DRAFT: Distributing K-Root Service by Anycast Routing of 193.0.14.129
Daniel Karrenberg
Date: November 2002
Abstract
This memo proposes to distribute the DNS service provided by k.root-servers.net
across multiple locations in the Internet topology. It discusses the motivation
for and the principles of implementation. A first inventory of detailed
issues is provided in an appendix.
Table of Contents
1.0 Introduction
DNS root name servers need to be accessible by Internet hosts in order
for the DNS to function properly. Accessibility is determined by the ability
of the server to handle a given query load and by the connectivity of
the server to the rest of the Internet.
The RIPE NCC operates k.root-servers.net (K-root) in the RIPE region
in order to help safeguard the quality of the DNS in the Internet and
in the RIPE region in particular. The RIPE NCC obtains guidance from RIPE.
For K-root, the connectivity issue has been addressed by placing it at
the LINX, a topologically very well connected point. The server load issue
has been addressed by deploying successive generations of hardware with
increased processing power and by distributing the load locally among
a number of machines at different LINX sites. A cold spare system has
been available in Amsterdam at all times to provide continuity in case
of catastrophic failures at the primary server location. Over the years
this set-up has provided very reliable service.
However, issues about differences in connectivity to the service across
the RIPE region have been raised repeatedly. A more distributed provision
of the service is generally seen as positive because of:
- lower network delays due to shorter paths between clients and servers,
- less dependence on connectivity to a single location,
- better load and DDoS attack resilience because of distributed servers,
- more overall redundancy.
For these reasons numerous organisations have offered to host additional
servers operated by the RIPE NCC. So far this has not been considered
because the number of unique IP addresses at which the service can be
provided is exhausted by currently assigned servers.
2. Scope of this Memo
This memo proposes to deploy multiple servers providing k.root-servers.net
name service across the RIPE region, each using the same IP address. This
is commonly called 'anycasting'. A detailed description of one implementation
can be found in RFC3258.
The intention of this memo is to establish the principles of this, inventarise
the major issues and request comments from the RIPE community and other
interested parties. An initial inventory of detailed issues is provided
as an appendix.
3. Proposal
Simply put, the RIPE NCC will provide K-root name service at multiple
locations dispersed over the Internet topology but at the same IP address.
No DNS client/resolver changes are necessary. The service will appear
exactly the same for the users. Normal Internet routing will distribute
the traffic among the different instances of K-root.
This will be implemented by installing multiple copies of the current
server sets at different points and announcing the current prefix 193.0.14/24
from these points.
The main challenge with this set-up is to ensure consistency:
- operation
All servers will be operated in a consistent way by the RIPE NCC. They
will have appropriate out-of-band access path to ensure that the operations
centre can access them.
- monitoring
The availability and responses will be monitored by dedicated monitoring
systems installed at multiple locations. Also the BGP propagation
of the prefix 193.0.14/24 will be monitored constantly by the existing
remote route collectors. [http://www.ripe.net/ris/]
Users will be able to identify the particular instance they are
using by published methods using DNS queries. [draft-ietf-dnsop-serverid]
- correctness
The correctness and authenticity of the root zone data will eventually
be guaranteed using DNSSEC. Until this can be deployed the current
method will need to be employed: ISPs will need to closely monitor
where they route traffic to 193.0.14/24 and from where they accept
traffic from that address. The RIPE NCC will publish and maintain
a list with the locations of the k-root instances, the BGP autonomous
system numbers of their immediate neighbours and any other information
that can help ISPs and others to ensure that they reach an authentic
instance of K-root. This list will be maintained until appropriate
routing security technology is widely deployed.
The RIPE NCC and K-root itself are well suited for this mode of operation.
IANA asked the RIPE NCC to operate K-root, the geographic and topological
location of K-root was not specified in any way other than "somewhere
in the RIPE region". The RIPE NCC was chosen because it is neutral
and professional but above all directly accountable to RIPE and its membership.
The location at the LINX was subsequently chosen based on evaluation
of the Internet topology in the region and a recommendation by the RIPE
DNS working group. Distributing K- root over a number of places is a natural
continuation of this policy.
In addition to operating K-root at a remote location the RIPE NCC has
considerable experience in operating distributed services. The Test
Traffic Measurements Service operates more than 80 machines all over
the world to collect performance measurements. Some of these can be used
to monitor the DNS service of K-root as well. The Routing
Information Service operates 9 remote route collectors at exchange
points all over the world to collect BGP routing information. These route
collectors will be used to monitor the routing of 193.0.14/24.
At any point in time there is a trade-off between the added benefit
of adding more servers and the difficulty of operating them consistently.
The optimal number of servers depends on a large number of constantly
changing factors. It needs to be evaluated continuously as things progress.
4. Operational & Funding Models
For the purpose of stability and for gaining experience, all instances
of K-root will be operated by the RIPE NCC. This ensures smooth transitions,
consistency and correctness of root zone data.
After the initial deployment, there are a number of possible operational
and funding models.
4.1. Traditional
Traditionally K-root operations have been part of general RIPE NCC activities
and thus have been collectively funded by the RIPE NCC membership. This
is an appropriate funding model as all members benefit from stable root
name service. It is also easy to administer. Difficulties may arise when
the number of locations is such that the operational costs increase very
significantly. Another important drawback of this model is that the number
of additional sites will be limited by available funds and the sites will
have to be determined by a selection procedure based on criteria including:
- position in Internet topology,
- position relative to existing K-root instances,
- local operations support,
- operational requirements [rfc2870],
- commitment to fund operations at a later stage.
4.2. Location Fees
The drawbacks of the traditional model can be largely overcome by charging
the organisations hosting K-root instances a fee that covers the operational
costs. This obviously scales better and requires less of a beauty contest,
because the funds available will more closely match the operational costs.
It is quite possible that the initial demand will be higher than the operational
capabilities of the RIPE NCC.
Also it should be observed that in funding and some other aspects this
is exactly the opposite of the traditional model: In the traditional model
the RIPE NCC pays facilities management fees to the hosts whereas in this
model the hosts pay.
Transition should be planned carefully.
4.3. Operated and Funded Decentrally
In this model anyone who wishes would be able to operate a K-root instance.
This model has such serious problems with guaranteeing stability and consistency
that it cannot be implemented today or in the near future. The minimum
requirement for this operational mode is a zone signing mechanism that
ensures consistency and authenticity of root zone data. Implementing this
also requires a changed model of service responsibility as it is obviously
impossible to hold any one entity responsible for the service. While this
may ultimately scale the best, it is extremely premature at this point.
We propose to continue with the traditional model for now and explore
other models while gaining operational experience. The associated selection
procedures will be executed by the RIPE NCC and guided by the relevant
requirements RFCs and the RIPE DNS working group.
5. Implementation Plan
5.1. Initial BGP change
The routing announcements of the current server prefix 193.0.14/24 will
change from AS5459 (LINX) to the dedicated new K-root autonomous system
number AS25152.
ISPs need to be aware of this and adapt their routing filters accordingly.
It is recommended that ISPs who do not already do so take precautions,
safeguarding that they receive this prefix from an authentic K-root via
a trusted path and that they route traffic to it via trusted paths as
far as possible. At the same time an initial set of BGP and DNS service
monitors will be deployed.
5.2. Move the Cold Standby to Service
The current cold standby server at the RIPE NCC will be activated as
a regular server. AS25152 will be announced also by the RIPE NCC at the
AMS-IX. As the server is already available and configured this can be
done fairly rapidly. The distribution of the load, BGP routing information
and other operational data will be gathered and evaluated. ISPs will have
the opportunity to test this set-up and provide feedback. In case of problems
the RIPE NCC instance of K-root will be deactivated quickly, returning
to the previous service level.
5.3. Implement Further Instances
While monitoring continuously a number of further instances of K-root
will be deployed. Currently we expect this to be about 5 additional instances.
This number is limited by operational and monitoring capacity. It is important
not to deploy more instances than can safely be operated and monitored.
Especially the capacity to detect and correct problems in this distributed
set-up needs to be carefully monitored.
5.4. Spreading Further
Planning further than this is currently difficult because of lack of
experience with distributed K-root operations and possible funding models.
Acknowledgements
The author would like to thank Joao Silva Damas for comments on an earlier
draft as well as Andrei Robachevsky and Henk Uijterwaal who provided comments
on recent drafts.
Appendix A - Detailed Issues
Using a router or having a server speak BGP?
Withdrawing BGP announcements based on service availability?
Distributed service monitoring: Using current RIPE NCC operated machines
all over the world is an easy option. Maybe distributing automatic monitoring
software to be run by volunteers is another. What is essentially needed
is to try a small number of queries periodically including the query identifying
the instance of the server. Then transmitting the results back to a (set
of) collection point(s).
Distributed BGP Monitoring: The RIS can be used for
this. Coverage should be sufficient.
Information Campaign: What is needed to reach all ISPs that need to know?
How long a lead time do they need for the various stages of the deployment?
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