IP QoS value was altered in packets

The IP QoS value set on outbound packets was altered by some intermediate device.

Recommended action

  1. Review test results along entire path.
  2. Identify where the IP QoS value was first altered.
  3. Review the configuration of devices identified.

Detailed explanation

Various methods exist to implement QoS (Quality of Service) within a network. In one approach, hosts and routers can set a QoS value in the IP datagram header as part of the overall implementation. This value can determine the per-hop behavior (PHB) a packet experiences at each node. However, some devices do not respect this field and alter the value. This is one way that QoS can be compromised.

Depending on its usage, this QoS field is known either as TOS (Type of Service) as per RFCs 791 and 1349, or Differentiated Services (DS) as per RFC2474. The altering of the value in this field does not guarantee that QoS is broken, but should be investigated if usage of this field is important to your application.

Possible secondary messages

  • "QoS mechanism may be affected"
  • "The resulting QoS value could not be determined"

Other resources