A Lightweight Opportunistic Tunneling

We present LOT, a lightweight ‘plug and play’ secure tunneling protocol deployed at network gateways. Two communicating gateways, A and B, running LOT would automatically detect each other and establish an efficient tunnel, securing communication between them. LOT tunnels allow A to discard spoofed packets that specify source addresses in B’s network and vice-versa. This helps to mitigate many attacks, including DNS poisoning, network scans and most notably (Distributed) Denial of Service (DoS). LOT tunnels provide several additional defenses against DoS attacks. Specifically, since packets received from LOT-protected networks cannot be spoofed, LOT gateways implement quotas, identifying and blocking packet floods from specific networks. Furthermore, a receiving LOT gateway (e.g., B) can send the quota assigned to each tunnel to the peer gateway (A), who can then enforce near-source quotas, reducing waste and congestion by filtering excessive traffic before it leaves the source network. Similarly, LOT tunnels facilitate near-source filtering, where the sending gateway discards packets based on filtering rules defined by the destination gateway. LOT gateways also implement an inter-gateway congestion detection mechanism, allowing sending gateways to detect when their packets get dropped before reaching the destination gateway and to perform appropriate near-source filtering to block the congesting traffic; this helps against DoS attacks on the backbone connecting the two gateways. LOT is practical: it is easy to manage (‘plug and play’, requires no coordination between gateways), deployed incrementally at edge gateways (not at hosts and core routers), and has negligible overhead in terms of bandwidth and processing, as we validate experimentally. LOT storage requirements are also modest.