RIPE-229 RIPE Routing-WG Recommendations for Coordinated Route-flap Damping Parameters - Errors/Mistakes?
Zvezdelin Vladov zvladov at mobikom.com
Tue Apr 27 09:40:08 CEST 2004
Dear All, I would like to point to you a major mistake throughout this recomendation that might lead to unexpected results, if exactly following the proposed parameters in the RIPE-229. Here they are: 1. At A3.1.1 it is said: "A.3.1.1 For /24s Parameters used are "set dampening 15 820 3000 30" 1st flap 1000 decay to 966, 982 at update 2nd flap 1966 decay to 1894, 1926 at update 3rd flap 2894 decay to 2787, 2846 at update 4th flap 3280 decay to 3165, 3226 at update" Although the comment futher states: "Maximum possible penalty is 3280 as defined by the flap parameters, so the penalty at the 4th flap was only incremented from 2787 to 3280, not 3787 as might have been expected. At the 4th flap the prefix was marked as being suppressed for 59 minutes when the update message was received. If the update after the 4th flap was not received within 4 minutes and 20 seconds, the penalty dropped below 3000, and the prefix was not suppressed." Please note the first line after the A.3.1.1, it is said: "set dampening 15 820 3000 30" And actually it is spoken of dampening parameters such as: "set dampening 30 820 3000 60" Please note the "59 minutes" on the 4th row from the last comment, counting from above to the bootom of the paragpraph. Configuring "15 820 3000 30" gives max penalty 3280, max suppresion time 30 minutes, instead of 60, which is in contradiction with the recomendations made at section 2. of the document. 2.2 Description of recommended damping parameter: Basically the recommended values do the following with harsher treatment for /24 and longer prefixes: * don't start damping until the 4th flap * /24 and longer prefixes: max=min outage 60 minutes 2. On the example configs actually given at http://www.golden-networks.net for the Cisco IOS config, the parameters for /24 are: "set dampening 30 820 3000 60", i.e. the correct values are in the config. So, I suggest correcting this document. One more suggestion is to note the standard dampening parameters for Cisco and Juniper, and especially the different penalty assigment policy - Cisco - on withdraw only, Juniper on withdraw AND readvertisement. Zvezdelin Vladov -- Zvezdelin Vladov Admin IP Network & Security Mobikom RTC Sofia Bulgaria AS8795 Ph:+359 2 9743804