1. TCP Performance over IPv6 Yoshinori Kitatsuji KDDI R&D Laboratories, Inc. kitaji@kddilabs.jp

2. Summary Background Experiment –inside of Tokyo XP, –between Osaka University and Tokyo XP –TransPAC Northern Route Lesson & Learn

3. Background Although IPv4/IPv6 dual stack in APAN Tokyo XP and TransPAC link northern route started in 2001, there was no performance test. –Two main routers (Juniper M20) in Tokyo XP, GigabitEthernet, PoS Osaka University was planning DV over IPv6 demonstrations in iGrid2002 and HDTV over IPv6 in SuperComputing2002 –iGrid2002 University Osaka deliveries the DV streams over IPv6 to Amsterdam University (Venue), San Diego Supercomputer Center and Abilene, APAN Tokyo XP, ASCnet, JGNv6, TransPAC, SURFnet 100Mbit/s for 3 DV streams –SC2002 University Osaka deliveries the HDTV stream and stream over IPv6 to SCInet (Venue in Baltimore) and San Diego Supercomputer Center Abilene, APAN Tokyo XP, JGNv6, TransPAC 140Mbit/s for a HDTV stream and a DV stream

4. Experiment Inside APAN Tokyo XP –2 Juniper M20 connected with GigabitEthernet link Path between APAN Tokyo XP and Osaka University –Osaka University connects to JGNv6 TransPAC links (IPv4) –Northern route to Seattle is POS OC12 link

5. Juniper M20 Examination1 Inside of APAN Tokyo XP –Routers and Switches are connected with Gigabitethernet –PCs Pentium III 1GHz 1GB Memory 64bit 66MHz PCI Linux Usagi kernel 2.4 –TCP options Window Size: 128KB Enable SACK –Result 750-900Mbit/s depends on the regular traffic of users Chicago Seattle Juniper M20 Foundry BigIron 4000 Foundry NetIron400 PC Foundry FastIron 400 GigabitEthernet

6. PC Examination2 Path between Tokyo XP and Osaka University –Osaka University is connects to JGNv6 JGNv6 is ATM OC12 network –PCs Pentium III 1GHz 1GB Memory 64bit 66MHz PCI Linux Usagi kernel 2.4 –TCP options Enable Window scaling & SACK –Result1: Tokyo XP--Osaka University 170Mbit/s Window size: 200KB RTT: 15ms –Result2: Tokyo XP --JGN ROC 750-900Mbit/s Window size: 128KB –Result3: JGN ROC – Dojima DC 170Mbit/s Window size: 180KB-1MB RTT: 15ms Bottleneck is the link between JGN ROC and Dojima DC Hitachi GR2000 Juniper M20 APAN Tokyo XP Osaka University JGN Research and operation Center Hitachi GR2000 PC Test1 Test2 Test3 JGNv6 Dojima DC ATM OC12 Juniper M20

7. PC Examination3 PC APAN Tokyo XP Path between Tokyo XP and TransPAC in Seattle –TCP over IPv4 –The link is POS OC12 –PC in Tokyo XP Pentium III 1GHz 1GB Memory 64bit 66MHz PCI Linux Usagi kernel 2.4 –PC in TransPAC Pentium III 866MHz 768MB Memory 64bit 66MHz PCI Linux kernel 2.4 –TCP options Window size: 8MB Enable SACK RTT: 114ms –Result: 360 – 460 Mbit/s Window size: 16MB RTT: 114ms –Upstream was not available. Security policy of PC in Seattle…? POS OC12 TransPAC Juniper M20 Juniper M5

8. Examination3 (cont.)

9. Learn with experiments Enabling TCP option –Same as IPv4 Window scaling (for maximum 8MB) –net.ipv4.tcp_window_scaling = 1 –net.ipv4.tcp_rmem="4096 87380 4194304 –net.ipv4.tcp_wmem="4096 65536 4194304" –net.core.wmem_max=8388608 –net.core.rmem_max=8388608 –net.core.wmem_default=65536 –net.core.rmem_default=65536 Selective Acknowledgement –net.ipv4.tcp_window_scaling=1 Congestion avoidance of Linux is also same –Unavailable SACK with FreeBSD (same as IPv4) Hop by hop measurement environment is important –End to end measurement doesnt solve where problem lies Loss, Loss and Loss… –buffer allocated by driver for NIC in PC should be enlarged Linux: ifconfig txqueuelen FreeBSD: depends on driver –Usually change parameter in source code of driver and reconstruct kernel –synchronization failure (in JGNv6) Usually ATM switch generates clock and Router follows with it. Wrong configuration. Non-shaped Multiple PVCs in a Physical link cause congestion. packet loss…

10. Slow Start Threshold Switch to congestion avoidance algorithm here, due to ssthresh was cached in the past. After this, bandwidth increase linearly.