Questions[dhcpd](ubuntu)

When I connect a USB-to-Ethernet adapter (that has been previously used), I receive a MAC address, and then if there's something connected on the other end I receive also an IP address (192.168.1.1 in my case, configured in static in NetworkManager). On the other end there are various instruments that wait for the DHCP server running on that PC to give them an IP.

The problem is that the DHCP server refuses to start if the subnet is not found, so it cannot be launched before the connection is up. How can I do systemctl restart isc-dhcp-server.service after I receive the IP 192.168.1.1 from NetworkManager ?

I thought of using a udev rule with ATTR{address}=="f0:1f:af:3d:6c:e7" RUN+="systemctl restart isc-dhcp-server.service" but it runs before the IP is assigned. Is there a udev option I can use or do I have to use another method via systemd or NetworkManager or other ?

I have a machine running Ubuntu Server 18.04. The network is configured using Netplan, so I have this config in /etc/netplan/01-netcfg.yaml:

network:
  version: 2
  renderer: networkd
  ethernets:
    enp1s0f0:
      optional: false
      addresses:
        - 10.0.0.1/24    
  wifis:
    wlp2s0:
      optional: true
      dhcp4: yes
      access-points:
        [...]

enp1s0f0 is connected to a device that may or may not be on (at boot or any other time). I want to run a DHCP server on this interface.

The trouble is, when I boot there's a delay of a few minutes and I see this message:

A start job is running for Wait for Network to be Configured

Eventually it times out, the boot continues, but enp1s0f0 is never configured or brought up. ip link show enp1s0f0 gives:

2: enp1s0f0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc mq state DOWN mode DEFAULT group default qlen 1000
    link/ether 10:dd:b1:ef:65:21 brd ff:ff:ff:ff:ff:ff

I have no idea what the significance of NO-CARRIER is, but in case it's relevant, here's the output of sudo lspci -v:

01:00.0 Ethernet controller: Broadcom Limited NetXtreme BCM57766 Gigabit Ethernet PCIe (rev 01)
    Subsystem: Broadcom Limited NetXtreme BCM57766 Gigabit Ethernet PCIe
    Flags: bus master, fast devsel, latency 0, IRQ 16
    Memory at a0400000 (64-bit, prefetchable) [size=64K]
    Memory at a0410000 (64-bit, prefetchable) [size=64K]
    Capabilities: [48] Power Management version 3
    Capabilities: [50] Vital Product Data
    Capabilities: [58] MSI: Enable- Count=1/8 Maskable- 64bit+
    Capabilities: [a0] MSI-X: Enable+ Count=6 Masked-
    Capabilities: [ac] Express Endpoint, MSI 00
    Capabilities: [100] Advanced Error Reporting
    Capabilities: [13c] Device Serial Number 00-00-10-dd-b1-ef-65-21
    Capabilities: [150] Power Budgeting <?>
    Capabilities: [160] Virtual Channel
    Capabilities: [1b0] Latency Tolerance Reporting
    Kernel driver in use: tg3
    Kernel modules: tg3

Now if I turn the attached device on, sure enough enp1s0f0 comes up:

2: enp1s0f0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP mode DEFAULT group default qlen 1000
    link/ether 10:dd:b1:ef:65:21 brd ff:ff:ff:ff:ff:ff

But it's of no use at this point — the DHCP server won't work, because it couldn't start with enp1s0f0 no up at boot time. I need enp1s0f0 up and configured during boot, which I thought was the whole point of a static IP configuration. Even stranger is that it always has an IPv6 address, even when it's down:

2: enp1s0f0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc mq state DOWN group default qlen 1000
    link/ether 10:dd:b1:ef:65:21 brd ff:ff:ff:ff:ff:ff
    inet6 fe80::12dd:b1ff:feef:6521/64 scope link 
       valid_lft forever preferred_lft forever

If I check Netplan's debug output, I see:

$ sudo netplan --debug apply
** (generate:1555): DEBUG: 20:39:27.253: Processing input file //etc/netplan/01-netcfg.yaml..
** (generate:1555): DEBUG: 20:39:27.254: starting new processing pass
** (generate:1555): DEBUG: 20:39:27.254: wlp2s0: adding wifi AP 'Jeff Winger's Wireless Hairbrush'
** (generate:1555): DEBUG: 20:39:27.254: wlp2s0: setting default backend to 1
** (generate:1555): DEBUG: 20:39:27.254: enp1s0f0: setting default backend to 1
** (generate:1555): DEBUG: 20:39:27.254: Generating output files..
** (generate:1555): DEBUG: 20:39:27.254: wlp2s0: Creating wpa_supplicant configuration file run/netplan/wpa-wlp2s0.conf
** (generate:1555): DEBUG: 20:39:27.254: Creating wpa_supplicant service enablement link /run/systemd/system/multi-user.target.wants/[email protected]
** (generate:1555): DEBUG: 20:39:27.254: NetworkManager: definition wlp2s0 is not for us (backend 1)
** (generate:1555): DEBUG: 20:39:27.254: NetworkManager: definition enp1s0f0 is not for us (backend 1)
DEBUG:netplan generated networkd configuration exists, restarting networkd
DEBUG:no netplan generated NM configuration exists
DEBUG:replug enp1s0f0: unbinding 0000:01:00.0 from /sys/bus/pci/drivers/tg3
DEBUG:replug enp1s0f0: rebinding 0000:01:00.0 to /sys/bus/pci/drivers/tg3
DEBUG:device wlp2s0 operstate is up, not replugging
DEBUG:netplan triggering .link rules for wlp2s0
DEBUG:device lo operstate is unknown, not replugging
DEBUG:netplan triggering .link rules for lo

My configuration for isc-dhcp-server is to have /etc/default/isc-dhcp-server contain:

INTERFACESv4="enp1s0f0"

...and /etc/dhcp/dhcpd.conf contain (amongst other things):

subnet 10.0.0.0 netmask 255.255.255.0 {
...
}

In theory, this should serve DHCP over enp1s0f0. However, since enp1s0f0 is never brought up, the DHCP server fails to start:

No subnet declaration for enp1s0f0 (no IPv4 addresses).
** Ignoring requests on enp1s0f0.  If this is not what
   you want, please write a subnet declaration
   in your dhcpd.conf file for the network segment
   to which interface enp1s0f0 is attached. **


Not configured to listen on any interfaces!

This wasn't an issue under ifupdown (I have no idea why enp1s0f0 doesn't just come up during boot, whether or not anything is at the other end of the cable; I thought that was the whole point of having a static IP). Is it possible to get it working in Netplan? Or is it possible to have the DHCP server start when enp1s0f0 is up?

Apparently the isc-dhcp-server is started too early in the boot sequence, it states that it has nothing to do. If I just log directly in as root and start it using the init.d-script, it starts normally.

My setup is basically an utterly standard router, with an eth0 on the inet side, and an eth1 on the lan side. However, I've defined a bridge instead of the eth1 for the lan-side. Thus, the lan-part of the network isn't up until the bridge is up.

I currently believe that the dhcp server is brought up before the bridge is brought up, probably because the bridge is brought up with the 'networking' task, while the eth's are taken up with the 'network-interface' tasks - which are run earlier. (also, the bridge takes a small age to get up compared to the eth's).

If I do take away the bridge config, instead using eth1 directly for the lan side, things work. (However, judging by syslog, things are still tight.)

Ideas of how the get DHCP to start later?

(The reason for the bridge, is to be able to use KVM with bridged networking..)

As I recall, there used to be this DHCP server called dhcpd3 However, under ubuntu, I am not entirely sure where to obtain or how to install it. The following command doesn't seem to locate the package.

apt-get install dhcpd3

Reading package lists... Done
Building dependency tree       
Reading state information... Done
E: Unable to locate package dhcpd3

Has dhcpd3 been deprecated and replaced by something else?

Thank you in advance!

I am running an Ubuntu 10.04 server installation and I recently had to switch it from DHCP to static ip. I edited /etc/network/interfaces file and switched

iface eth0 inet dhcp

to

iface eth0 inet static  
address 192.168.1.167  
netmask 255.255.255.240  
network 192.168.1.160  
broadcast 192.168.1.175  
gateway 192.168.1.161

You'll notice the IPs are a little strange. This is because the sever is now on a special subnet dedicated to isolating specific servers. I also edited the resolv.conf file to include the proper DNS servers (including one of Google's just in case all hell broke lose).

The problem is that, seemingly randomly, the machine will lose the ability to talk to the outside world. I know the machine is still up, but it acts like it has no networking at all. I think part of the issue is that there is no DHCP running to this subnet (nor will there be) and the dhclient seems to still be running on occasion which causes some sort of conflict (no idea what) which causes networking to die. I cannot, however, remove the dhcp3-client package as it also causes the ubuntu-minimal package to be removed and that would be bad.

So, any ideas? What might be calling the dhclient and what can I do to stop it from running?