PFR/OER question

[CARLO CIANFARANI]

Hi,

reading CCO documentation for OER it is not so clear to me the difference between backoff timer (3 values used for dampening) anf holddown timer

BTW which are the triggers for OER to evaluate the MTCs and in turn move them to another exit link (if that is the case...)

thanks for your help !

[CARLO CIANFARANI]

Any idea ?

thanks.

[Giuseppe Larosa]

Hello Carlo,

from PFR configuration guide for 15.0M the following definitions of the timers are provided:

PfR Timers Parameters

Three types of timers can be configured as PfR policy operational parameters:

Backoff Timer

The backoff timer is used to adjust the transition period that the master controller holds an out-of-policy

traffic class entry. The master controller waits for the transition period before making an attempt to find an

in-policy exit. A minimum, a maximum, and an optional step timer value can be configured.

Holddown Timer

The holddown timer is used to configure the traffic class entry route dampening timer to set the minimum

period of time that a new exit must be used before an alternate exit can be selected. To prevent the traffic

class entry from flapping because of rapid state changes, the master controller does not move the traffic

class entry to a different exit even if it goes out-of-policy during the holddown timer period. PfR does not

implement policy changes while a traffic class entry is in the holddown state. A traffic class entry will

remain in a holddown state for the default or configured time period. When the holddown timer expires,

PfR will select the best exit based on performance and policy configuration. However, an immediate route

change will be triggered if the current exit for a traffic class entry becomes unreachable.

Periodic Timer

The periodic timer is used to find a better path for a traffic class entry, even if the traffic class entry is inpolicy

on the current exit. When the periodic timer expires, the master controller evaluates current exit

links for the traffic class entry and, if a better exit exists based on the current measurements and priorities,

the traffic class entry is moved to a new in-policy exit link.

When adjusting PfR timers note that a newly configured timer setting will immediately replace the existing

setting if the value of the new setting is less than the time remaining. If the value is greater than the time

remaining, the new setting will be applied when the existing timer expires or is reset.

Hope to help

Giuseppe

[CARLO CIANFARANI]

Thanks for the reply....

Let me ask about some point:

- backoff timer: consider a traffic class (TC) that at a point in time goes out-of-policy and currently exist another in-policy exit: does PFR moves the TC to the available in-policy exit or, anyway, moves it into OOP state until backoff timer expire ?

- Periodic timer: from configuration guide it seem to me it make sense only if mode select-exit best is operation (in other words: if in mode select-exit good upon timer expires PFR basically does nothing.. )

thanks in advance