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ITIS 3110 IT Infrastructure II

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Presentation on theme: "ITIS 3110 IT Infrastructure II"— Presentation transcript:

1 ITIS 3110 IT Infrastructure II
Tony Kombol


3 "Does Anybody Realy Know What Time It Is?"*
Time keeping is one of most fundamental aspects of computer infrastructure Many protocols rely on accurate clocks Correlating information from multiple systems impossible with out a shared clock *Does Anybody Realy Care (CTA aka Chicago, 1969)

4 Time Sources

5 Side note: Difference between precision and accuracy
Closeness to the actual value E.g. the clock is 1 hour off Precision How much it does not vary E.g. the clock varies by less than a nanosecond in a year So which is better? A clock might not vary by more than a nanosecond, but be off by one hour A clock might be off by one second, but vary by a millisecond over the day

6 Network Time Protocol (NTP)
Port 123/udp Can maintain time in fractions of a second Can use external time source e.g. Atomic clock or GPS clock Most computers and devices act as a client

7 Network Time Protocol (NTP)
All servers belong to a ‘Stratum’ Denotes how far from a time source they are Prevents Loops Can only sync with servers in same stratum or higher Stratum 0: time source Stratum 1: server directly attached to time source Etc… Versions available for: UNIX family Windows family SNTP for 2000 and XP Full NTP for Server 2003 and Vista

8 Security concerns Only a few security problems have been identified in the reference implementation of the NTP codebase in its 25+ year history The protocol has been undergoing revision and review over its entire history As of January 2011, there are no security revisions in the NTP specification and no reports at CERT The current codebase for the reference implementation has been undergoing security audits from several sources for several years now There are no known high-risk vulnerabilities in the current released software

9 NTP: Security Considerations
Default configuration is usually client-only Supports authentication if working in a paranoid environment

10 NTP Stratum Yellow arrows are direct connections
Red arrows are network connections

11 Clock strata NTP uses a hierarchical, semi-layered system of levels of clock sources Each level of this hierarchy is termed a stratum Assigned a layer number starting with 0 (zero) at the top The stratum level defines its distance from the reference clock and exists to prevent cyclical dependencies in the hierarchy Note 1: the stratum level is not a guarantee of quality or reliability It is common to find stratum 3 time sources that are higher quality than other stratum 2 time sources Note2: This definition of stratum is also different from the notion of clock strata used in telecommunication systems

12 Clock strata Stratum 0 Stratum 1 Devices such as
Atomic clocks (cesium, rubidium) GPS clocks Radio clocks (e.g. WWV) Stratum-0 devices are traditionally not attached to the network Instead they are locally connected to computers e.g., via an RS-232 connection using a pulse per second signal Stratum 1 These are computers attached to Stratum 0 devices. Normally they act as servers for timing requests from Stratum 2 servers via NTP These computers are also referred to as time servers They are typically attached to the network

13 Clock strata Stratum 2 Computers that send NTP requests to Stratum 1 servers Normally a Stratum 2 computer will reference a number of Stratum 1 servers and use the NTP algorithm to gather the best data sample Dropping any Stratum 1 servers that seem obviously wrong Stratum 2 computers will peer with other Stratum 2 computers to provide more stable and robust time for all devices in the peer group Stratum 2 computers normally act as servers for Stratum 3 NTP requests Stratum 3 These computers employ exactly the same algorithms for peering and data sampling as Stratum 2 Can themselves act as servers for stratum 4 computers, and so on…

14 Clock strata NTP supports up to 256 strata
Only the first 16 are employed Any device at Stratum 16 is considered to be unsynchronized Some systems may reject a time update from a "too highly numbered" stratum Note: Depends on what version of NTP protocol in use

15 SNTP - Simple Network Time Protocol
A less complex implementation of NTP Uses the same protocol Does not require the storage of state over extended periods of time Used in some embedded devices and in applications where high accuracy timing is not required See RFC 1361, RFC 1769, RFC 2030, RFC 4330 and RFC 5905

16 NTP timestamps 64-bit timestamps used by NTP consist of Gives NTP:
32-bit part for seconds 32-bit part for fractional second Gives NTP: Time scale that rolls over every 232 seconds ~136 years Theoretical resolution of 2−32 seconds ~233 picoseconds NTP uses an epoch of January 1, 1900 First rollover occurs in 2036 Before the UNIX year 2038 problem

17 NTP timestamps Implementations should disambiguate NTP time using a knowledge of the approximate time from other sources NTP only works with the differences between timestamps and never their absolute values Wraparound is invisible as long as the timestamps are within 68 years of each other This means that the rollover will be invisible for most running systems, since they will have the correct time to within a very small tolerance However, systems that are starting up need to know the date within no more than 68 years Given the large allowed error, it is not expected that this is too onerous a requirement One suggested method is to set the clock to no earlier than the system build date Many systems use a battery powered hardware clock to avoid this problem

18 NTP timestamps Even so, future versions of NTP may extend the time representation to 128 bits: 64 bits for the second and 64 bits for the fractional- second The current NTP4 format has support for Era Number and Era Offset, that when used properly should aid fixing date rollover issues According to Mills: "The 64 bit value for the fraction is enough to resolve the amount of time it takes a photon to pass an electron at the speed of light. The 64 bit second value is enough to provide unambiguous time representation until the universe goes dim."

19 Stratum 0 clocks are usually directly connected to the network
True False

20 Logging

21 Logging Best practice is to centralize all logs to a dedicated log host Good for debugging, forensics, etc. Centralized logging needs a shared clock for best results

22 Clock synchronization algorithm
To synchronize its clock with a remote server, the NTP client must compute the round-trip delay time and the offset Round-trip delay is d = (t3-t0) – (t2-t1) Where: t0 is the time of the request packet transmission t1 is the time of the request packet reception t2 is the time of the response packet transmission t3 is the time of the response packet reception (t3-t0) is the time elapsed on the client side between the emission of the request packet and the reception of the response packet while t2-t1 is the time the server waited before sending the answer. Offset is given by o = ((t1-t0) + (t2-t3)) /2

23 Clock synchronization algorithm
The NTP synchronization is correct when both the incoming and outgoing routes between the client and the server have symmetrical nominal delay If the routes do not have a common nominal delay, the synchronization has a systematic bias of half the difference between the forward and backward travel times

24 Syslog Port 514/UDP Modern implementations support TCP as well Most computers and devices can generate syslog messages UDP is used because it is stateless

25 Syslog Facilities Every syslog message is associated with a facility
The facility is the general source of the message Example facilities are AUTH CRON DAEMON FTP MAIL Allows different facilities to be handled differently

26 Facility Levels 0-11 Facility Number Keyword Facility Description kern
kern kernel messages 1 user user-level messages 2 mail mail system 3 daemon system daemons 4 auth security/authorization messages 5 syslog messages generated internally by syslogd 6 lpr line printer subsystem 7 news network news subsystem 8 uucp UUCP subsystem 9 clock daemon 10 authpriv 11 ftp FTP daemon

27 Facility Levels (12-23) Facility Number Keyword Facility Description
NTP subsystem 13 log audit 14 log alert 15 cron clock daemon 16 local0 local use 0 (local0) 17 local1 local use 1 (local1) 18 local2 local use 2 (local2) 19 local3 local use 3 (local3) 20 local4 local use 4 (local4) 21 local5 local use 5 (local5) 22 local6 local use 6 (local6) 23 local7 local use 7 (local7)

28 Syslog Priorities Every syslog message has a set priority
Declares how important the message is Examples are: debug notice warning error

29 Severity Levels Code Severity Keyword Description General Description Emergency emerg (panic) System is unusable. A "panic" condition usually affecting multiple apps/servers/sites. At this level it would usually notify all tech staff on call. 1 Alert alert Action must be taken immediately. Should be corrected immediately, therefore notify staff who can fix the problem. An example would be the loss of a primary ISP connection. 2 Critical crit Critical conditions. Should be corrected immediately, but indicates failure in a primary system, an example is a loss of a backup ISP connection. 3 Error err (error) Error conditions. Non-urgent failures, these should be relayed to developers or admins; each item must be resolved within a given time. 4 Warning warning (warn) Warning conditions. Warning messages, not an error, but indication that an error will occur if action is not taken, e.g. file system 85% full - each item must be resolved within a given time. 5 Notice notice Normal but significant condition. Events that are unusual but not error conditions - might be summarized in an to developers or admins to spot potential problems - no immediate action required. 6 Informational info Informational messages. Normal operational messages - may be harvested for reporting, measuring throughput, etc. - no action required. 7 Debug debug Debug-level messages. Info useful to developers for debugging the application, not useful during operations. A common mnemonic used to remember the syslog levels down to top is: "Do I Notice When Evenings Come Around Early".

30 Syslog Configuration Messages can be routed based on facility and priority What subsystem and its importance Destination can be: Local log file Remote syslog server Log files can be written synchronously or asynchronously Synchronous – slower but guaranteed write Asynchronous – faster, but may lose some logs if the system crashes

31 Example Syslog Configuration
# Log all kernel messages to the console. # Logging much else clutters up the screen. kern.* /dev/console # Log anything (except mail) of level info or higher. # Don't log private authentication messages! *.info;mail.none;authpriv.none;cron.none /var/log/messages # Send all logs to

32 Notes about the configuration
* The asterisk is a ‘glob’ character. It means to match anything You will see it in many configuration files as well as on the command line /dev/console UNIX has a philosophy that everything is a file /dev/console is a device file It writes messages to all locally attached terminals

33 Syslog: Security Considerations
No authentication No encryption UDP source can be spoofed Malicious user could run log server out of disk space Same for a mis-configured system

34 Syslog: Security Mitigations
Limit access to Syslog using firewall Run on internal network if possible Log to a separate partition Monitor disk usage on log server Use more feature-rich syslog implementations that support TCP and/or encryption

35 Why do NTP and Syslog need to work together:
Both share the same base protocol All systems need a common timebase for log timestamps TCP requires synchronized packet transfers It keeps the NSA synchronized

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