Controlling Route Importation

You can control how many routes a PE router can add to a particular VRF’s forwarding table by specifying a maximum limit and a warning threshold. When the router attempts to add a route, it compares the limit you configure against a route count it maintains for routes already in the VRF’s forwarding table.

With a warning threshold configured, the following behavior takes place when the PE router attempts to add a route:

• When adding the route causes the route count to exceed the warning threshold for the first time, the router adds the route and generates a warning-threshold-exceeded log entry.
• As long as the route count stays above the warning threshold, adding more routes does not generate more warning-threshold-exceeded log entries.
• If the route count fluctuates below and above the warning threshold due to route deletions and additions, an interval of 5 minutes since the last warning-threshold-exceeded log entry must pass before another warning-threshold-exceeded log entry can be generated. This behavior prevents the system log from being flooded with log entries.

With a limit configured, the following behavior takes place when the PE router attempts to add a route:

• When adding the route causes the route count to exceed the limit for the first time, the router rejects the route and generates a limit-exceeded log entry.
• As long as the route count stays at the limit, further attempts to add routes fail, but do not generate any more limit-exceeded log entries.
• If the route count fluctuates below and up to the limit due to route deletions and additions, no further limit-exceeded log entries are generated until a 5-minute interval has passed since the last limit-exceeded log entry. This behavior prevents the system log from being flooded with log entries.

When you issue the command, the router immediately reevaluates the current number of routes against the new limit. If the current number of routes is greater than the maximum configured limit, the router might remove dynamically learned routes in order to enforce the new limit.

maximum routes

• Use to prevent a PE router from importing too many routes from attached CE routers into a particular VRF.
• When the router attempts to add a route that exceeds the warningThreshold, the router generates a warning-threshold log entry and adds the route. An interval of 5 minutes must pass before another warning-threshold-exceeded message can be generated.
• When the router attempts to add a route that exceeds the limit, the router generates a limit-exceeded warning and rejects the route. An interval of 5 minutes must pass before another limit-exceeded message can be generated.
• Messages are logged to ipRouteTable at severity warning.
• The interval timers for the limit and the warning threshold are independent.
• You can use the warning-only keyword to specify that the router add the route and generate a warning-threshold-exceeded log entry (instead of a limit-exceeded log entry) when the limit is exceeded.
• Issuing the command causes the router to evaluate the current route count and determine whether to generate new messages; any existing warning threshold or limit timers are reset to zero.
• Example

  host1(config-vrf)#maximum routes 80 65

• Use the no version to remove the limit and warning threshold.
• See maximum routes.

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