Discussion On Routing Modes IETF72 P2PSIP WG draft-jiang-p2psip-sep-01 Jiang XingFeng Carlos Macian Victor Pascual

Routing Modes Symmetric Recursive –Request and corresponding response follow the same path; –Adopted in the current RELOAD draft Direct Response –Send response directly back if the requesting peer allows it (e.g. it is publicly reachable) Relay Peer –With help from relay peers with unrestricted connections, the response could go through the relay peer to reach the request originator Forward Response –Response is considered as a distinct transaction from request and routed through the overlay based on the Node ID of request originator, (i.e. routing based on the underlying P2P algorithm) Iterative –where the intermediate peers merely return a response indicating the next hop, but do not actually forward the message to that next hop themselves

Why Relay Peer And Direct Response? Improve Success Rate NOT meant to REPLACE symmetric recursive –Enhancement to symmetric recursive –Could work together with symmetric recursive Main Benefit –Reduce the number of hops of response path to Number of hops = 1 - Direct Response Number of hops = 2 - Relay Peer –Improve success rate of P2PSIP transaction

Where Is Relay/Direct Response Helpful? Dynamic Scenarios Concerns about routing in P2P systems –Node’s stability –Connectivity stability between peers Where Symmetric MAY NOT Work Well –Heavy churn –Path with larger hop count The number of hops often follows a uniform distribution within [0, M]; M: lookup complexity of the specific algorithm in use Symmetric works well with smaller hop count –Stability of TURN peers has an impact on the connectivity stability between peers –Overlays with large scales, for example, over 1000 peers

How Relay Peer Works - 1 A B C D Z X Y Request Originator Intermediate Peer Destination Peer Relay Peer Pre-established connection Request Symmetric Recursive Relay Peer

How Relay Peer Works - 2 A typical message sequence –Originator discovers relay peers first –Originator carries info about relay peers in the request to be routed around the overlay –Destination peer sends the responses to the relay peers which forwards the response toward the request originator When Relay Peer is triggered –The destination peer decides whether or not Relay Peer is used –Possible criteria The request has traversed so many hops that it is highly probable that one of reverse connections broke down

Concerns – Relay Peer Relay Peer –Considered as a kind of service, just like STUN/TURN service; –Unrestricted connection – Identify Relay Peer Possible to decide whether a peer is on the public Internet in P2PSIP, for example, with the help from bootstrap peer or enrollment server who are already on public Internet; While being on the public Internet, a peer can use Direct Response to determine whether or not it is behind a firewall or address-independent firewall;

Concerns – DoS Attack Attack 1 –A large number of responses are sent to the Relay peer to overload the Relay peer Relay peer only forwards response to the peer with whom (peer) it has direct connections; Attack 2 –Malicious peers send a great number of requests and the destination peer may try using Relay Peer and symmetric recursive routing at the same time, which will amplify the number of the response to the request originator Destination peer will base response on some criteria treated as a parameter, such as total hops the request’s traversed, to decide whether relay peers are used to route the response; This mitigates the impact from the response amplification

Next Step –Adopted as a WG item (Direct Response and Relay Peer)? Or –The choice of Routing modes be a open issue and need more investigation? (including symmetric recursive)