Hello, On 10.6.2014 19:04, Blake Hudson wrote: > I haven't seen anyone bring up this point yet, but I feel like I'm > missing something... > I receive a full BGP table from several providers. They send me ~490k > *prefixes* each. However, my router shows ~332k *subnets* in the routing > table. As I understand it, the BGP table contains duplicate information > (for example a supernet is announced as well as all subnets within that > supernet) or excess information (prefix is announced as two /17's > instead of a single /16) and can otherwise be summarized to save space > in the RIB.
many people deaggregate their address space purposely, including large networks like Google, Akamai, Netflix etc. Full list for analysis like "who does that" is available at http://www.cidr-report.org/as2.0/aggr.html These days also some people split their allocated aggregatable space (PA) with different routing policies for each subnet, substituting old PI addresses (at least in RIPE region). Technically nothing blocks this and politically - it's up to each, what accepts. But some unreachable subnet means problems with customers... There's no summarization in hardware/software from RIB to FIB. From the vendor perspective, they would like to sell you new hardware with larger TCAMs/etc, of course... :-) With regards, Daniel
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