IPv6

Fest time at college - Good since I get lot of free time to spend around looking at routing tables. It’s always interesting since last week was full of some major submarine cable cuts and has huge impact on Indian networks.

Anyways, an interesting issue to post today about Global IPv6 routing . There are “dark spots” in global IPv6 routing because of peering dispute between multiple tier 1 ISPs involving Hurricane Electric (AS6939) & Cogent Communications (AS174).  What’s happening here is that both tier 1 providers failed to reach on agreement to keep peering up in case of IPv6. This has resulted in parts of global IPv6 internet where packets from one network (and it’s downstream) can’t reach other network or their downsteam singled hommed networks. 

Subnetting IPv6 sounds very complex but to be true - it is very easy! All you need to do is to understand basics of IPv6 addressesing - how an address is formed and how to efficiently use CIDR notation.   Firstly how an IPv6 address looks like? (good to clear fundamentals first!) An IPv6 address has 8 sections seprated by coloums and each sections has carries 4 hexadecimal digits. So an IPv6 address is something like: xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx - Each x can have a hexa decimal value i.e from 0 to 9 and a to f. Thus 16 possible values for each x. Since each each x is stored in binary i.e 0 or 1 (that is 2 possible value) - number of bits per section turns out to be 2x2x2x2 = 16bits. Thus we have now each section with 16 bits per section and 8 sections in total. This turns out to be 16 + 16 + 16 + 16 + 16 + 16 + 16 + 16 bits = 128bit. This is why an IPv6 address has 128bits. This means total possible addresses in IPv6 space is 2^128 = 340 282 366 920 938 463 463 374 607 431 768 211 456 addresses. Next, an important point to remember here is  - in IPv6 address clients are mostly based on /64 subnet which means first 64 bits go to network part while next 64 bits go to the host part i.e usage IPv6 addresses which are allocated to end machines.  

Just now completed IPv6 certification with Hurricane Electric. It was very much fun!

Starting was pretty much simple and basic, followed by email server running on v6 - which also I was doing already. I was stuck at most unexpected part - when I had to setup IPv6 based DNS servers. My first reaction was - that’s so simple….later on realized that system was just not accepting my entry and kept on giving error with AAAA records. Then suddenly I realized that I missed creating AAAA at DNS servers, but created only glue records which was causing issue. Created AAAA and that also went smoothly + glue helped me in final test too.