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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Re: Scalability issues in the Internet routing system
On Oct 18, 2005, at 11:30 AM, Andre Oppermann wrote: Especially since this does not have to be done in real time. BGP updates can take many seconds to process without end users thinking anything is amiss.1. The number of prefixes*paths in the routing table and interdomain routing system (BGP) This problem scales with the number of prefixes and available paths to a particlar router/network in addition to constant churn in the reachablility state. The required capacity for a routers control plane is: capacity = prefix * path * churnfactor / second I think it is safe, even with projected AS and IP uptake, to assume Moore's law can cope with this. You are mistaken in one of your assumptions. The FIB is generated asynchronously to packets being forwarded, and usually not even by the same processor (at least for routers "in the core"). Therefore things like pps / link speed are orthogonal to longest match. (Unless you are claiming the number of new prefixes is related to link speed. But I don't think anyone considers a link which has nothing but BGP updates on it a realistic or useful metric.2. The number of longest match prefixes in the forwarding table This problem scales with the number of prefixes and the number of packets per second the router has to process under full or expected load. The required capacity for a routers forwarding plane is: capacity = prefixes * packets / second This one is much harder to cope with as the number of prefixes and the link speeds are rising. Thus the problem is multiplicative to quadratic. Here I think Moore's law doesn't cope with the increase in projected growth in longest prefix match prefixes and link speed. Doing longest prefix matches in hardware is relatively complex. Even more so for the additional bits in IPv6. Doing perfect matches in hardware is much easier though... -- TTFN, patrick
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