North American Network Operators Group

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Re: MPLS VPNs or not?

  • From: Walter Prue
  • Date: Tue Aug 07 18:13:45 2001

>Craig Partridge wrote:
>> the notion MPLS is faster to switch than IP reflects a poor
>> knowledge of router innards, or a poor router design.

David Charlap then wrote:

>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.

An aspect of MPLS routing that this may be overlooking is the fact that
MPLS tunnels can be designed with certain attributes which implement a
form of policy routing that normal least cost routing does not implement.
That is, blue packets can route over this link but not red packets unless
there is an outage of the S.F to N.Y. Link.  Another policy might say that
traffic from this customer may exit the backbone at only a few points. 
These engineered routing decisions are configured into an MPLS network so
these routing decisions are not made on a packet by packet basis.  Once
data is stuffed into an MPLS tunnel that was set up with certain policies
in mind you know that the data comes out at the other end.  Intermediate
nodes don't need to be convinced to "non-optimally" route this data but only
this data.