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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Re: MPLS VPNs or not?
Craig Partridge wrote: > > the notion MPLS is faster to switch than IP reflects a poor > knowledge of router innards, or a poor router design. Or just outdated information. It wasn't too long ago that IP best- match lookup hardware couldn't do line-rate at the high speeds needed in the cores of large networks. At that time, ATM was able to do line- rate forwarding at those speeds. This is one of the reasons that ATM was adopted in those networks. One of the big reasons for ATM's speed is its use of fixed-length VPI/VCI header lookups instead of variable- length IP best-match lookups. MPLS, thanks to its use of a fixed- length label header lookup has the same advantage. Over time, however, this advantage disappeared. IP best-match lookup chips were developed that could do a proper IP lookup at full line rate for OC-48 and even OC-192. With line-rate IP lookup, it's no longer possible for something else to be faster. It is possible that the pendulum may swing back the other way in time, of coruse. It is possible that IP lookup chips that can handle the next generation of line rate may not become available in a timely manner, which would once again give the advantage to fixed-length header lookup chips. But not having a crystal ball at hand, I have no idea if this is actually going to happen or not. -- David
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