Configuring NTP Access Restrictions You can control access to NTP services by using access groups. Specifically, you can specify the types of requests that the Cisco CG-OS router allows and the servers from which it accepts responses.
Full Answer
What is NTP server mode in Cisco router?
NTP Server Mode. In this mode, Router reads time from NTP Source. Unless we manually define the NTP source, router uses its own clock as NTP source. As per requirement, we can configure router’s clock or can use an external clock as NTP source. Once NTP Source is configured, NTP Server router advertises this time in network.
How do I control access to NTP services?
You can control access to NTP services by using access groups. Specifically, you can specify the types of requests that the device allows and the servers from which it accepts responses. If you do not configure any access groups, NTP access is granted to all devices.
What happens if no NTP Access Group is specified?
If no access groups are specified, all access types are granted to all devices. If any access groups are specified, only the specified access types are granted. To remove access control to the switch NTP services, use the no ntp access-group {query-only | serve-only | serve | peer} global configuration command.
What is the default restriction in ntpd?
The default restriction tells ntpd how to handle packets from hosts (including remote time servers) and subnets that do not otherwise have a specific restriction. Choosing the correct default restriction can simplify your ntpd configuration while providing the security you need.
How do I configure NTP to restrict remote access?
To configure NTP access restrictions for a specific address: From configuration mode, access the configuration statement that restricts NTP access for a specific address. user@host# set system ntp restrict address address ; Specify the subnet mask of the host.
What are NTP control queries?
NTP communication consists of time requests and control queries. Time requests provide the standard client/server relationship in which a client requests time synchronization from an NTP server. Control queries provide ways for remote systems to get configuration information and reconfigure NTP servers.
How do I restrict restrict NTP mode 6 queries?
Add the following lines to the /etc/ntp. conf file. This disables mode 6 and 7 queries, as well as other vulnerabilities, for all IP addresses, but allows them on the local loopback interface. Add restrict and server entries for each trusted NTP server on the network.
How do I configure my Cisco router as an NTP server?
To deploy a router as NTP server, following steps are required.Adjust router clock.Configure Loop back interface.Add loopback interface's network in routing table.Configure NTP Server.Configure active interfaces to act as NTP Server only.
What are NTP mode 6 queries?
“Mode 6” commands allow NTP to be reconfigured while it is running. NTP requests can be used to mount a Denial of Service attack, when an attacker tries to overwhelm a victim's server by flooding it with requests.
What does NTP master command do?
Description. This command configures the router as the master NTP server from which other NTP peers can receive their NTP time. (See the ntp peer command for setting peer values.)
How do I know if I have NTP mode 6?
Methodology. If you would like to test your own device to see if it supports Mode 6 queries, try the command: "ntpq -c rv [IP]".
What is NTP protocol?
Network Time Protocol (NTP) is an internet protocol used to synchronize with computer clock time sources in a network. It belongs to and is one of the oldest parts of the TCP/IP suite.
Is NTP a UDP?
NTP is a built-on UDP, where port 123 is used for NTP server communication and NTP clients use port 1023 (for example, a desktop). Unfortunately, like many legacy protocols, NTP suffers from security issues.
Can a Cisco switch be an NTP server?
Cisco devices can serve as NTP servers, also known as NTP Masters. An NTP Master can utilize either an upstream NTP clock or it's own internal hardware clock – which may be useful if you're working in a lab setting not connected to the internet.
Which command will configure Cisco device as authoritative NTP server?
Use the ntp master command in global configuration mode if you want the system to be an authoritative NTP server, even if the system is not synchronized to an outside time source.
Which two tasks must be performed to configure NTP?
Step 1: Configure an authentication key pair for NTP and specify whether the key will be trusted or untrusted. Step 2: Set the IP address of the NTP server and the public key. Step 3: Enable NTP client mode.
How do you query a time server?
To verify the NTP server list:Click on the Windows button.In the "Search programs and files" box, type cmd and press Enter.If necessary, select cmd from the list of search results.In the command prompt window, enter w32tm /query /peers.Check that an entry is shown for each of the servers listed above.
How do I test NTP mode 6 queries?
Methodology. If you would like to test your own device to see if it supports Mode 6 queries, try the command: "ntpq -c rv [IP]".
What is NTP protocol?
Network Time Protocol (NTP) is an internet protocol used to synchronize with computer clock time sources in a network. It belongs to and is one of the oldest parts of the TCP/IP suite.
How do I know if NTP is synchronized?
The ntpstat command will report the synchronisation state of the NTP daemon running on the local machine....exit status of ntpstat commandIf exit status 0 – Clock is synchronised.exit status 1 – Clock is not synchronised.exit status 2 – If clock state is indeterminant, for example if ntpd is not contactable.
What is NTP in Cisco?
NTP as a Time Server. The Cisco NX-OS device can use NTP to distribute time. Other devices can configure it as a time server. You can also configure the device to act as an authoritative NTP server, enabling it to distribute time even when it is not synchronized to an outside time source.
How to control NTP?
You can control access to NTP services by using access groups. Specifically, you can specify the types of requests that the device allows and the servers from which it accepts responses.
What is NTP in a network?
In a broadcast-based NTP association, an NTP server sends NTP broadcast packets throughout a network. Broadcast clients listen for the NTP broadcast packets sent by the server and do not engage in any polling.
Why enable CFS distribution for NTP?
You can enable CFS distribution for NTP in order to distribute the NTP configuration to other CFS-enabled devices.
Why configure NTP peers?
You can configure NTP peers to provide redundancy in case an NTP server fails.
What is NTP association?
An NTP association can be one of the following: A peer association—The device can either synchronize to another device or allow another device to synchronize to it. A server association—The device synchronizes to a server. You need to configure only one end of an association.
What is the NTP protocol?
The Network Time Protocol (NTP) synchronizes the time of day among a set of distributed time servers and clients so that you can correlate events when you receive system logs and other time-specific events from multiple network devices. NTP uses the User Datagram Protocol (UDP) as its transport protocol. All NTP communications use Coordinated Universal Time (UTC).
What is NTP in Cisco?
NTP as a Time Server. The Cisco NX-OS device can use NTP to distribute time. Other devices can configure it as a time server. You can also configure the device to act as an authoritative NTP server, enabling it to distribute time even when it is not synchronized to an outside time source.
How to control NTP?
You can control access to NTP services by using access groups. Specifically, you can specify the types of requests that the device allows and the servers from which it accepts responses.
What is NTP association?
An NTP association can be one of the following: A peer association—The device can either synchronize to another device or allow another device to synchronize to it. A server association—The device synchronizes to a server. You need to configure only one end of an association.
Why configure NTP peers?
You can configure NTP peers to provide redundancy in case an NTP server fails.
What is a stratum in NTP?
NTP uses a stratum to describe the distance between a network device and an authoritative time source: A stratum 1 time server is directly attached to an authoritative time source (such as a radio or atomic clock or a GPS time source).
How efficient is NTP?
NTP is extremely efficient; no more than one packet per minute is necessary to synchronize two machines to within a millisecond of each other.
What is NTP protocol?
About NTP. The Network Time Protocol (NTP) synchronizes the time of day among a set of distributed time servers and clients so that you can correlate events when you receive system logs and other time-specific events from multiple network devices. NTP uses the User Datagram Protocol (UDP) as its transport protocol.
How many levels can you control NTP access?
You can control NTP access on two levels as described in these sections:
What is peer in NTP?
1. peer—Allows time requests and NTP control queries and allows the switch to synchronize itself to a device whose address passes the access list criteria.
What happens if the source IP address matches the access lists for more than one access type?
If the source IP address matches the access lists for more than one access type, the first type is granted. If no access groups are specified, all access types are granted to all devices. If any access groups are specified, only the specified access types are granted.
Is NTP enabled on all interfaces?
NTP services are enabled on all interfaces by default.
How many commands does NTP server take?
NTP server configuration is straightforward. It takes only two commands to deploy a router as NTP Server.
Which command configures active interface to listen to NTP broadcast message only?
As explained earlier, first command insists router to use NTP server time instead of its own local time and second command configures active interface to listen NTP broadcast message only.
What is the best NTP scale?
Stratum defines the reliability and accuracy of NTP source. It uses a scale of stratum 0 to stratum 15 for NTP sources. In this scale, stratum 0 is the most reliable and stratum 15 is the worst reliable source of time. Stratum-0 devices use the atomic clock and provide the most accurate time.
How many modes does a Cisco router have?
A Cisco router can be configured in three modes: -
How many interfaces are there in R1?
We have two active interfaces in router R1. Let’s configure them to only broadcast the NTP messages.
What is a public time server?
Public Time Servers stand next in this scale and are generally referred as stratum-1 devices. These servers sync their clock with stratum-0 devices and provide an optimized time for regular devices. To use this optimized time, devices do not need any additional CPU power or memories. Any regular device can use this time. We can configure any Cisco router to use this time.
Which NTP is the worst?
Stratum 1-15 are valid levels and used in Cisco router. 1 is the most reliable and 15 is the worst (but still valid) NTP source.
Do you need IP addresses for restrict statements?
You must use IP addresses on restrict statements.
Can you use IP address on server?
You may use either a hostname or IP address on the server line. You must use an IP address on the restrict line. There is no harm in adding the restrictions shown in brackets but keep in mind that if you are accepting time from someone it may be considered courteous to allow them to see a bit of information about their client.
