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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)
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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
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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?
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NAT NAT text has been removed as there is no additional requirements for 802.16 based networks
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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
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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
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Way Forward We need WG inputs for default MTU value
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Backup Slides Details to arrive at 1400 bytes
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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
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GRE Overhead GRE Header – 4 bytes IP Header – 20 bytes Optional Headers – 12 bytes Total GRE Header – 24 to 36 bytes
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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
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Thank You
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