signaling messages contain some sort of flow identifier that is associated with a specified behavior (e.g., a particular flow experiences QoS treatment or allows packets to traverse a firewall). An adversary might, therefore, use IP spoofing and inject data packets to benefit from previously installed flow identifiers.
We will provide an example of the latter threat. After NSIS nodes along the path between the NSIS initiator and the NSIS receiver processes a properly protected reservation request, transmitted by the legitimate user Alice, a QoS reservation is installed at the corresponding NSIS nodes (for example, the edge router). The flow identifier is used for flow identification and allows data traffic originated from a given source to be assigned to this QoS reservation. The adversary Eve now spoofs Alice's IP address. In addition, Alice's host may be crashed by the adversary with a denial of service attack or may lose connectivity (for example, because of mobility). If Eve is able to perform address spoofing, then she is able to receive and transmit data (for example, RTP data traffic) that receives preferential QoS treatment based on the previous reservation. Depending on the installed flow identifier granularity, Eve might have more possibilities to exploit the QoS reservation or a pin-holed firewall. Assuming the soft state paradigm, whereby periodic refresh messages are required, Alice's absence will not be detected until a refresh message is required, forcing Eve to respond with a protected signaling message. Again, this attack is applicable not only to QoS traffic, but also to a Firewall control protocol, with a different consequence.
The ability for an adversary to inject data traffic that matches a certain flow identifier established by a legitimate user and to get some benefit from injecting that traffic often also requires the ability to receive the data traffic or to have one's correspondent receive it. For example, an adversary in an unmanaged network
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