Traffic Matrix Statistics

Not surprisingly, TMS is pretty good at building a traffic matrix. TMS is a simple, low-overhead method of gathering statistics about packets entering and traversing your network. It is an extension to CEF accounting that lets you collect information about the number of packets and bytes destined for a particular nonrecursive prefix. Both TMS and NetFlow count traffic, but TMS sacrifices some of NetFlow's granularity in exchange for a lower-overhead method of gathering the same kind of information. TMS works with both IP packets and MPLS-labeled packets.

TMS allows you to gather information about the following:

• The number of packets and bytes switched toward a given nonrecursive prefix

• Information about "internal" and "external" traffic (discussed later)

• BGP next-hop and neighbor AS information for a given destination network

You can gather this information for both IP packets and labeled packets.

TMS is based on Cisco Express Forwarding (CEF). CEF uses the concept of a nonrecursive prefix. A nonrecursive prefix is essentially a route that was not learned via BGP. IGP-learned routes, static routes, and directly connected routes are all examples of nonrecursive prefixes. A few nonrecursive prefixes are not in the routing table (CEF has the concept of a host adjacency, which is a /32 prefix installed for a host on a broadcast network, such as Ethernet), but generally speaking, nonrecursive prefixes are non-BGP routes.

You can see a router's nonrecursive prefixes using show ip cef non-recursive, as shown in Example 101.

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