Cisco Cisco IOS Software Release 12.0(13)S7
MPLS Safe Label Reuse After Router Restart
Information About MPLS Safe Label Reuse
3
Cisco IOS Release 12.0(32)SY
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When the router reloads, its persistent data file has a record of the labels in use before the restart. This
allows the MPLS label allocator to avoid labels in use before the restart until it is safe to reuse them.
allows the MPLS label allocator to avoid labels in use before the restart until it is safe to reuse them.
With the MPLS Safe Label Reuse feature, during normal operation, a router updates the persistent-data
file as required to represent its label usage to prepare for the next restart.
file as required to represent its label usage to prepare for the next restart.
The MPLS Safe Label Reuse feature is enabled by default in Cisco IOS Release 12.0(32)SY and later
releases. However, you can disable the feature and change some aspects of the feature. For information
on what aspects you can change, see the
releases. However, you can disable the feature and change some aspects of the feature. For information
on what aspects you can change, see the
.
Note
A switchover restart in MPLS SSO mode will not result in incorrect label reuse because MPLS SSO
saves local label bindings across SSO switchovers. However, a router configured in SSO mode might
leave SSO mode. While the router operates in non-SSO mode it is at risk for unsafe label reuse should
it restart unless the MPLS Safe Label Reuse feature is in use.
saves local label bindings across SSO switchovers. However, a router configured in SSO mode might
leave SSO mode. While the router operates in non-SSO mode it is at risk for unsafe label reuse should
it restart unless the MPLS Safe Label Reuse feature is in use.
Note
MPLS SSO is not supported in Cisco IOS Release 12.0(32)SY.
Persistent Data for MPLS Safe Label Reuse
The router saves and records information about MPLS label usage as persistent data or pdata in the
persistent-data file on the NVRAM device. Persistent data about MPLS labels is for groups of labels
called label blocks. The persistent data for a label block is called a pblock. The pblock represents the
usage state of the labels in the label block. The usage states for pblocks are:
persistent-data file on the NVRAM device. Persistent data about MPLS labels is for groups of labels
called label blocks. The persistent data for a label block is called a pblock. The pblock represents the
usage state of the labels in the label block. The usage states for pblocks are:
•
In-use—The labels represented by the label block are in use by the MPLS label allocator.
Immediately after a restart, the in-use blocks transition to the timing-out state.
Immediately after a restart, the in-use blocks transition to the timing-out state.
•
Free—Label blocks not in use by the MPLS label allocator and available should the label allocator
require more labels than available in the in-use label blocks. When the label allocator takes free label
blocks, the blocks transition to the in-use state.
require more labels than available in the in-use label blocks. When the label allocator takes free label
blocks, the blocks transition to the in-use state.
•
Timing-out—Label blocks that are not available for allocation until the safe-to-use timer expires.
When the timer expires, timing-out blocks transition to the free state.
When the timer expires, timing-out blocks transition to the free state.
Immediately following a restart, the router reads the state of the pblocks from the persistent-data file to
determine which pblocks, if any, are immediately available for use. The router confines label allocation
to pblocks not in use before the restart until the safe-to-use timer expires. If all pblocks are in the in-use
state when a restart occurs, no labels are available until the safe-to-use timer expires.
determine which pblocks, if any, are immediately available for use. The router confines label allocation
to pblocks not in use before the restart until the safe-to-use timer expires. If all pblocks are in the in-use
state when a restart occurs, no labels are available until the safe-to-use timer expires.
You might be running MPLS applications that require the use of most (or all) labels from the label space.
If this is the case, immediately after a restart most (or all) label pblocks would be in the timing-out state
and temporarily unavailable. The labels corresponding to these pblocks would not be available until the
safe-to-use timer expires.
If this is the case, immediately after a restart most (or all) label pblocks would be in the timing-out state
and temporarily unavailable. The labels corresponding to these pblocks would not be available until the
safe-to-use timer expires.