an IP packet header is decremented by 1 on each LSR in
the LSP. With the
no-decrement-ttl
parameter, the IP packet's TTL field is only decremented by 1 at the egress
router when the entire LSP is traversed, thus making the whole LSP appear as one hop. The
no-decrement-ttl
parameter can be applied to RSVP-signaled LSPs only. Note that the MPLS label has its own TTL that is decremented
by 1 for each hop in the LSP. When the label is popped at the PHP router, the label's TTL value is not written to the
IP packet's TTL and the IP packet's TTL is decremented by 1 at the egress LSR.
Disabling Path Route Recording
By default, RSVP-signaled LSPs on RS routers record path route information. While this information may be useful
for troubleshooting, this function must be supported on all transit routers. Specify the
no-record-route
option to
disable the recording.
Preference
The default preference value for an LSP is 7, which, with the exception of direct routes, is more preferred than all
learned routes. Where there are multiple LSPs between the same source and destination, you can assign a different
preference value to an LSP. A smaller value signifies a more desirable path.
Connection Retries
The ingress LSR tries to connect to the egress router over the primary path at 15-second intervals for up to 5000
attempts. You can change the intervals at which connections are attempted with the
retry-interval
parameter or
change the maximum number of attempts with the
retry-limit
parameter. If the number of attempts by the ingress
LSR to connect to the egress router exceeds the
retry-limit
parameter, you will need to restart the primary path.