1. L3A: A Protocol for Layer Three Accounting Alwyn Goodloe, Matthew Jacobs, Gaurav Shah University of Pennsylvania Carl A. Gunter University of Illinois

2. SOHO to Enterprise Example HomeInternetOffice CAPVPNS WPA to AP Ipsec to Office SSH to Server Three levels of Authentication and Encryption! Address Translators And Firewalls

3. Multi-Tunnel Configuration Application Protocols to set up Tunnels/ Security Objectives Of Tunnels N/W Security/ Key Exchange

4. Cramming Attacks ClientServer Accounting System Attacker E2E Security Tunnel Network Access Server (NAS) NAS Security Tunnel Unauthenticated Ingress

5. Countermeasures Add difficult-to-discover state to return port. Problematic: On-path attackers Establishing sufficient state Example: Network Address Translation (NAT) Determined by four flow parameters Well known destinations give strategies for server ports and addresses Weaknesses in NAT parameter selections Brute force: 10,000 pkts/sec on stock machine Observed 7 minutes for timeout

6. Tunnel as Countermeasure Challenge: Coordinate the creation of the tunnels

7. Related Work Accounting Simple Network Management Protocol (SNMP) RADIUS Juniper Networks: GPRS gateway provides protection against “over-billing” attacks Tunnel Configuration Solsoft Policy Server Z. Fu and S.F. Wu 2001 Cisco Dynamic Multipoint VPN (DM VPN) Cisco Tunnel Endpoint Discovery (TED)

8. L3A Set-Up Client NAS Server Req(cred) Ack(cred) Fin SPD C  S:(C  N) SPD S  C:(S  N) SPD:S  C:(S  N)

9. L3A Set-Up With Reuse Client Server1 Server2 NAS Req(Cred) SPD C  S2:(C  N) SPD S2  C:(S2  N) Ack(cred)

10. L3A Tear-Down

11. Implementation Micron 600MHz Pentiums, 128 MB memory in C/S and 256 in NAS, 100 Mbps Ethernet links FreeBSD 4.8, OpenSSL crypto, PF_KEY interface to SPD IKE- our implementation of IKEv2 with support for nested tunnels

12. IKE-

13. Performance Measurements Throughput How does L3A bulk transmission compare to no accounting or other approaches to accounting? Latency How does L3A set-up compare to other approaches in ms required for set-up and tear-down? Both measured for a single client and server; NAS was only lightly loaded.

14. Throughput Cases Base – no security End-to-end – IPsec with encryption and authentication between client and server Typical – IPsec E2E and IPsec with encryption and authentication between client and NAS L3A – E2E and authenticated tunnels between client and NAS NAS and server

15. Throughput L3A is 100% faster than typical L3A is 32% slower than no accounting

16. Latency Cases End-to-end – IPsec IKE- from end to end L3A without reuse L3A with reuse of client to NAS tunnel

17. Latency Latency to establish tunnels for accounting is 142% greater than end-to-end protection alone, but In the most common case, it will be only 48% longer.

18. Conclusions Introduced concept of cramming attacks Reviewed possible countermeasures and did penetration study of NAT Proposed L3A protocol Implementation shows reasonable performance Main contribution: progress on how to design multi-tunnel protocols

19. L3A Messages

20. Cramming Attacks