Remove Multihoming Requirement for AS Number Assignments

Summary of Proposal

The current policy assumes that an Autonomous System and its peerings are globally visible, with the Autonomous System being multihomed with at least two others. However, there are situations when a globally unique AS Number is required and one or both of these presumptions are incorrect. Limited visibility is observed in the context of GRX peering, or a more common case: a network might be its own upstream, which supports reducing the peering requirement from two to one.

A common practice these days (observed by the authors) is to have the AS applicant fill in as peerings: 1) the AS Number of the actual provider, and 2) a route collector with a globally unique ASN. The authors believe that there is value in aligning the policy with reality, rather than continuing in the current, less transparent way.

The authors expect that the RIPE NCC, when needed, will present an aggregated view of AS needs for community consideration. Examples of typical needs would be: RFC 1930, RFC 2270, multihoming, preparing to multihome (when second provider is as-of-yet undeciced), connecting separately maintained private networks, and private networks where the uniqueness of a private ASN cannot be guaranteed.

Policy Text

[The following text will update section 2.0 in the RIPE Policy Document “Autonomous System (AS) Number Assignment Policies", if the proposal reaches consensus.]

a. Current policy text

2.0 Assignment Criteria

In order to help decrease global routing complexity, a new AS Number should be used only if a new external routing policy is required, see RFC 1930.

A network must be multihomed in order to qualify for an AS Number.

When requesting an AS Number the routing policy of the Autonomous System must be provided. The new unique routing policy should be defined in RPSL language, as used in the RIPE Database.

The RIPE NCC will assign the AS Number directly to the End User upon a request properly submitted to the RIPE NCC either directly or through a sponsoring LIR.  AS Number assignments are subject to the policies described in the RIPE NCC document entitled “Contractual Requirements for Provider Independent Resource Holders in the RIPE NCC Service Region”.

b. Proposed policy text

2.0 Assignment Criteria

A new AS Number is only assigned when the End User has a need that cannot be satisfied with an existing AS Number. RIPE NCC will record, but not evaluate this need.

To discourage excessive resource consumption, the sum of AS Numbers assigned to a single organisation must not exceed 1,000.

When requesting a 16-bit AS Number, the network must be multihomed within nine months of the assignment. Failure to multihome within this timeframe will result in deregistration of the assignment. A 32-bit AS Number is exempt from the multihoming requirement.

The routing policy of an Autonomous System should be defined in RPSL in the RIPE Database.

The RIPE NCC will assign the AS Number directly to the End User upon a request properly submitted to the RIPE NCC either directly or through a sponsoring LIR. AS Number assignments are subject to the policies described in the RIPE Document “Contractual Requirements for Provider Independent Resource Holders in the RIPE NCC Service Region”.

Rationale

a. Arguments supporting the proposal

• In the context of layer-3 MPLS VPN, you may wish to run eBGP on the CE both in the PE's direction and the CustomerLAN's direction. The Service Provider's PE has your regular ASN, and every CE in the network could share the same AS Number via use of as-override function and Site of Origin community.  But a Private AS Number might not be a good candidate, as the CustomerLAN may already use that AS Number.  With the current policy you are forced to evaluate CE configuration in each case, creating unnecessary complexity.
• A network might not be multihomed today, but wants to prepare all infrastructure so it can multihome at a moment's notice, or have some form of mobility in terms of suppliers.
• The accuracy of the RIPE Database is more important than anything. The authors suspect that already today organisations deem the value of obtaining a globally unique ASN higher than providing truthful information regarding its peers to the RIPE NCC. By simply not requiring potentially falsified information the process's transparency is increased.

b. Arguments opposing the proposal

• Could it be that previously aggregated prefixes are unbundled and, under the new policy, the fragments are originated by a set of Autonomous Systems with a single, common upstream?

Authors' remarks

The "1,000 ASNs per organisation" anti-hoarding number is based on the following: at the moment of writing, the largest amount of ASNs a single organisation has is 100. Setting the number at ten times the current maximum usage will allow for growth but prevent a single organisation from consuming all resources.

Note: In order to provide additional information related to the proposal, details of an impact analysis carried out by the RIPE NCC are documented below. These projections are based on existing data and should be viewed as an indication only.

A. RIPE NCC's Understanding of the Proposed Policy

The proposed policy asks the RIPE NCC to assign a new AS Number if an End User has a need that cannot be satisfied with an existing one. It also requires that the RIPE NCC record this need but not evaluate it.

It will be the End User that decides if this need is technically reasonable. The RIPE NCC will have no mandate to review the End User’s decision.

The proposal introduces a limit of 1,000 ASNs that can be assigned to a single organisation.

The proposal adds a special requirement that 16-bit ASNs must be multihomed within nine months of their assignment. Failure to comply with this requirement will result in deregistration of the resource. The RIPE NCC will apply the existing deregistration procedure.

The proposal removes the requirement that the routing policy be new and unique. It also makes optional the requirement that the routing policy be provided to the RIPE NCC.

B. Impact of Policy on Registry and Addressing System

An increased consumption of ASNs is a possible outcome if the proposal is accepted. It is hard to project the actual increase, as there is no historical data indicating how many organisations did not request an ASN, or requested an ASN with incorrect information due to technical requirements not described in the current policy.

This potential increase in consumption concerns especially the RIPE NCC’s pool of 16-bit ASNs, which is almost exhausted. The proposal tries to mitigate this risk by requiring that 16-bit ASNs be multihomed after nine months.

The RIPE NCC would like to highlight a possible effect of two other ongoing proposals 2014-13, "Allow AS Number Transfers" and 2014-05, "Policy for Inter-RIR Transfers of Internet Resources". If these proposals are accepted, ASNs could be transferred at any time after they have been assigned. The proposed nine-month requirement might therefore not be enough to prevent the 16-bit ASN pool from depleting faster than expected.

Fragmentation/Aggregation:

After analysing the data that is currently available, the RIPE NCC does not anticipate any significant impact if this proposal is implemented.

C. Impact of Policy on RIPE NCC Operations/Services 

Registration Services:

Amount of Requests and Workload 

The RIPE NCC expects AS Number assignment requests to increase due to the more relaxed criteria. Despite the removal of the need evaluation by the RIPE NCC, it is expected that the overall workload will be higher.

This is due to:

• An expected increase in new AS Number requests
• All new 16-bit AS Number assignments will need to be checked for multihoming nine months after the assignment has been made
• Additional deregistration of non-multihomed 16-bit AS Number assignments
• Additional checks to make sure a single organisation does not exceed 1,000 ASNs

Multihoming Requirement for 16-bit AS Numbers

The proposal requires that 16-bit ASNs be multihomed within nine months from the date they are assigned. The RIPE NCC would need to validate this to ensure compliance with the policy. This requirement would only apply to assignments made after the proposal was implemented. 

The RIPE NCC would like to highlight that the proposed policy would allow 16-bit ASNs to be requested for any need that cannot be satisfied with an existing AS Number, yet also requires that they be multihomed within nine months. To avoid surprises, the RIPE NCC will therefore warn End Users requesting 16-bit ASNs for reasons other than multihoming that they must be multihomed within nine months.

After nine months the RIPE NCC will perform a multihoming check by looking first at the number of peering partners visible in the global routing table. If this doesn’t show at least two peering partners, the RIPE NCC will follow up with the resource holder to see if the AS Number is being used for local peering. If at least two peering partners can still not be identified, the 16-bit AS Number will be considered as not multihomed.

The RIPE NCC will apply the existing deregistration procedure to 16-bit AS Number assignments that fail to meet this requirement. The final deregistration will occur a further three months after the nine-month multihoming check is conducted. Following the failed check, the RIPE NCC will notify End Users that their assignment will be deregistered in three months if it is not multihomed before then.

Need Requirement

The proposal asks the RIPE NCC to assign a new AS Number if an End User lists “a need that cannot be satisfied with an existing AS Number”. The RIPE NCC will not evaluate this need, but will ask that it be provided, in order to create statistics to inform the RIPE community.

Billing/Finance Department:

After analysing the data that is currently available, the RIPE NCC does not anticipate any significant impact if this proposal is implemented.

RIPE Database:

After analysing the data that is currently available, the RIPE NCC does not anticipate any significant impact if this proposal is implemented.

D. Legal Impact of Policy

The proposed policy requires a new AS Number to be assigned if an End User states a need cannot be satisfied with an existing AS Number. The RIPE NCC will not evaluate this need. The RIPE NCC will also no longer require the routing policy of the Autonomous System to be submitted.

The RIPE NCC will, however, evaluate whether this request complies with the other policy criteria. In particular, the RIPE NCC will check whether the request exceeds the 1,000 ASN limit as set by the policy.

The RIPE NCC will also check whether 16-bit AS Numbers fulfill the nine-month multihoming requirement. Again, this is not an evaluation of the need, but rather compliance with the policy criteria. 16-bit AS Numbers that fail to fulfill this requirement will be deregistered.

E. Implementation

The RIPE NCC estimates that the implementation of this proposal would have a medium impact. Processes, supporting software and documentation would need to be updated to allow the assignment of AS Numbers according to the new policy criteria, and for checking 16-bit ASN assignments for multihoming. The RIPE NCC would also need to develop a process for the collection and provision of statistics concerning the different needs behind AS Number requests.