Generally, ifupdown is no longer recommended (or supported). It's recommended to move to netplan, or at least to directly configuring networkd or network-manager.
For your specific issue, it's been a while since I looked at ifupdown, but from an old bug comment: https://bugs.launchpad.net/ubuntu/+source/ifupdown/+bug/1628552/comments/9 I think ifupdown static configuration of dns does not work with systemd- resolved; you must have resolvconf installed for that to work (since resolvconf installs the ifupdown hook, while resolved ignores ifupdown completely). Maybe your system upgrade removed the resolvconf package? ** Changed in: systemd (Ubuntu) Status: New => Incomplete -- You received this bug notification because you are a member of Ubuntu Touch seeded packages, which is subscribed to systemd in Ubuntu. https://bugs.launchpad.net/bugs/1883412 Title: 20.04: DNS servers from /etc/network/interfaces not honored by systemd-resolve Status in systemd package in Ubuntu: Incomplete Bug description: I have a server that uses /etc/network/interfaces to configure static IP info, including DNS, via /etc/network/interfaces. This worked fine in 16.04 and 18.04. However, when I updated to 20.04 this no longer works; I have to run "systemd-resolve --set-dns=192.168.63.1 --interface=enp3s0" to fix it after every boot. My /etc/network/interfaces is: ==================== # Loopback auto lo iface lo inet loopback # enp3s0: LAN (Motherboard) auto enp3s0 iface enp3s0 inet static address 192.168.63.2 netmask 255.255.255.0 network 192.168.63.0 broadcast 192.168.63.255 gateway 192.168.63.1 dns-nameservers 192.168.63.1 iface enp3s0 inet6 static address 2001:470:bb52:63::2/64 netmask 64 # WiFi USB # FIXME: Probably will get renamed on boot #allow-hotplug ethFlashAirWifi #iface ethFlashAirWifi inet manual ==================== "systemd-resolve --status" outputs the following beforr I run the WAR command given above: ==================== Global LLMNR setting: no MulticastDNS setting: no DNSOverTLS setting: no DNSSEC setting: no DNSSEC supported: no DNSSEC NTA: 10.in-addr.arpa 16.172.in-addr.arpa 168.192.in-addr.arpa 17.172.in-addr.arpa 18.172.in-addr.arpa 19.172.in-addr.arpa 20.172.in-addr.arpa 21.172.in-addr.arpa 22.172.in-addr.arpa 23.172.in-addr.arpa 24.172.in-addr.arpa 25.172.in-addr.arpa 26.172.in-addr.arpa 27.172.in-addr.arpa 28.172.in-addr.arpa 29.172.in-addr.arpa 30.172.in-addr.arpa 31.172.in-addr.arpa corp d.f.ip6.arpa home internal intranet lan local private test Link 4 (tun0) Current Scopes: none DefaultRoute setting: no LLMNR setting: yes MulticastDNS setting: no DNSOverTLS setting: no DNSSEC setting: no DNSSEC supported: no Link 3 (lxcbr0) Current Scopes: none DefaultRoute setting: no LLMNR setting: yes MulticastDNS setting: no DNSOverTLS setting: no DNSSEC setting: no DNSSEC supported: no Link 2 (enp3s0) Current Scopes: none DefaultRoute setting: no LLMNR setting: yes MulticastDNS setting: no DNSOverTLS setting: no DNSSEC setting: no DNSSEC supported: no ==================== ProblemType: Bug DistroRelease: Ubuntu 20.04 Package: systemd 245.4-4ubuntu3.1 ProcVersionSignature: Ubuntu 5.4.0-37.41-generic 5.4.41 Uname: Linux 5.4.0-37-generic x86_64 ApportVersion: 2.20.11-0ubuntu27.2 Architecture: amd64 CasperMD5CheckResult: skip Date: Sun Jun 14 01:58:10 2020 InstallationDate: Installed on 2016-04-12 (1524 days ago) InstallationMedia: Ubuntu-Server 16.04 LTS "Xenial Xerus" - Beta amd64 (20160408) MachineType: To Be Filled By O.E.M. To Be Filled By O.E.M. ProcEnviron: TERM=xterm-256color PATH=(custom, no user) XDG_RUNTIME_DIR=<set> LANG=en_US.UTF-8 SHELL=/bin/bash ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-5.4.0-37-generic root=/dev/mapper/severn_vg2016-lv_root ro SourcePackage: systemd UpgradeStatus: Upgraded to focal on 2020-06-14 (0 days ago) dmi.bios.date: 06/18/2010 dmi.bios.vendor: American Megatrends Inc. dmi.bios.version: P2.40 dmi.board.name: 890GX Extreme3 dmi.board.vendor: ASRock dmi.chassis.asset.tag: To Be Filled By O.E.M. dmi.chassis.type: 3 dmi.chassis.vendor: To Be Filled By O.E.M. dmi.chassis.version: To Be Filled By O.E.M. dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvrP2.40:bd06/18/2010:svnToBeFilledByO.E.M.:pnToBeFilledByO.E.M.:pvrToBeFilledByO.E.M.:rvnASRock:rn890GXExtreme3:rvr:cvnToBeFilledByO.E.M.:ct3:cvrToBeFilledByO.E.M.: dmi.product.family: To Be Filled By O.E.M. dmi.product.name: To Be Filled By O.E.M. dmi.product.sku: To Be Filled By O.E.M. dmi.product.version: To Be Filled By O.E.M. dmi.sys.vendor: To Be Filled By O.E.M. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1883412/+subscriptions -- Mailing list: https://launchpad.net/~touch-packages Post to : touch-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~touch-packages More help : https://help.launchpad.net/ListHelp
