Hello all, I'm sure most, if not all of you are familiar with the filters that various ISP's and NSP's have placed on received BGP announcements. Most famous for this is/was? SprintLinks filter policy, which is documented at http://www.sprintlink.net/filter.htm Recently the subject of announcement filters and route-dampening policy has become increasing relevant to a number of my customers, especially when making sound architecture decisions. Unfortunately, few providers have documented their filter policies (to my knowledge) as well as SprintLink. I'm not even sure Sprint follows the policy anymore. I have specific knowledge of several cases where they are listening to /24's announced by some companies (albeit these are very high profile, and would easily be justified as exceptions to the rule) My question to you, and I believe NANOG to be the most appropriate forum I know of in this regard, is the perenial "what is the current general policy" in this regard. I can think of a few ways to get limitted knowledge about providers policies by checking for received-announcements on edge routers/looking glasses which receive transit from other providers (e.g. go to an MCI customer and look for short prefix announcements known to be announced at, say, Mae-East). Unfortunately, this is not particularly sound, and is high-effort. Further, it does nothing to address the second question of mine, which is what the current typical route-dampening policies are. Third, and this isn't North-American related, so please refer me to better sources, should they exist, are these policies any different for other geographic areas? (e.g. will people listen to smaller announcements at international peering points, do people place different filters for APNIC address space, etc.) Finally, what is the typical reconvergence time for BGP in the global Internet today? For full disclosure, my company makes high availability and load balancing products, and I would certainly prefer these questions be answered in certain ways. I am, however, most interested in the truth so I can give educated advice to my customers. It seems like it is no longer reasonable to keep constant track of who is doing what with routing policies, as it isn't a simple matter of keeping state on 4-8 providers. At least not unless driving BGP sessions is your day-to-day job. Currently, my best answers (qualified with "I may be out of date" are (1) Varies, but a /19 is probably safe, any smaller likely depends on who you buy transit from. (2) Default dampening settings. (3) I don't remember, several ideas were kicked around. (4) 15-20 minutes, depending on lots of variables. Thanks for everyones input on this, any pointers are greatly appreciated. --D -- -- Darren Bolding darren@f5.com -- -- Principal Consultant --