Hi there,

I read the documentation a few times but can not find if it's possible
to specify IP address for outgoing connections?

I have server with multiple IP addresses and I need to specify the
concrete one to be used to sync with servers/peers. For now, ntpd
selects one of the listening interfaces (still the same one, but I can
not determine why this one).

Thanks,
Blažej
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In comp.protocols.time.ntp, you wrote:
> Hi there,
>
> I read the documentation a few times but can not find if it's possible
> to specify IP address for outgoing connections?
>
> I have server with multiple IP addresses and I need to specify the
> concrete one to be used to sync with servers/peers. For now, ntpd
> selects one of the listening interfaces (still the same one, but I can
> not determine why this one).

Does not route -n
tell you which one? Remember it always used the most the specific
interface.
Ie, if you have say 0.0.0.0/0 and 128.0.0.0/8 on different interfaces,and your address of your
ntp server is 128.113.27.6 then it will use the second. If you have
128.113.27.0/24 on a third interface, it will use that third one. If
there are two of equal depth covering the interface, then it will use
the last on I believe.

Ie, with a specific set of routes, it should always pick the same
interface. The server uses the same address it received the query on, so
it will depend on the incoming routing of the response.
>
>
> Thanks,
> Blažej
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Well, my server has dummy interface and multiple /32 IP addresses.
They are announced via OSPF to IGP.

The idea is to anycast 2 IPs (HA solution) and when primary server
goes down, secondary will response to primary's IP address also.

Primary server has the following config:
interface ignore wildcard
interface listen 172.20.1.3
interface listen 172.20.2.3
interface listen 172.20.1.19

+ FRR: ip ospf cost 700 172.20.2.3

Secondary:
interface ignore wildcard
interface listen 172.20.1.3
interface listen 172.20.2.3
interface listen 172.20.2.19

+ FRR: ip ospf cost 700 172.20.1.3

The IPs 172.20.1.3 and 172.20.2.3 are "floating IPs". And I need from
ntpd to make outgoing connections from 172.20.1.19 and 172.20.2.19
respectively.

I did tests and now, ntpd is selecting "172.20.2.3" for outgoing
"connections" from primary server. And it fails, because 172.20.2.3 is
routed to secondary (server will never get the response).

št 29. 9. 2022 o 15:18 William Unruh <unruh@physics.ubc.ca> napísal(a):
>
> In comp.protocols.time.ntp, you wrote:
> > Hi there,
> >
> > I read the documentation a few times but can not find if it's possible
> > to specify IP address for outgoing connections?
> >
> > I have server with multiple IP addresses and I need to specify the
> > concrete one to be used to sync with servers/peers. For now, ntpd
> > selects one of the listening interfaces (still the same one, but I can
> > not determine why this one).
>
> Does not route -n
> tell you which one? Remember it always used the most the specific
> interface.
> Ie, if you have say 0.0.0.0/0 and 128.0.0.0/8 on different interfaces,and your address of your
> ntp server is 128.113.27.6 then it will use the second. If you have
> 128.113.27.0/24 on a third interface, it will use that third one. If
> there are two of equal depth covering the interface, then it will use
> the last on I believe.
>
> Ie, with a specific set of routes, it should always pick the same
> interface. The server uses the same address it received the query on, so
> it will depend on the incoming routing of the response.
> >
> >
> > Thanks,
> > Blažej
> > --
> > This is questions@lists.ntp.org
> > Subscribe: questions+subscribe@lists.ntp.org
> > Unsubscribe: questions+unsubscribe@lists.ntp.org
> >
> >
> >
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On 2022-09-29, Blažej Krajňák <blazej.krajnak@gmail.com> wrote:
> Well, my server has dummy interface and multiple /32 IP addresses.
> They are announced via OSPF to IGP.
>
> The idea is to anycast 2 IPs (HA solution) and when primary server
> goes down, secondary will response to primary's IP address also.
>
> Primary server has the following config:
> interface ignore wildcard
> interface listen 172.20.1.3
> interface listen 172.20.2.3
> interface listen 172.20.1.19
>
> + FRR: ip ospf cost 700 172.20.2.3
>
> Secondary:
> interface ignore wildcard
> interface listen 172.20.1.3
> interface listen 172.20.2.3
> interface listen 172.20.2.19
>
> + FRR: ip ospf cost 700 172.20.1.3
>
> The IPs 172.20.1.3 and 172.20.2.3 are "floating IPs". And I need from
> ntpd to make outgoing connections from 172.20.1.19 and 172.20.2.19
> respectively.
>
> I did tests and now, ntpd is selecting "172.20.2.3" for outgoing
> "connections" from primary server. And it fails, because 172.20.2.3 is
> routed to secondary (server will never get the response).

It would probably also help if you told us which operating system you
are using.

It sounds like you have both interfaces linked to 0.0.0.0, in which case
it is the second one ( the latest one) that will be used as the one for
sending out the ntp packets. As you notice, the incoming packets and the
outgoing ones need to use the same IP.
I have no idea what a "floating IP" is, And I have no idea what
" I need from
ntpd to make outgoing connections from 172.20.1.19 and 172.20.2.19
respectively.
"
means. And ntpd outgoing connection goes out one interface and has one
IP addresses as its source address. And it chooses which IP to use
deterministically.

>
> št 29. 9. 2022 o 15:18 William Unruh <unruh@physics.ubc.ca> napísal(a):
>>
>> In comp.protocols.time.ntp, you wrote:
>> > Hi there,
>> >
>> > I read the documentation a few times but can not find if it's possible
>> > to specify IP address for outgoing connections?
>> >
>> > I have server with multiple IP addresses and I need to specify the
>> > concrete one to be used to sync with servers/peers. For now, ntpd
>> > selects one of the listening interfaces (still the same one, but I can
>> > not determine why this one).
>>
>> Does not route -n
>> tell you which one? Remember it always used the most the specific
>> interface.
>> Ie, if you have say 0.0.0.0/0 and 128.0.0.0/8 on different interfaces,and your address of your
>> ntp server is 128.113.27.6 then it will use the second. If you have
>> 128.113.27.0/24 on a third interface, it will use that third one. If
>> there are two of equal depth covering the interface, then it will use
>> the last on I believe.
>>
>> Ie, with a specific set of routes, it should always pick the same
>> interface. The server uses the same address it received the query on, so
>> it will depend on the incoming routing of the response.
>> >
>> >
>> > Thanks,
>> > Blažej
>> > --
>> > This is questions@lists.ntp.org
>> > Subscribe: questions+subscribe@lists.ntp.org
>> > Unsubscribe: questions+unsubscribe@lists.ntp.org
>> >
>> >
>> >
>> --
>> This is questions@lists.ntp.org
>> Subscribe: questions+subscribe@lists.ntp.org
>> Unsubscribe: questions+unsubscribe@lists.ntp.org
>>
>>
>>

I would of expected the routing table to be used to determine which
interface IP address interface  to use to send to the specified NTP
server address so its not really a NTP server setup

Ross Wilson

On 29/09/2022 5:33 pm, Blažej Krajňák wrote:
> Hi there,
>
> I read the documentation a few times but can not find if it's possible
> to specify IP address for outgoing connections?
>
> I have server with multiple IP addresses and I need to specify the
> concrete one to be used to sync with servers/peers. For now, ntpd
> selects one of the listening interfaces (still the same one, but I can
> not determine why this one).
>
>
> Thanks,
> Blažej
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