[Bug 1959445] [NEW] DHCPD gets confused about what IPs should be handed out on what interfaces

[Daniel C]

Public bug reported:

I had a device request an IP on one VLAN (one interface associated with
the server -- ens256), and then I moved the device to a different VLAN
(interface ens192 on the server), and was surprised when the DHCPD
process continued to hand out the same IP on the new VLAN.

Here are the associated syslog entries, and the IP interface settings:

Jan 28 12:06:35 backup dhcpd[1020678]: DHCPREQUEST for 10.2.195.100 from ec:02:73:b8:4d:01 via ens256
Jan 28 12:06:35 backup dhcpd[1020678]: DHCPACK on 10.2.195.100 to ec:02:73:b8:4d:01 via ens256
Jan 28 12:08:43 backup dhcpd[1020678]: DHCPREQUEST for 10.2.195.100 from ec:02:73:b8:4d:01 via ens256
Jan 28 12:08:43 backup dhcpd[1020678]: DHCPACK on 10.2.195.100 to ec:02:73:b8:4d:01 via ens256
Jan 28 12:11:08 backup dhcpd[1024746]: DHCPREQUEST for 10.2.195.100 from ec:02:73:b8:4d:01 via ens192
Jan 28 12:11:08 backup dhcpd[1024746]: DHCPACK on 10.2.195.100 to ec:02:73:b8:4d:01 via ens192
Jan 28 12:11:23 backup dhcpd[1024746]: DHCPREQUEST for 10.2.195.100 from ec:02:73:b8:4d:01 via ens192
Jan 28 12:11:23 backup dhcpd[1024746]: DHCPACK on 10.2.195.100 to ec:02:73:b8:4d:01 via ens192

(I've trimmed out the IPv6 information):
backup$ ip addr list
...
3: ens192: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
    link/ether 00:50:56:9e:8b:d8 brd ff:ff:ff:ff:ff:ff
    inet 10.7.32.2/21 brd 10.7.39.255 scope global ens192
       valid_lft forever preferred_lft forever
...
5: ens256: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
    link/ether 00:50:56:9e:f2:e6 brd ff:ff:ff:ff:ff:ff
    inet 10.2.195.2/24 brd 10.2.195.255 scope global ens256
       valid_lft forever preferred_lft forever
...

When I rebooted the client, it went back to DHCPDISCOVER mode and then
the DHCPD daemon correctly recognized that this client was on a new
interface/VLAN and handed it a valid IP address for that interface/VLAN.

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: isc-dhcp-server 4.4.1-2.1ubuntu5.20.04.2 [modified: usr/bin/omshell]
ProcVersionSignature: Ubuntu 5.4.0-94.106-generic 5.4.157
Uname: Linux 5.4.0-94-generic x86_64
ApportVersion: 2.20.11-0ubuntu27.21
Architecture: amd64
CasperMD5CheckResult: pass
Date: Fri Jan 28 12:24:05 2022
InstallationDate: Installed on 2021-06-29 (212 days ago)
InstallationMedia: Ubuntu-Server 20.04.1 LTS "Focal Fossa" - Release amd64 (20200731)
ProcEnviron:
 SHELL=/bin/bash
 TERM=xterm-color
 XDG_RUNTIME_DIR=<set>
 PATH=(custom, user)
SourcePackage: isc-dhcp
UpgradeStatus: No upgrade log present (probably fresh install)
modified.conffile..etc.dhcp.dhcpd6.conf: [modified]
mtime.conffile..etc.dhcp.dhcpd.conf: 2022-01-28T12:09:41.747865
mtime.conffile..etc.dhcp.dhcpd6.conf: 2019-01-03T15:05:49

** Affects: isc-dhcp (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: amd64 apport-bug focal uec-images

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https://bugs.launchpad.net/bugs/1959445

Title:
  DHCPD gets confused about what IPs should be handed out on what
  interfaces

Status in isc-dhcp package in Ubuntu:
  New

Bug description:
  I had a device request an IP on one VLAN (one interface associated
  with the server -- ens256), and then I moved the device to a different
  VLAN (interface ens192 on the server), and was surprised when the
  DHCPD process continued to hand out the same IP on the new VLAN.

  Here are the associated syslog entries, and the IP interface settings:

  Jan 28 12:06:35 backup dhcpd[1020678]: DHCPREQUEST for 10.2.195.100 from ec:02:73:b8:4d:01 via ens256
  Jan 28 12:06:35 backup dhcpd[1020678]: DHCPACK on 10.2.195.100 to ec:02:73:b8:4d:01 via ens256
  Jan 28 12:08:43 backup dhcpd[1020678]: DHCPREQUEST for 10.2.195.100 from ec:02:73:b8:4d:01 via ens256
  Jan 28 12:08:43 backup dhcpd[1020678]: DHCPACK on 10.2.195.100 to ec:02:73:b8:4d:01 via ens256
  Jan 28 12:11:08 backup dhcpd[1024746]: DHCPREQUEST for 10.2.195.100 from ec:02:73:b8:4d:01 via ens192
  Jan 28 12:11:08 backup dhcpd[1024746]: DHCPACK on 10.2.195.100 to ec:02:73:b8:4d:01 via ens192
  Jan 28 12:11:23 backup dhcpd[1024746]: DHCPREQUEST for 10.2.195.100 from ec:02:73:b8:4d:01 via ens192
  Jan 28 12:11:23 backup dhcpd[1024746]: DHCPACK on 10.2.195.100 to ec:02:73:b8:4d:01 via ens192

  (I've trimmed out the IPv6 information):
  backup$ ip addr list
  ...
  3: ens192: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
      link/ether 00:50:56:9e:8b:d8 brd ff:ff:ff:ff:ff:ff
      inet 10.7.32.2/21 brd 10.7.39.255 scope global ens192
         valid_lft forever preferred_lft forever
  ...
  5: ens256: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
      link/ether 00:50:56:9e:f2:e6 brd ff:ff:ff:ff:ff:ff
      inet 10.2.195.2/24 brd 10.2.195.255 scope global ens256
         valid_lft forever preferred_lft forever
  ...

  When I rebooted the client, it went back to DHCPDISCOVER mode and then
  the DHCPD daemon correctly recognized that this client was on a new
  interface/VLAN and handed it a valid IP address for that
  interface/VLAN.

  ProblemType: Bug
  DistroRelease: Ubuntu 20.04
  Package: isc-dhcp-server 4.4.1-2.1ubuntu5.20.04.2 [modified: usr/bin/omshell]
  ProcVersionSignature: Ubuntu 5.4.0-94.106-generic 5.4.157
  Uname: Linux 5.4.0-94-generic x86_64
  ApportVersion: 2.20.11-0ubuntu27.21
  Architecture: amd64
  CasperMD5CheckResult: pass
  Date: Fri Jan 28 12:24:05 2022
  InstallationDate: Installed on 2021-06-29 (212 days ago)
  InstallationMedia: Ubuntu-Server 20.04.1 LTS "Focal Fossa" - Release amd64 (20200731)
  ProcEnviron:
   SHELL=/bin/bash
   TERM=xterm-color
   XDG_RUNTIME_DIR=<set>
   PATH=(custom, user)
  SourcePackage: isc-dhcp
  UpgradeStatus: No upgrade log present (probably fresh install)
  modified.conffile..etc.dhcp.dhcpd6.conf: [modified]
  mtime.conffile..etc.dhcp.dhcpd.conf: 2022-01-28T12:09:41.747865
  mtime.conffile..etc.dhcp.dhcpd6.conf: 2019-01-03T15:05:49

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