I believe that section 8.3.2 - "Recommendations Regarding Setting Priority Values" is incorrect.
1. Second paragraph, "especially if preemption is set" should be deleted. Only one Virtual Router can be the address owner, and the "especially ..." implies that there are circumstances under which more than one Virtual Router can be configured with priority 255. 2. Third paragraph. This paragraph states that uniformly distributing priority values "facilitates faster convergence". This is not correct; using higher priorities results in faster convergence, since the higher the priority the lower the value of Skew_Time, and hence Active_Down_Interval. In order to achieve the fastest transition of a Backup Router to Active Router after the original Active Router fails or shuts down, the priorities should be configured to be as high as possible. This needs to be tempered by the differences in Skew_Time between the various Backup Routers should be sufficiently large that the second highest priority Backup Router consistently does not transition to be an Active Router since it sees the first advertisement from what was the highest priority Backup Router before Active_Down_Interval expires on the second (and lower) priority Backup Routers. I believe the following could replace the third paragraph: "For the fastest transition of a Backup Router to Active Router after the original Active Router fails or is shut down, configured priorities should be as high as possible, since this reduces Skew_Time. It is important that the differences in Skew_Time between the Virtual Routers are sufficiently large that the highest priority Backup Router transitions to Active Router and sends an advert before Active_Down_Interval expires on any other any Backup Router, thereby ensuring that only one Backup Router transitions to be an Active Router. It should be noted that this is more critical with lower Advertisement_Intervals, and priorities that work with an Advertisement_Interval of, for example, 100 may not work reliably with an Advertisement_Interval of, for example, 10." Equal priority Virtual Routers ============================== Whilst the VRRP protocol and procedures work with Backup Routers having equal priorities, it causes operational problems due to two, or more, Backup Routers transitioning to Active state simultaneously, and learning bridges updating their MAC address caches following the failure or shutdown of the previous Active Router. This will only be corrected once the Virtual Router with the higher primary IPvX address next sends an advert (I have separately proposed that if an Active Router receives an advert from a lower priority (or equal priority and lower IPvX primary address) Virtual Router, it should immediately send an advertisement rather than wait for Adver_Timer to expire, thereby speeding up the recovery from having two (or more) Active Routers). I therefore suggest adding the following paragraph at the end of section 8.3.2: "In order to avoid two or more Backup Routers simultaneously becoming Active Routers after the previous Active Router fails or is shut down, all Virtual Routers SHOULD be configured with different priorities, and with sufficient differences in priority so that lower priority Backup Routers do not transition to Active state before receiving an advertisement from the highest priority Backup Router following it transitioning to Active Router." With regards, Quentin Armitage _______________________________________________ rtgwg mailing list [email protected] https://www.ietf.org/mailman/listinfo/rtgwg
