Saturday, May 16, 2009

Packet paths

Monitoring packet paths is an important component of sFlow monitoring. When a switch captures a packet header, it also captures the forwarding decision it made for the packet. The forwarding information includes the ingress and egress switch ports, VLANs and priorities, and if the packet is routed, subnet and next hop information is also provided. Additional information such as BGP AS path, MPLS tunnel and label stack will also be captured if it is relevant to the forwarding decision.

A traffic analyzer can thread together the path information from all the switches to provide a constantly updating network wide view of topology and the location of all hosts connected to the network.

The combination of packet header and packet forwarding data provides an integrated view of network traffic. For example, sFlow makes it possible to filter on forwarding attributes (VLAN , MPLS, route) and see traffic, or filter on traffic and identify forwarding paths. The integrated view of traffic makes it easy to answer questions such as: "Which links carry voice traffic?", "Is the voice traffic getting the correct priority value?" and "Who is sending traffic on a particular VLAN?"

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