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30 votes
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What is the use of NTP server when devices have accurate time?

Internal clocks are only so accurate. With an uptime of months or sometimes years, your nodes can drift considerably from correct time. Also, some nodes lack a battery-powered RTC, so they default to ...
Zac67's user avatar
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26 votes

What is the use of NTP server when devices have accurate time?

Your question is based on a number of inaccurate assumptions. First off, not all systems actually have an internal clock. The Raspberry Pi is a trivial example of such a system, but there are many ...
Austin Hemmelgarn's user avatar
13 votes

What is the use of NTP server when devices have accurate time?

A slightly different perspective than the other answers, in the context of information security. We do not really care about how time is precise. What we want to make sure of is that time is the same ...
WoJ's user avatar
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7 votes

What is the use of NTP server when devices have accurate time?

Leap seconds Nobody likes them, but they are a part of UTC, so if you want your clock to be in UTC ( to be able to have the same timestamps as everybody else on the internet uses ) rather than TAI, ...
PlasmaHH's user avatar
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5 votes
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Cisco IOS NTP do not sync time after reboot

You are correct. This is a DNS resolution issue. The ntp process internally uses addresses, not names. So, although you can enter a name, and the system may store the name in the configuration, the ...
Ricky's user avatar
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5 votes
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Will the packet be dropped when the number of hops equals to default TTL?

A TTL of 1 restricts a packet to the local network because a hop to another network will decrement the TTL to 0, then the packet is discarded. Every time a packet is processed, the TTL is supposed to ...
Ron Maupin's user avatar
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5 votes
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Is it bad practice to use a Virtual Router for NTP-Clustering?

I can see a few ways of doing this: Round robin DNS with multiple A records (as suggested in comments by JFL). This would require the clients to properly re-look up the addresses when required, and ...
jonathanjo's user avatar
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4 votes
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Clock Synchronization in a Network

I had a query in Clock Synchronization in a LAN.. If we already have clock synchronization in a network with the help of preamble field in an Ethernet frame. You're confusing clock and time. The ...
vidarlo's user avatar
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4 votes
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Why is accurate time important with networking?

The specific failures you're talking about were likely caused by SSL/TLS certificates which had notBefore or notAfter dates. These determine the time-span during which the cert is valid. If your ...
Jeff Wheeler's user avatar
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4 votes

What is the use of NTP server when devices have accurate time?

If your device has an internal atomic clock, naturally you don't need it NTP servers derive their times from atomic clocks, which are accurate to 1 second in 300 million years. Most devices take their ...
Graham's user avatar
  • 141
3 votes

Cisco swtich stacked NTP configure

You configure a stack as a single switch, not two separate switches. Simply log into the stack and configure NTP: ntp server ip-address [version number] [key key-id] [source interface-type ...
Ron Maupin's user avatar
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3 votes
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Simple NTP question

Looks like you are missing ntp server SERVERNAME If your switch isn't synchronised, it won't allow downstream clients to synchronise either. Check with show ntp status You can use public servers ...
jonathanjo's user avatar
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3 votes
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Cisco ACL for NTP

Solved: permit udp object-group NTP eq ntp any
Satish's user avatar
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3 votes

Cisco Switch - Why do I need to do time synchronization for them

Your network devices (routers, switches, etc.) should be using NTP to keep their times synchronized. The primary benefit is for the logs and troubleshooting. When you look in the logs on your syslog ...
Ron Maupin's user avatar
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3 votes
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NTP architecture questions

Unless you have a very good NTP source, you should set up your NTP servers as clients of low-stratum NTP servers elsewhere (e.g. Internet). You can, and probably should, use multiple, external servers ...
Ron Maupin's user avatar
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3 votes
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IOS does not respond to NTP queries unless client is in "peer" ACL

After doing a "sidegrade" from 15.2M to 12.2SRE on the router, the following configuration now works: access-list 80 permit <UP.STREAM.NTP.SERVER> log access-list 81 permit <MY.CLIENT....
tlund's user avatar
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3 votes
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How does NTP synchronisation work?

The travelling time (delay) is estimated to be half of "the total delay minus remote processing time", assuming symmetrical delays. The processing time is the difference between "...
Ricky's user avatar
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2 votes

How stable are clocks in network equipment

Clocks of network devices usually DO NOT have high-quality oscillators. Because those oscillators are expensive hardware. If all you need is to distribute wall clock time through NTP (with ...
Everton's user avatar
  • 1,636
2 votes

How stable are clocks in network equipment

I have no clue about the internal clock stability, but it doesn't matter much since you absolutely want those devices to be be synchronized, i.e. be NTP clients of a trusted source. This is the only ...
JFL's user avatar
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2 votes

Access rule that permits NTP response

You can make a reflexive ACL, which will allow the response packet to go through. permit udp hosta hostb eq <port> reflect
Rutvij Jethwa's user avatar
2 votes
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Access rule that permits NTP response

If it's an inbound ACL then it's all right. But if you have applied same list to outbound traffic to interface, then it will result in dropping NTP responses back to your host. Your outbound ACL ...
Andrey Prokhorov's user avatar
2 votes

Cisco NTP server does not respond to queries

Stumbled across this old thread as a "related post" to something I was viewing. Windows Servers' (S)NTP client needs to be configured to run in "client mode" when querying Cisco IOS (and probably ...
Marc 'netztier' Luethi's user avatar
2 votes
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MD5 Authentication Character Length

You have it backwards. NTP servers cannot force a client to use authentication. It is the client that demands authentication from the server. The server is happy to serve up NTP to any client that ...
Ron Maupin's user avatar
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2 votes
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How does Peer-to-Peer NTP resolve time variance?

Since neither peer is an authority, they will both adjust their clocks to the midpoint of the difference between them.
Ron Trunk's user avatar
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2 votes

Juniper MX: NTP broadcast on two VRFs with the same addressing

I know that most of the type the same configuration you want in the default instance exists in the same config stanza within routing-instances, in this case it's the other way around. Addressing ...
Jordan Head's user avatar
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2 votes
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NTP Sync issues between Palo Alto 3260 and Juniper MX10003

This was resolved after modifying the format of the authentication key in the Juniper router. We had to enter the key a specific way. For example, if the key was ...
Ben's user avatar
  • 157
2 votes

Why is accurate time important with networking?

So my question is, do certificates require machines to be in sync and what are the implications of machines not being in sync (are there security vulnerabilities). Yes, of course the time needs ...
Ron Maupin's user avatar
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2 votes

Query on PTP Transparent Clock

PTP with Transparent Clock is used to synchronize the clock of a network client with a server (similar to NTP). However, PTP is mainly used in LANs, with much higher precision than NTP (usually 10'...
Bobby Voychin's user avatar
2 votes
Accepted

How important is it for time to be synchronized between adjacent OSPF neighbors?

OSPF doesn't exchange timestamps, so offset time between routers shouldn't be an issue. MD5 authentication doesn't rely on synchronized time either. Without more details on your config, device time ...
Zac67's user avatar
  • 83.9k
2 votes

What is the use of NTP server when devices have accurate time?

NTP server can set the correct/exact time to more than one device. This is very important when you are working with systems that depend on the correct time. If there is an internal clock it also needs ...
KWriter's user avatar
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