1. IPv4 over IEEE 802.16 IP CS draft-ietf-16ng-ipv4-over-802-dot-16-ipcs-02 Syam Madanapalli Ordyn Technologies 71st IETF - Philadelphia, PA, USA (March 9-14, 2008)

2. Background  WG item  Currently in WGLC  Issue from the last IETF – Minor: ARP - should be similar to any other P2P modelsARP - should be similar to any other P2P models NAT – No additional requirements for 802.16 based networksNAT – No additional requirements for 802.16 based networks – Major: Default MTU - whether it should be 1500 bytes or lessDefault MTU - whether it should be 1500 bytes or less

3. ARP  ARP text has been reworded to imply that the procedures are same as any other point-to-point link models  But what if a host initiates an ARP packet? – Should we add any text for implementers?

4. NAT  NAT text has been removed as there is no additional requirements for 802.16 based networks

5. Default MTU: Two Approaches  1500 bytes to align with RFC 5121 – Packet fragmentation between BS and ASN GW (AR) in WIMAX – Requires MTU discovery procedures like DHCP Option 26DHCP Option 26 Path MTU discovery (RFC 1191 )Path MTU discovery (RFC 1191 ) Packetization Layer Path MTU Discovery (RFC 4821)Packetization Layer Path MTU Discovery (RFC 4821) But it these are not mandatory/widely implementedBut it these are not mandatory/widely implemented  1400 bytes to accommodate GRE/IPSec overhead – Avoids fragmentation in most cases

6. Default MTU: Mailing List Discussion  Recommendation to choose maximum possible value i.e. 2038 bytes for MTU – Only air-link consideration is not sufficient as the IP link represent to host to AR

7. Way Forward  We need WG inputs for default MTU value

8. Backup Slides Details to arrive at 1400 bytes

9. ESP Overhead  ESP Header – 8 bytes  Initialization Vector – 0 to 16 bytes  ESP Trailer – 16 bytes  Total overhead = 40 bytes (max) – Tunnel mode: adds 20 more bytes  Padding – 0 to 255 bytes – DES/3DES – upto 7 bytes – AES – upto 15 bytes – SHA1/MD5 – upto 63 bytes

10. GRE Overhead  GRE Header – 4 bytes  IP Header – 20 bytes  Optional Headers – 12 bytes  Total GRE Header – 24 to 36 bytes

11. Typical GRE+IPSec Overhead Tunnel Combination Specific MTU Required Recommended MTU GRE+IPSEC (Transport Mode) 14401400 GRE+IPSEC (Tunnel Mode) 14201400 Source: Resolve IP Fragmentation, MTU, MSS, and PMTUD Issues with GRE and IPSEC http://www.cisco.com/warp/public/105/pmtud_ipfrag.html

12. Thank You