8.1 Complications Introduced by Split Paths

8.1 Complications Introduced by Split Paths

If a router or other network element has access to all of a flow's packets, then the harm that router can do to a flow by changing the ECN field is no greater than the harm it could cause by simply dropping all of a flow's packets. However, in some scenarios a malicious or corrupted router could have access to only a subset of packets in a flow. The question is as follows: Can that router, by changing the ECN field in the subset of packets that it can access, cause greater harm to that flow than it could cause by simply dropping that set of packets?

This is also discussed in more detail in Section 18, with the following conclusion: indeed, an adversary with access to only a subset of packets in an aggregate could, by subverting ECN-based congestion control, be able to deny the benefits of ECN to other packets in the aggregate. While this is undesirable, it is not a sufficient concern to argue for disabling ECN.