Re: [systemd-devel] "Correct" way to obtain DHCP lease info?

2021-04-22 Thread Bruce A. Johnson 

On 22/04/2021 16:14, Bruce A. Johnson wrote:
I'm still trying to get an explanation of why having a valid DHCP 
address is not in itself good enough. 
Correction: I'm still trying to get an explanation from my requirements 
person :facepalm:


Bruce A. Johnson | Firmware Engineer
Blue Ridge Networks, Inc.
14120 Parke Long Court Suite 103 | Chantilly, VA 20151
Main: 1.800.722.1168 | Direct: 703-633-7332
http://www.blueridgenetworks.com
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Re: [systemd-devel] "Correct" way to obtain DHCP lease info?

2021-04-22 Thread Bruce A. Johnson 
I'm still trying to get an explanation of why having a valid DHCP 
address is not in itself good enough. The only reason I've been able to 
see is that after the lease is issued, and before the time comes to 
refresh the lease, there could be a communication failure somewhere 
between the switch the DHCP client is on and the home office where the 
DHCP server is. One would assume that application failures would be a 
reasonable clue Regardless, it seems to me that it's not 
unreasonable for an application outside of systemd-networkd to be able 
to obtain the DHCP lease information. Am I off base here?


Bruce A. Johnson | Firmware Engineer
Blue Ridge Networks, Inc.
14120 Parke Long Court Suite 103 | Chantilly, VA 20151
Main: 1.800.722.1168 | Direct: 703-633-7332
http://www.blueridgenetworks.com
OpenPGP key ID: 296D1CD6F2B84CAB https://keys.openpgp.org/

On 22/04/2021 12:00, Mantas Mikulėnas wrote:
On Thu, Apr 22, 2021 at 6:17 PM Bruce A. Johnson 
> wrote:


Silvio, thanks for the suggestion. I'm not concerned with keeping
the lease forever; the system actually experiences a topology
change as it's switched from one network to another, and I can
catch that from the DBus events that occur. The problem we're
trying to solve is to contact some address that we're sure exists
on the network, without knowing anything about that network. The
default gateway was an obvious choice, but someone wants to cover
the case of there being a private LAN with no gateway. The only
other choice I could see is the DHCP server that issues the lease.

Hmm, don't you also have the case of there being a private LAN with no 
gateway and no DHCP? Or possibly the case of a DHCP relay. And since 
you don't know anything about the network, you also don't know whether 
the address will respond to your communication attempts (other than 
ARP) -- it might be pingable but it might be not.


I'm curious about what brought this problem into existence in the 
first place. Why *is* it necessary to contact a random address within 
the network? (If it's to check that the physical interface is working, 
then just the fact that you somehow acquired a lease would be enough. no?)


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Mantas Mikulėnas


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Re: [systemd-devel] "Correct" way to obtain DHCP lease info?

2021-04-22 Thread Mantas Mikulėnas 
On Thu, Apr 22, 2021 at 6:17 PM Bruce A. Johnson <
bjohn...@blueridgenetworks.com> wrote:

> Silvio, thanks for the suggestion. I'm not concerned with keeping the
> lease forever; the system actually experiences a topology change as it's
> switched from one network to another, and I can catch that from the DBus
> events that occur. The problem we're trying to solve is to contact some
> address that we're sure exists on the network, without knowing anything
> about that network. The default gateway was an obvious choice, but someone
> wants to cover the case of there being a private LAN with no gateway. The
> only other choice I could see is the DHCP server that issues the lease.
>
Hmm, don't you also have the case of there being a private LAN with no
gateway and no DHCP? Or possibly the case of a DHCP relay. And since you
don't know anything about the network, you also don't know whether the
address will respond to your communication attempts (other than ARP) -- it
might be pingable but it might be not.

I'm curious about what brought this problem into existence in the first
place. Why *is* it necessary to contact a random address within the
network? (If it's to check that the physical interface is working, then
just the fact that you somehow acquired a lease would be enough. no?)

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Re: [systemd-devel] "Correct" way to obtain DHCP lease info?

2021-04-22 Thread Bruce A. Johnson 
Silvio, thanks for the suggestion. I'm not concerned with keeping the 
lease forever; the system actually experiences a topology change as it's 
switched from one network to another, and I can catch that from the DBus 
events that occur. The problem we're trying to solve is to contact some 
address that we're sure exists on the network, without knowing anything 
about that network. The default gateway was an obvious choice, but 
someone wants to cover the case of there being a private LAN with no 
gateway. The only other choice I could see is the DHCP server that 
issues the lease.


As my thinking has evolved, I really want to get at more DHCP lease 
information when it comes in, like a private DHCP option code that 
conveys something about the environment. I came across a comment 
somewhere that said the only way is to set the systemd-networkd client 
to use debug log level and read from the journal, but isn't there a more 
direct way, like with the Dbus signals that tell subscribers about 
network interface status?


Bruce A. Johnson | Firmware Engineer
Blue Ridge Networks, Inc.
14120 Parke Long Court Suite 103 | Chantilly, VA 20151
Main: 1.800.722.1168 | Direct: 703-633-7332
http://www.blueridgenetworks.com
OpenPGP key ID: 296D1CD6F2B84CAB https://keys.openpgp.org/

On 21/04/2021 15:34, Silvio Knizek wrote:

Am Mittwoch, dem 21.04.2021 um 14:24 -0400 schrieb Bruce A. Johnson:

Is there a correct way to obtain information about the DHCP lease
received by systemd-networkd's DHCP client functionality? It was easy
enough to find SERVER_ADDRESS in /var/run/systemd/netif/leases/4, but
there is a big fat warning stamped at the top of the file:


# This is private data. Do not parse.

I'd like to be able to make a widget that can tell me which DHCP server
issued my lease, how much more time I have, etc., mainly because I want
to be able to ping something that is known to be on the network. I'm
dealing with a lazy sysadmin who doesn't want to put a gateway on this
private network, I haven't found a solution using the CLI tools.

Thanks in advance.

Hi Bruce,

IMHO "having a lease" is not a good metric to determine if you can
access something.
I would suggest something along this line:

--- /etc/systemd/system/internal-network-accessable.target
[Unit]
Description=Internal System Accessable
---
--- /etc/systemd/system/check-if-internal-system-is-accessable.service
[Unit]
Description=Check if internal system can be reached

[Service]
ExecStart=/usr/local/bin/check-if-internal-system-is-accessable.sh
Restart=always

[Install]
WantedBy=multi-user.target
---
--- /usr/local/bin/check-if-internal-system-is-accessable.sh
#!/usr/bin/bash
while :; do
 if wget -q --spider $INTERNAL_RESOURCE; then
 systemctl start internal-network-accessable.target
 else
 systemctl stop internal-network-accessable.target
 fi
 sleep 600
done
---

Than you can check just the status of the .target. You may need to
tweak the lifeness probe, YMMV.

Also in sd-networkd you can configure a .network to never loose its
lease, see man:systemd.network → KeepConfiguration=

HTH
Silvio

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Re: [systemd-devel] "Correct" way to obtain DHCP lease info?

2021-04-21 Thread Silvio Knizek 
Am Mittwoch, dem 21.04.2021 um 14:24 -0400 schrieb Bruce A. Johnson:
> Is there a correct way to obtain information about the DHCP lease 
> received by systemd-networkd's DHCP client functionality? It was easy 
> enough to find SERVER_ADDRESS in /var/run/systemd/netif/leases/4, but 
> there is a big fat warning stamped at the top of the file:
> 
> > # This is private data. Do not parse.
> I'd like to be able to make a widget that can tell me which DHCP server 
> issued my lease, how much more time I have, etc., mainly because I want 
> to be able to ping something that is known to be on the network. I'm 
> dealing with a lazy sysadmin who doesn't want to put a gateway on this 
> private network, I haven't found a solution using the CLI tools.
> 
> Thanks in advance.
Hi Bruce,

IMHO "having a lease" is not a good metric to determine if you can
access something.
I would suggest something along this line:

--- /etc/systemd/system/internal-network-accessable.target
[Unit]
Description=Internal System Accessable
---
--- /etc/systemd/system/check-if-internal-system-is-accessable.service
[Unit]
Description=Check if internal system can be reached

[Service]
ExecStart=/usr/local/bin/check-if-internal-system-is-accessable.sh
Restart=always

[Install]
WantedBy=multi-user.target
---
--- /usr/local/bin/check-if-internal-system-is-accessable.sh
#!/usr/bin/bash
while :; do
if wget -q --spider $INTERNAL_RESOURCE; then
systemctl start internal-network-accessable.target
else
systemctl stop internal-network-accessable.target
fi
sleep 600
done
---

Than you can check just the status of the .target. You may need to
tweak the lifeness probe, YMMV.

Also in sd-networkd you can configure a .network to never loose its
lease, see man:systemd.network → KeepConfiguration=

HTH
Silvio


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[systemd-devel] "Correct" way to obtain DHCP lease info?

2021-04-21 Thread Bruce A. Johnson 
Is there a correct way to obtain information about the DHCP lease 
received by systemd-networkd's DHCP client functionality? It was easy 
enough to find SERVER_ADDRESS in /var/run/systemd/netif/leases/4, but 
there is a big fat warning stamped at the top of the file:



# This is private data. Do not parse.
I'd like to be able to make a widget that can tell me which DHCP server 
issued my lease, how much more time I have, etc., mainly because I want 
to be able to ping something that is known to be on the network. I'm 
dealing with a lazy sysadmin who doesn't want to put a gateway on this 
private network, I haven't found a solution using the CLI tools.


Thanks in advance.

--
Bruce A. Johnson | Firmware Engineer
Blue Ridge Networks, Inc.
14120 Parke Long Court Suite 103 | Chantilly, VA 20151
Main: 1.800.722.1168 | Direct: 703-633-7332
http://www.blueridgenetworks.com
OpenPGP key ID: 296D1CD6F2B84CAB https://keys.openpgp.org/




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