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Services | Backbone operation | Technologies | R&D | Networks | Qualification | Events |
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1. Abstract
1. AbstractThis document shows CAIS's (Security Incident Response Team) proposal to implement NTP's (Network Time Protocol) hierarchy in RNP's backbone. In items 2 and 3 we provide the background and motivation justifying the project as a whole, showing the importance of implanting an NTP hierarchy which allows the synchronization of the computers and network equipment connected to RNP's backbone. In item 4 the model that will be used to implant such a hierarchy is presented in details. We list aspects that should be considered in the process of choosing the servers with which to synchronize and propose a policy of access to NTP servers based on the level (stratum) on which these servers will operate. In item 5 we discuss some pre-requisites to be considered when choosing the place to host the NTP stratum 1 server. Some complementary details, such as the operational system and NTP version to be used to implement the servers of NTP hierarchy, are mentioned in item 6. In item 7 we show a proposal of monitoring of NTP hierarchy. Finally, item 8 presents the results expected after the implantation of NTP hierarchy. 2. MotivationNTP - Network Time Protocol - servers allow their clients to synchronize their computer clocks as well as other kinds of network equipment using a standard reference of time accepted worldwide, known as UTC (Universal Time Coordinated). In the broad Internet, time synchronization is crucial to millions of computers exchanging information: people sharing databases, processing several kinds of transactions (such as: e-commerce, personal banking), etc. It is exactly in this environment of open information sharing that the need for a common time reference, which can be precise and reliable, becomes essential. Suppose, for example, that it is the deadline to send the Income Tax declaration, the clock of the machine hosting Federal Reserve's website is one minute fast and the time limit to perform this operation expires at 8:00 p.m. Any declaration sent after 7:59 p.m. will be rejected, causing damage to the contributor. Delays of up to one or two minutes are rather common when an NTP scheme is not used. From the point of view of network administration, using NTP is clearly an advantage since it permits automatic synchronization of all the equipment that is hooked up. In other words, the administrator does not have to go from machine to machine setting the local clock. In terms of security, clock synchronization of the several computers connected to the Internet is vital. Many times it has not been possible to determine certain events occurring in different nets due to the clock synchronization of their computers, which makes the logs register times which are inconsistent among themselves. In general, it has been noticed that the more complex the distributed applications implemented by means of the Internet, the more significant the quality of time synchronization in the Internet. 3. BackgroundIn Brazil, the use of NTP servers for synchronization is still very incipient. A recent study of NTP servers in the Internet Internet, rmade by Nelson Minar, shows that both NTP stratum 1 and stratum 2 servers are hardly used in the country. Up to now, no public NTP stratum 1 server has been available in the country, therefore making RNP's initiative the first of this kind. What is known is that, in the sphere of the Steering Committee, a similar initiative is being discussed, the one to implant an NTP stratum 1 server on the atomic clock of the National Observatory. Regarding stratum 2 servers, Minar's report also indicates that in addition to the fact that there are very few of them, in most cases there is no organized hierarchy nor a defined access policy associated to them. On the other hand, although there are no access restrictions to them, these servers are not usually made known to the public. Dave Mills, one of the most active contributors to the development of NTP protocol and current maintainer of NTP's homepage, includes in this website the official lists of stratum 1 and stratum 2 public servers spread worldwide. At present, there is no Brazilian NTP server catalogued there. In terms of RNP, in 1998, CAIS - RNP's Security Incident Response Team - permitted the implantation of stratum 2 and 3 NTP servers in the networks of RNP's Units and PoPs. The Units, the PoPs with 2Mb access and CAIS were part of the first group (stratum 2); the remaining PoPs belonged to the second group (stratum 3). The current project of implantation of an NTP hierarchy is much more daring. RNP's NTP stratum 1 server is expected to serve as a time reference not only to the PoPs' internal networks and RNP's Support Units, but also to the public in general, obviously based on a defined hierarchy and access policy. 4. Model for RNP's backboneNTP implements a model of synchronization hierarchically distributed. On top, there are the stratum 1 time servers, computers connected directly to high precision devices known as "reference clocks" (or stratum 0 servers). Typically, these devices can be atomic clocks, GPS (Global Positioning Systems) receivers or radio receivers. Any NTP server having as a time reference a stratum 1 server becomes a stratum 2; any NTP server having as a time reference a stratum 2 server becomes a stratum 3, and so on. RNP's NTP stratum 1 server in particular will use GPS technology, which gets the time directly from a group of satellites.
Picture 4.1: Model of NTP Hierarchy in RNP's backbone As picture 4.1 indicates, the proposal is that the NTP hierarchy in RNP's backbone be as follows:
4.1. NTP Servers with which to synchronizeThe proposal consists of:
Obviously, in the process of choosing the servers with which to synchronize, one should consider aspects such as: lower stratum level, precision and physical proximity (to avoid long delays and the generation of unnecessary traffic). Similarly, one should avoid common points of failure and the creation of loops. 4.2. Access PolicyCAIS's proposal is that:
5. Place hosting NTP stratum 1At this point, it is important to consider the following at the time of choosing:
6. NTP Version and Operational System to be used6.1. Which NTP version to use Nowadays, NTPv3 and NTPv4 versions are available. Although the first one is considered the oficial Internet standard , CAIS recommends that the NTP servers be implemented using version 4, for the following reasons: This version incorporates new functionalities and refinements in the algorithms used in version 3, resulting in code reduction and consequently, speed improvement. Moreover, the precision as well as the authentication scheme have been improved. There are NTPv3 and NTPv4 implementations, of public domain, which run in most Unix operational systems , among which: AIX, HP-UX, Irix, Linux, SCO Unix, OSF/1, Solaris, system V.4, FreeBSD. In the NTPv4 implementation in particular, the NTP server for Windows NT systems is included; however, the aforesaid implementation has problems related to: time resolution, support to reference clock drivers, authentication and name resolution. Therefore, CAIS strongly recommends implementing NTP servers in Unix platforms. 7. MonitoringBy creating a program ("spider") which consults the servers of a particular NTP hierarchy, CAIS intends to monitor NTP stratum 2 and 3 servers in RNP's backbone on a regular basis so as to ensure the sanity of the service in terms of quality, reliability and strength. 8. Expected ResultsFrom its Points of Presence, state networks and other authorized networks, RNP intends to organize a stratum 2 hierarchy to be used by the public in general. This hierarchy will distribute the amount of processing, resulting in a stabler and more reliable service to the fnal user. After making this new service known, RNP hopes that in the next two months all its Points of Presence will have implemented their local NTP servers, allowing the subsequent creation of NTP stratum 3 servers in the client networks. |
