Briefing paper: GPRS Infrastructure IP Addressing;

Source: Jarnail Malra, BT Cellnet
Date: 3^rd May 2000

References

1. Minutes: GPRS Infrastructure IP Addressing; Working Party Meeting #1 (held on 19^th April 2000)

Scope

This document is a briefing paper from the GPRS Infrastructure IP Addressing Working Party with the following objectives:

• Report on the outcome and the way forward resulting from a GPRS Infrastructure IP Addressing Working Party Meeting held on 19^th April 2000. The minutes [1] of these meeting are embedded in this briefing paper for reference.
• Provide initial details that are proposed to be added to IREG document, IR.33 as a change request relating to an IP addressing policy that will be applicable to GPRS infrastructure to enable roaming services to be supported.
• Identify proposed requirements for the GSM Association to maintain an IP-associated routing registry as part of the details in IR.21.

Meeting overview

• Held on 19^th April 2000
• Attending members had been invited from various disciplines from both the GSM and Internet communities, e.g. GSM operators (Europe and USA), RIPE, ISPs.
• Objective: To seek approval from the Internet Registry (IR) authorities for an addressing policy that could be used by all GSM operators to use public registered addressing in the GPRS infrastructure to enable GPRS roaming services to be supported.

Meeting outcome

The requirements for the addressing policy were identified and defined. These requirements will be submitted to the Regional Internet Registry Authorities to be ratified and formally accepted.

The policy is still only a set of draft proposals. It will be presented to the Local Internet Registry (LIR) working group at the next RIPE forum during 16/17 May 2000 as part of the process for its approval and steering it through to adoption.

It was identified that some operators were already in the process of configuring their GPRS networks to support a commercial service by Q2 2000, for which globally unique addressing is required in preparation to support roaming services. Public addressing will provide this unique addressing. However, the policy approval process with RIPE could, in the worst case, take several months to complete. Hence the following was proposed in the interim:

• Operators should initially utilise any public address space already assigned to them for use in the GPRS infrastructure.
• The host-master at the relevant IR authority should be notified for this re-use of address space to ensure their database records are accordingly updated.

Way forward for IREG

1. Addressing Policy integration within IREG documentation

The IP addressing policy will define the procedures and processes required to acquire and maintain public IP addresses for use in the GPRS infrastructure. All the GSM operators must adopt this policy in order to support GPRS roaming services.

The requirements identified in the addressing policy will be captured/referenced to a corresponding IREG document so that all the GSM community has visibility on how to meet their GPRS infrastructure requirements. It is proposed that IR.33 "GPRS Roaming Guidelines" be used for this purpose. BT Cellnet has offered its services to author a new section for this document, with an initial draft presented below for review and comment.

2. Proposed details Addressing Policy

The following are the initial recommendations for modification to the appropriate IREG document to define the IP addressing requirements and processes. It is emphasised that these recommendations are only proposals at this stage pending approval of the policy by the IR authorities.

• Public registered IPv4 addresses can be used for the GPRS infrastructure.
• Public IP addresses must be presented for network elements presented to and addressed by the networks of other operators across the inter-PLMN backbone during the roaming interaction process, e.g. SGSN, GGSN, DNS and border gateway.
• Existing request procedures supported by the IR authorities can be used to obtain IP addresses from their Local Internet Registry (LIR). Justification for the requested address allocation will need to be provided (typically a network configuration plan showing a two-year utilisation forecast of the address space requested). [IR authority to provide document/source reference for GSM operators to obtain copy of required processes]
• An inter-PLMN backbone network provider could become a LIR from which the operator could request their address space requirements. It should be noted that many of these providers already are LIRs and consequently have the necessary administration processes in place to arrange for address space allocation for the requesting operators.
• A GSM/GPRS operator can also apply to become an LIR. [IR authority to provide document/source reference for GSM operators to obtain copy of required processes]. This may be preferable for the larger operators. Other operators can then choose to request their IP addresses from the inter-PLMN backbone carrier or from a GPRS operator that has become an LIR.
• Where routing protocol BGP4 is used on the inter-PLMN backbone, 'Public' or 'Private' Autonomous System (AS) numbers could be assigned to the network of each operator. A Private AS number is proposed as the default scheme because the network elements involved during the roaming process can be considered to exist on a private network that will not be visible to the Internet. The following attributes are associated with the AS numbering scheme: -
• Both the Public and Private AS numbering scheme have their individual merits.
• Use of private AS numbers within the GSM community will require administration by a central body to ensure no two members could select the same AS number and thus consequently 'break' the BGP routing on the inter-PLMN backbone(s). This central body is proposed to be the GSM Association. Private AS number control/administration could be managed via IR.21 (see section on 'Routing Registry').
• A Private AS number must never be presented to the Internet.
• There is no dependency to use a Public AS number if Public addressing scheme has been deployed in the network, i.e. a private AS number can be associated with an operator's network, even though the network elements within that network have publicly addressed.
• There is no requirement for all operators to conform to a common AS numbering scheme, i.e. an operator could choose to use either a Public or Private AS number.
• The operator could also re-engineer their network at a later date to use an alternative AS number from the scheme originally selected, i.e. changing from a Private to Public AS number should be possible.

Routing Registry

It was proposed the GSM Association may want to consider maintaining a Routing Registry so that a centralised body could keep track of the routing details associated with each network operator.

The information recorded should include details associated with the IP addressing and routing that operators will need to know when configuring their networks to establish connections to other operators during the roaming process. Information such as the following should be recorded for each operator: -

• IP address space allocation
• IP addresses/APNs presented for all the network elements associated with roaming, e.g. SGSN, GGSN, DNS and border gateway
• Autonomous System number
• Contact names

It is proposed that the existing IREG document IR.21 "GSM Association operator details" be used to record the above information for each operator.