Document in OsmoGGSN User Manual the IPv6 allocation process over GTP
This process is a bit special and it makes sense to have it documented in a section in the osmo-ggsn user manual for users of the program to understand better the network setup and protocol traces.That basically involves:
- GGSN sending a Interface Identifier (IPv6 EUA) back to the SGSN during CreatePdpCtxResponse
- At the SGSN, higher 64 bits dropped, lower 64 bits used to create a link local address which is used to sent a ICMPv6 RouterSolicitation to multicast addr.
- GGSN sends back an IPv6 prefix when answering with ICMPv6 Router Advertisement
- MS/SGSN using that IPv6 prefix to set a global source address and use that to send data.
In order to understand the scenarios better, one can have a look at TTCN3 GGSN_Tests teststuite or manually reproduce it with sgsnemu or a real SGSN + MS.
Related interesting osmo-ggsn commits adding support for it: