hello folks, So DHCP can also be used to set NTP servers on clients, for both IPv4[rfc2132] and IPv6[rfc5908]. I'm looking for statistics on setting NTP servers on clients using DHCP, in the wild. Does anyone know if there is any available somewhere? I'm also looking for reports from operators and their experiences on this, and why they use (or not) this DHCP feature, and what types of networks is this deployed, and their motivations, etc. Thanks in advance, /giovane
Hi Giovane On Fri, Oct 01, 2021 at 04:12:15PM +0200, Giovane C. M. Moura via NANOG wrote:
hello folks,
So DHCP can also be used to set NTP servers on clients, for both IPv4[rfc2132] and IPv6[rfc5908].
I'm looking for statistics on setting NTP servers on clients using DHCP, in the wild. Does anyone know if there is any available somewhere?
I'm also looking for reports from operators and their experiences on this, and why they use (or not) this DHCP feature, and what types of networks is this deployed, and their motivations, etc.
Some PC OSs such as Linux distributions obey the "ntp-servers" ISC DHCP option (mapped to option code 42 in RFC 2132 section 8.3) and configure the client's NTP service with it. But not all DHCP clients do. E.g., Android phones ignore this option completely. We use this option in our office to configure a local timeserver (uses a Garmin GPS 18x LVC receiver), but it only works on client machines that attempt to make use of that option. Mukund
Giovane, While Murkund’s point about some devices ignoring this option (I’m not sure why any cellphones would accept it, for example, Android or otherwise, since they get time from the cellular network), it’s pretty much an industry standard that desktop and WiFi *VoIP* phones all use it. It’s how they get the time to display on their little screens :) Other than that major device segment, though, I’ve only seen other devices support direct hard-coded configuration of an NTP server. Windows is certainly that way, and even has a way to distribute time from the ubiquitous Windows server. I think hard coding is still the defacto standard for everything other then VoIP. -mel
On Oct 1, 2021, at 8:08 AM, Mukund Sivaraman <muks@mukund.org> wrote:
Hi Giovane
On Fri, Oct 01, 2021 at 04:12:15PM +0200, Giovane C. M. Moura via NANOG wrote: hello folks,
So DHCP can also be used to set NTP servers on clients, for both IPv4[rfc2132] and IPv6[rfc5908].
I'm looking for statistics on setting NTP servers on clients using DHCP, in the wild. Does anyone know if there is any available somewhere?
I'm also looking for reports from operators and their experiences on this, and why they use (or not) this DHCP feature, and what types of networks is this deployed, and their motivations, etc.
Some PC OSs such as Linux distributions obey the "ntp-servers" ISC DHCP option (mapped to option code 42 in RFC 2132 section 8.3) and configure the client's NTP service with it.
But not all DHCP clients do. E.g., Android phones ignore this option completely.
We use this option in our office to configure a local timeserver (uses a Garmin GPS 18x LVC receiver), but it only works on client machines that attempt to make use of that option.
Mukund
Thanks everyone for their answers. To summarize: 1. NTP from DHCP usage: * Not all clients accept DHCP configs for NTP (like android phones) * WiFi VoIP phones use ntp from dhcp (default) -- Google Fiber case showed that VOIP phones may fail to register if DHCP provides unreachable NTP servers. 2. DOCSIS devices use TIME protocol, and sometimes NTP as well 3. Most devices likely to use hard-coded values I'm approaching this a researcher, trying to understand these settings usage in the wild. W.r.t. Hal Murray bursts queries, that's interesting, we also run some servers that we share on the NTPPool but we don't see such bursts -- we see sort of a stable timeseries with thousands of NTP queries per second. thanks everyone for sharing their thoughts and experiences, /giovane On 10/1/21 5:05 PM, Mukund Sivaraman wrote:
Hi Giovane
On Fri, Oct 01, 2021 at 04:12:15PM +0200, Giovane C. M. Moura via NANOG wrote:
hello folks,
So DHCP can also be used to set NTP servers on clients, for both IPv4[rfc2132] and IPv6[rfc5908].
I'm looking for statistics on setting NTP servers on clients using DHCP, in the wild. Does anyone know if there is any available somewhere?
I'm also looking for reports from operators and their experiences on this, and why they use (or not) this DHCP feature, and what types of networks is this deployed, and their motivations, etc.
Some PC OSs such as Linux distributions obey the "ntp-servers" ISC DHCP option (mapped to option code 42 in RFC 2132 section 8.3) and configure the client's NTP service with it.
But not all DHCP clients do. E.g., Android phones ignore this option completely.
We use this option in our office to configure a local timeserver (uses a Garmin GPS 18x LVC receiver), but it only works on client machines that attempt to make use of that option.
Mukund
Hi Giovane, a time server is a required DHCP option for DOCSIS devices. This uses the older TIME protocol (UDP port 37, RFC 868). However, it's common for DOCSIS devices like MTAs, STBs, etc to also request and use NTP server addresses received via DHCP (they may apply this using SNTP rather than a fully fledged NTP client). As one data point, Google Fiber (a large GPON based ISP in USA) provides NTP servers to customers via DHCP. We actually had to contact them as they were providing a set of server addresses where one or more of the servers was no longer reachable. Some of our VoIP telephones used by employees did not like receiving bad info and would intermittently fail to register. Google Fiber was able to remove the bad info from their DHCP replies. We've seen some similar behavior in other networks so now I believe we prefer to ignore/override the DHCP provided NTP info with known good server addresses (it seems too common for NTP to simply be ignored/overlooked by network operators and users). --Blake On 10/1/2021 9:12 AM, Giovane C. M. Moura via NANOG wrote:
hello folks,
So DHCP can also be used to set NTP servers on clients, for both IPv4[rfc2132] and IPv6[rfc5908].
I'm looking for statistics on setting NTP servers on clients using DHCP, in the wild. Does anyone know if there is any available somewhere?
I'm also looking for reports from operators and their experiences on this, and why they use (or not) this DHCP feature, and what types of networks is this deployed, and their motivations, etc.
Thanks in advance,
/giovane
participants (4)
-
Blake Hudson -
Giovane C. M. Moura -
Mel Beckman -
Mukund Sivaraman