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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Re: Communities
On Tue, 16 Oct 2001, Niels Bakker wrote: > As already noted, currently communities are mostly used to control > advertisements of one's announcements by upstream providers, and not > for outbound routing, I'm sure it's used more for the former than the latter, however, there are networks that look at communities for outbound routing. A little more than I expected, even. This seems to happen mostly at multihomed networks. For instance we (AS12854) set a lower metric for routes that come in over a certain exchange point and a lower local preference for routes learned somewhere across the atlantic. > Customer A has a connection to upstream B and speaks BGP with B. B as > two different paths to C: one cheap and slow, one fast and expensive. > (This seems to be a business opportunity - devise lines that are both > cheap and fast.) Well, lines used to be both expensive and slow, so at least there is progress... > Now B can set communities on routes received from C based on where a > certain prefix was received. If they overlap, however, only the best > route out of the two will be passed on to customer A. Yes, this is always the problem with BGP. If I like low delay, but my upstream prefers a high bandwidth route that is also available for that destination, I don't get to see that nice low delay route I would have liked to use. > If this obstacle > is overcome, A still faces the problem of getting B to discern between > packets meant for either exit point to C. B could reengineer its > network to basically exist of two separate entities (a cheap one and an > expensive one) and let customers like A to connect to both, or extend > all its routers to have a pre-prefix source+destination routing table > entry to decide where to send packets. > This seems to need quite some engineering work. :-) B could also do away with layer 3 and sell layer 2 (or layer 1) connectivity to C, where each customer can select the appropriate quality levels. Other options are for B to focus on one selling point and try to optimize the network for that selling point, or use their expertise to find the perfect middle ground, or run several parallel networks.
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