Re: systemd-networkd bring interface up without link

[Andrei Borzenkov <arvidjaar@xxxxxxxxx>]

07.05.2019 4:22, Matt Zagrabelny пишет:
> Greetings,
> 
> I'm using Debian Buster with systemd 241-3.
> 
> I have a computer (server) that is running isc-dhcpd and I have a hardwired
> interface with static addressing on the computer:
> 
> $ cat /etc/systemd/network/eth-router.network
> [Match]
> MACAddress=00:01:c0:1e:25:dd
> 
> [Network]
> Address=172.20.20.1/24
> 
> $ ip a
> [...]
> 2: enp4s0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc mq state DOWN
> group default qlen 1000
>     link/ether 00:01:c0:1e:25:dd brd ff:ff:ff:ff:ff:ff
> [...]
> 
> When I connect another computer (laptop) to the server via an ethernet
> cable, the interface is brought up:
> 
> $ ip a
> [...]
> 2: enp4s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP
> group default qlen 1000
>     link/ether 00:01:c0:1e:25:dd brd ff:ff:ff:ff:ff:ff
>     inet 172.20.20.1/24 brd 172.20.20.255 scope global enp4s0
>        valid_lft forever preferred_lft forever
>     inet6 fe80::201:c0ff:fe1e:25dd/64 scope link
>        valid_lft forever preferred_lft forever
> 
> However isc-dhcpd is unhappy about trying to answer lease requests from an
> interface that doesn't have addressing - as isc-dhcpd has already started
> from boot and the interface is brought up when a client plugs into the
> ethernet cable:
> 
> Apr 25 18:14:48 zion dhcpd[651]: No subnet declaration for enp4s0 (no IPv4
> addresses).
> Apr 25 18:14:48 zion dhcpd[651]: ** Ignoring requests on enp4s0.  If this
> is not what
> Apr 25 18:14:48 zion dhcpd[651]:    you want, please write a subnet
> declaration
> Apr 25 18:14:48 zion dhcpd[651]:    in your dhcpd.conf file for the network
> segment
> Apr 25 18:14:48 zion dhcpd[651]:    to which interface enp4s0 is attached.
> **
> Apr 25 18:14:48 zion dhcpd[651]:
> 
> If I restart isc-dhcpd after the enp4s0 has an address, then my client
> computer (laptop) is able to request and get an address:
> 
> May 06 19:46:12 zion dhcpd[3654]: Server starting service.
> May 06 19:46:14 zion isc-dhcp-server[3641]: Starting ISC DHCPv4 server:
> dhcpd.
> May 06 19:46:14 zion systemd[1]: Started LSB: DHCP server.
> May 06 19:46:16 zion dhcpd[3654]: DHCPDISCOVER from c4:65:16:04:24:92 via
> enp4s0
> May 06 19:46:17 zion dhcpd[3654]: DHCPOFFER on 172.20.20.181 to
> c4:65:16:04:24:92 (tombstone) via enp4s0
> May 06 19:46:17 zion dhcpd[3654]: DHCPREQUEST for 172.20.20.181
> (172.20.20.1) from c4:65:16:04:24:92 (tombstone) via enp4s0
> May 06 19:46:17 zion dhcpd[3654]: DHCPACK on 172.20.20.181 to
> c4:65:16:04:24:92 (tombstone) via enp4s0
> 
> What is the proper way to handle this issue?
> 

I guess ISC DHCP support community would be better place to answer this.

> I also use the same isc-dhcpd to serve addresses out of a wifi interface,
> so I don't think I could have the service start up after a *.network file
> is activated - if that is the right terminology.
> 
> Is there a way to have systemd-network assign addressing to an interface
> without the link being up?
> 

man systemd.network

       ConfigureWithoutCarrier=
           A boolean. Allows networkd to configure a specific link even
if it has no
           carrier. Defaults to false.

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