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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Re: splitting up a /20 (was: Class B Address)
Also sprach William Allen Simpson >Matt Cramer wrote: >> My company has a /20 out of the traditional Class C space. We want >> to use those addresses rather than the addresses our ISP would give >> us. We have asked the ISP if they can announce a /24 out of that >> block, and they have said "sure". However, I have read here about >> announcement filtering. >> Will certain providers filter that /24? We have two reasons for >> using our own space. First, we can get redundancy by connecting with >> two ISPs and having them both announce the network (or have one >> announce if the other dies). >Multi-homing redundancy is a good thing, assuming that you have >undertaken multiple service entrances to your facilities, and prevented >your circuits from being "groomed" into the same cable elsewhere. >Several such concerns have been described recently on this list. >Otherwise, your multi-homing makes no sense. To the contrary. It doesn't make "no" sense...though it may make your multi-homing less effective than you hoped for. >Experience has shown that failures are more likely to occur in your >local facilities than in the provider(s). Maybe your experience...certainly not mine. The vast majority of downtime for IgLou is a result of upstream providers of some sort (LEC, IXC, ISP; usually ISP). Let's put a YMMV on this, shall we? >> Second, we can carve up our /20 in /24s and use them for different >> Internet POPs for our company (e.g. one in the states, one in Europe, one >> in the Pacific Rim, etc.). >A /20 that is split up into /24s should be filtered! Yet another overbroad statement. >REMEMBER: IP addresses are related to network TOPOLOGY, not your >company administration. Dividing a set of "related" addresses into >unrelated topology (split by oceans) increases the routing costs of >everyone else. Right, if their network topology (divided by oceans) connects to the Internet in multiple places, there will be multiple places announcing routes. Is it more efficient for all involved if they carve a /20 into smaller blocks, which at least have some chance of being aggregated at some point, or to use totally seperated blocks that have no chance of ever getting aggregated? -- Jeff McAdams Email: [email protected] Head Network Administrator Voice: (502) 966-3848 IgLou Internet Services (800) 436-4456
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