Section: 11.2.1.3.4 IPv6 Router Configuration Variables
Content: For IPv6 Address Autoconfiguration to work properly , network entities which act as an access router towards the MS/UE, i.e. PDN GW, Serving GW, ePDG and TWAN, shall be consistent with the RFCs specifying this process (for example RFC 4862 [83] and RFC 4861 [89]), unless stated otherwise in this or other 3GPP specifications. RFC 4861 [89] specifies a set of conceptual router configuration variables. Some of these variables require particular attention in GPRS and EPC in order to preserve radio resources and MS/UE power consumption while still allowing for appropriate robustness and fast user-plane set-up time even in bad radio conditions, or simply because they have a particular meaning in GPRS and EPC. These particular variables are listed below with appropriate (default) values and shall be configurable per APN. The values specified hereafter are specific to GPRS and EPC, and supersede those specified in RFC 4861 [89]. MaxRtrAdvInterval Shall have a default value of 21 600 s (6 h). MinRtrAdvInterval Shall have a default value of 0,75 × MaxRtrAdvInterval i.e.16 200 s (4,5 h). AdvValidLifetime Shall have a value giving Prefixes infinite lifetime, i.e. 0xFFFFFFFF. The assigned prefix remains Preferred until PDP Context/Bearer Deactivation. AdvPreferredLifetime Shall have a value giving Prefixes infinite lifetime, i.e. 0xFFFFFFFF. The assigned prefix remains Preferred until PDP Context/Bearer Deactivation. RFC 4861 [89] also specifies a number of protocol constants. The following shall have specific values for GPRS and EPC: MAX_INITIAL_RTR_ADVERT_INTERVAL This constant may be a variable within GPRS and EPC. It may have a value that gradually increases (exponentially or by some other means) with the number of initial Router Advertisements sent. This will enable a fast set-up of the MS-GGSN or MS/UE-PDN GW/Serving GW/ePDG/TWAN links in most cases, while still allowing the MS/UE to receive a Router Advertisement within the initial phase, even in case of bad radio conditions or slow response time, without having to send a large number of initial Router Advertisements. MAX_INITIAL_RTR_ADVERTISEMENTS This is the number of Router Advertisements sent during the initial phase after the MS-GGSN or MS/UE-PDN GW/Serving GW/ePDG/TWAN links have been established. The value of this constant shall be chosen carefully, and in conjunction with MAX_INITIAL_RTR_ADVERT_INTERVAL, so as to not overload the radio interface while still allowing the MS/UE to complete its configuration in a reasonable delay. For instance, the default value could be chosen so that initial Router Advertisements are sent for at least 30 s. After the initial phase, the periodicity is controlled by the MaxRtrAdvInterval and the MinRtrAdvInterval constants.