A. 概要

IPv6を導入したくても導入できないネットワーク環境があります。このような環境でうっかりIPv6を有効にしてしまうと、yumアップデートがフリーズ等するなどの問題が発生します。本稿では、CentOS7.9、RHEL8.8、Ubuntu22環境での、IPv6無効化/再有効化の方法を解説します。

B. 解決したい課題

CentOS7.9、RHEL8.8、Ubuntu22環境で、IPv6無効化/再有効化したい。

C. 解決方法

CentOS7.9、RHEL8.8、Ubuntu22の順に、それぞれ、IPv6の、──①設定状態の確認、②無効化設定、③無効化後の確認、④再有効化設定、⑤再有効化後の確認──を解説します。

C.1 CentOS7.9で、IPv6を無効化/再有効化する

enp0s3がインターネットに抜けていけるインターフェースです。

現在のIPv6設定を確認します

# cat /etc/redhat-release
CentOS Linux release 7.9.2009 (Core)
# ifconfig enp0s3
enp0s3: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.1.43  netmask 255.255.255.0  broadcast 192.168.1.255
        inet6 240d:1a:b86:e800:443a:d3fa:1644:e55b  prefixlen 64  scopeid 0x0<global>
        inet6 fe80::777f:d335:e009:c9e0  prefixlen 64  scopeid 0x20<link>
        ether 08:00:27:aa:80:99  txqueuelen 1000  (Ethernet)
        RX packets 6425  bytes 8944887 (8.5 MiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 555  bytes 52301 (51.0 KiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         192.168.0.1     0.0.0.0         UG    100    0        0 enp0s3
192.168.1.0     0.0.0.0         255.255.255.0   U     100    0        0 enp0s3
（関係部分のみ抜粋）

inetにも、inet6にもアドレスが設定されています。

現在のIPv6設定の動作を確認します

# ping -c 3 -4 google.com
PING google.com (142.250.196.142) 56(84) bytes of data.
64 bytes from nrt12s36-in-f14.1e100.net (142.250.196.142): icmp_seq=1 ttl=116 time=5.16 ms
64 bytes from nrt12s36-in-f14.1e100.net (142.250.196.142): icmp_seq=2 ttl=116 time=4.38 ms
64 bytes from nrt12s36-in-f14.1e100.net (142.250.196.142): icmp_seq=3 ttl=116 time=4.04 ms

--- google.com ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2004ms
rtt min/avg/max/mdev = 4.044/4.528/5.162/0.474 ms
# ping -c 3 -6 google.com
PING google.com(nrt12s28-in-x0e.1e100.net (2404:6800:4004:810::200e)) 56 data bytes
64 bytes from nrt12s28-in-x0e.1e100.net (2404:6800:4004:810::200e): icmp_seq=1 ttl=116 time=5.35 ms
64 bytes from nrt12s28-in-x0e.1e100.net (2404:6800:4004:810::200e): icmp_seq=2 ttl=116 time=4.46 ms
64 bytes from nrt12s28-in-x0e.1e100.net (2404:6800:4004:810::200e): icmp_seq=3 ttl=116 time=4.39 ms

--- google.com ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2003ms
rtt min/avg/max/mdev = 4.396/4.737/5.352/0.439 ms

IPv4、IPv6ともにpingが届きます。

IPv6を無効化します

# nmcli c mod enp1s0f0 ipv6.method ignore
# systemctl restart NetworkManager

無効化後のIPv6設定を確認します

# ifconfig enp0s3
enp0s3: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.1.43  netmask 255.255.255.0  broadcast 192.168.1.255
        inet6 fe80::a00:27ff:feaa:8099  prefixlen 64  scopeid 0x20<link>
        ether 08:00:27:aa:80:99  txqueuelen 1000  (Ethernet)
        RX packets 6763  bytes 8973062 (8.5 MiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 741  bytes 74573 (72.8 KiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

inet6の設定は残っています（ちょっと紛らわしいです）

無効化後のIPv6動作を確認します

# ping -c 3 -4 google.com
PING google.com (142.250.196.110) 56(84) bytes of data.
64 bytes from nrt12s35-in-f14.1e100.net (142.250.196.110): icmp_seq=1 ttl=116 time=3.90 ms
64 bytes from nrt12s35-in-f14.1e100.net (142.250.196.110): icmp_seq=2 ttl=116 time=4.57 ms
64 bytes from nrt12s35-in-f14.1e100.net (142.250.196.110): icmp_seq=3 ttl=116 time=4.42 ms

--- google.com ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2005ms
rtt min/avg/max/mdev = 3.906/4.302/4.574/0.291 ms
# ping -c 3 -6 google.com
connect: ネットワークに届きません

IPv6のpingが疎通しなくなりました。

IPv6を再有効化します

# nmcli c mod enp1s0f0 ipv6.method auto
# systemctl restart NetworkManager

IPv6のアドレスの取得/設定方法を指定する必要があります。上例は「自動設定」です。

再有効化後のIPv6設定を確認します

# ifconfig enp0s3
enp0s3: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.1.43  netmask 255.255.255.0  broadcast 192.168.1.255
        inet6 240d:1a:b86:e800:443a:d3fa:1644:e55b  prefixlen 64  scopeid 0x0<global>
        inet6 fe80::a00:27ff:feaa:8099  prefixlen 64  scopeid 0x20<link>
        ether 08:00:27:aa:80:99  txqueuelen 1000  (Ethernet)
        RX packets 7212  bytes 9008616 (8.5 MiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 1023  bytes 103714 (101.2 KiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

inet6の変化がないので、ifconfigでは有効/無効が分かりません。

再有効化後のIPv6動作を確認します

# ping -c 3 -4 google.com
PING google.com (142.250.196.110) 56(84) bytes of data.
64 bytes from nrt12s35-in-f14.1e100.net (142.250.196.110): icmp_seq=1 ttl=116 time=3.92 ms
64 bytes from nrt12s35-in-f14.1e100.net (142.250.196.110): icmp_seq=2 ttl=116 time=4.23 ms
64 bytes from nrt12s35-in-f14.1e100.net (142.250.196.110): icmp_seq=3 ttl=116 time=4.16 ms

--- google.com ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2004ms
rtt min/avg/max/mdev = 3.920/4.104/4.234/0.153 ms
# ping -c 3 -6 google.com
PING google.com(nrt12s35-in-x0e.1e100.net (2404:6800:4004:821::200e)) 56 data bytes
64 bytes from nrt12s35-in-x0e.1e100.net (2404:6800:4004:821::200e): icmp_seq=1 ttl=58 time=5.82 ms
64 bytes from nrt12s35-in-x0e.1e100.net (2404:6800:4004:821::200e): icmp_seq=2 ttl=58 time=4.59 ms
64 bytes from nrt12s35-in-x0e.1e100.net (2404:6800:4004:821::200e): icmp_seq=3 ttl=58 time=4.44 ms

--- google.com ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2005ms
rtt min/avg/max/mdev = 4.443/4.951/5.822/0.623 ms

IPv4、IPv6ともにpingが届くようになりました。

C.2 RHEL8.8で、IPv6を無効化/再有効化する

enp1s0f0がインターネットに抜けていけるインターフェースです

現在のIPv6設定を確認します

# cat /etc/redhat-release
Red Hat Enterprise Linux release 8.8 (Ootpa)
# ifconfig enp1s0f0
enp1s0f0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.1.123  netmask 255.255.255.0  broadcast 192.168.1.255
        inet6 fe80::a236:9fff:fe8e:41b4  prefixlen 64  scopeid 0x20<link>
        inet6 240d:1a:b86:e800:a236:9fff:fe8e:41b4  prefixlen 64  scopeid 0x0<global>
        ether a0:36:9f:8e:41:b4  txqueuelen 1000  (Ethernet)
        RX packets 1488726  bytes 1568795131 (1.4 GiB)
        RX errors 0  dropped 20  overruns 0  frame 0
        TX packets 566324  bytes 191670708 (182.7 MiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
        device memory 0xdf100000-df1fffff
# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         192.168.1.1     0.0.0.0         UG    101    0        0 enp1s0f0
192.168.1.0     0.0.0.0         255.255.255.0   U     101    0        0 enp1s0f0
（関係部分のみ抜粋）

inetにも、inet6にもアドレスが設定されています。

現在のIPv6設定の動作を確認します

# ping -c 3 -4 google.com
PING google.com (142.250.196.142) 56(84) bytes of data.
64 bytes from nrt12s36-in-f14.1e100.net (142.250.196.142): icmp_seq=1 ttl=117 time=3.19 ms
64 bytes from nrt12s36-in-f14.1e100.net (142.250.196.142): icmp_seq=2 ttl=117 time=3.46 ms
64 bytes from nrt12s36-in-f14.1e100.net (142.250.196.142): icmp_seq=3 ttl=117 time=3.23 ms

--- google.com ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2002ms
rtt min/avg/max/mdev = 3.194/3.293/3.455/0.132 ms
# ping -c 3 -6 google.com
PING google.com(nrt12s36-in-x0e.1e100.net (2404:6800:4004:822::200e)) 56 data bytes
64 bytes from nrt12s36-in-x0e.1e100.net (2404:6800:4004:822::200e): icmp_seq=1 ttl=58 time=4.32 ms
64 bytes from nrt12s36-in-x0e.1e100.net (2404:6800:4004:822::200e): icmp_seq=2 ttl=58 time=3.58 ms
64 bytes from nrt12s36-in-x0e.1e100.net (2404:6800:4004:822::200e): icmp_seq=3 ttl=58 time=3.65 ms

--- google.com ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2004ms
rtt min/avg/max/mdev = 3.578/3.847/4.320/0.342 ms

IPv4、IPv6ともにpingが届きます。

IPv6を無効化します

# nmcli c mod enp1s0f0 ipv6.method disable
# systemctl restart NetworkManager

ipv6.method disableがサポートされてない古いRHEL8.Xバージョンでは、ipv6.method ignoreを指定します。

無効化後のIPv6設定を確認します

# ifconfig enp1s0f0
enp1s0f0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.1.123  netmask 255.255.255.0  broadcast 192.168.1.255
        ether a0:36:9f:8e:41:b4  txqueuelen 1000  (Ethernet)
        RX packets 1496291  bytes 1570491500 (1.4 GiB)
        RX errors 0  dropped 21  overruns 0  frame 0
        TX packets 572846  bytes 192855030 (183.9 MiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
        device memory 0xdf100000-df1fffff

inet6の設定が削除されました。

無効化後のIPv6動作を確認します

# ping -c 3 -4 google.com
PING google.com (142.250.196.110) 56(84) bytes of data.
64 bytes from nrt12s35-in-f14.1e100.net (142.250.196.110): icmp_seq=1 ttl=117 time=3.30 ms
64 bytes from nrt12s35-in-f14.1e100.net (142.250.196.110): icmp_seq=2 ttl=117 time=3.20 ms
64 bytes from nrt12s35-in-f14.1e100.net (142.250.196.110): icmp_seq=3 ttl=117 time=3.11 ms

--- google.com ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2003ms
rtt min/avg/max/mdev = 3.114/3.206/3.302/0.100 ms
# ping -c 3 -6 google.com
connect: Network is unreachable

IPv6のpingが疎通しなくなりました。

IPv6を再有効化します

# nmcli c mod enp1s0f0 ipv6.method auto
# systemctl restart NetworkManager

IPv6のアドレスの取得/設定方法を指定する必要があります。上例は「自動設定」です。

再有効化後のIPv6設定を確認します

# ifconfig enp1s0f0
enp1s0f0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.1.123  netmask 255.255.255.0  broadcast 192.168.1.255
        inet6 fe80::a236:9fff:fe8e:41b4  prefixlen 64  scopeid 0x20<link>
        inet6 240d:1a:b86:e800:a236:9fff:fe8e:41b4  prefixlen 64  scopeid 0x0<global>
        ether a0:36:9f:8e:41:b4  txqueuelen 1000  (Ethernet)
        RX packets 1499728  bytes 1571232879 (1.4 GiB)
        RX errors 0  dropped 21  overruns 0  frame 0
        TX packets 575824  bytes 193334401 (184.3 MiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
        device memory 0xdf100000-df1fffff

inet6のアドレス情報が再設定されました。

再有効化後のIPv6動作を確認します

# ping -c 3 -4 google.com
PING google.com (142.250.198.14) 56(84) bytes of data.
64 bytes from nrt12s58-in-f14.1e100.net (142.250.198.14): icmp_seq=1 ttl=117 time=3.15 ms
64 bytes from nrt12s58-in-f14.1e100.net (142.250.198.14): icmp_seq=2 ttl=117 time=3.26 ms
64 bytes from nrt12s58-in-f14.1e100.net (142.250.198.14): icmp_seq=3 ttl=117 time=3.11 ms

--- google.com ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2002ms
rtt min/avg/max/mdev = 3.106/3.170/3.256/0.078 ms
# ping -c 3 -6 google.com
PING google.com(nrt12s36-in-x0e.1e100.net (2404:6800:4004:822::200e)) 56 data bytes
64 bytes from nrt12s36-in-x0e.1e100.net (2404:6800:4004:822::200e): icmp_seq=1 ttl=58 time=4.50 ms
64 bytes from nrt12s36-in-x0e.1e100.net (2404:6800:4004:822::200e): icmp_seq=2 ttl=58 time=3.70 ms
64 bytes from nrt12s36-in-x0e.1e100.net (2404:6800:4004:822::200e): icmp_seq=3 ttl=58 time=3.59 ms

--- google.com ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2003ms
rtt min/avg/max/mdev = 3.589/3.929/4.500/0.406 ms

IPv4、IPv6ともにpingが届くようになりました。

C.3 Ubuntu22で、IPv6を無効化/再有効化する

enps03がインターネットに抜けていけるインターフェースです

NetworkManager環境を構築します

UbuntuはデフォルトではNetworkManager環境が設定されてないので、設定します。

# apt install network-manager
# systemctl status NetworkManager
● NetworkManager.service - Network Manager
     Loaded: loaded (/lib/systemd/system/NetworkManager.service; enabled; vendor preset: enabled)
     Active: active (running) since Fri 2023-09-08 06:07:06 UTC; 19s ago
       Docs: man:NetworkManager(8)
   Main PID: 1780 (NetworkManager)
      Tasks: 3 (limit: 40062)
     Memory: 3.1M
        CPU: 44ms
     CGroup: /system.slice/NetworkManager.service
             └─1780 /usr/sbin/NetworkManager --no-daemon
（以下省略）

/etc/netplan/00-installer-config.yamlを編集します。
version: 2とrenderer: NetworkManagerの行を追加します。

# This is the network config written by 'subiquity'
network:
  version: 2
  renderer: NetworkManager

編集後リブートして、nmcliコマンドが正常動作することを確認します。

# nmcli c show
NAME            UUID                                  TYPE      DEVICE
netplan-enp0s3  1eef7e45-3b9d-3043-bee3-fc5925c90273  ethernet  enp0s3

現在のIPv6設定を確認します

# cat /etc/lsb-release
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=22.04
DISTRIB_CODENAME=jammy
DISTRIB_DESCRIPTION="Ubuntu 22.04.3 LTS"

# ifconfig enp0s3
enp0s3: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.1.42  netmask 255.255.255.0  broadcast 192.168.1.255
        inet6 fe80::a00:27ff:fe6d:1c43  prefixlen 64  scopeid 0x20<link>
        inet6 240d:1a:b86:e800:a00:27ff:fe6d:1c43  prefixlen 64  scopeid 0x0<global>
        ether 08:00:27:6d:1c:43  txqueuelen 1000  (Ethernet)
        RX packets 510  bytes 317588 (317.5 KB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 287  bytes 33136 (33.1 KB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         192.168.1.1     0.0.0.0         UG    0      0        0 enp0s3
192.168.1.0     0.0.0.0         255.255.255.0   U     0      0        0 enp0s3
（関係部分のみ抜粋）

inetにも、inet6にもアドレスが設定されています。

現在のIPv6設定の動作を確認します

# apt-get install iputils-ping net-tools
# ping -c 3 -4 google.com
PING  (142.250.196.110) 56(84) bytes of data.
64 bytes from nrt12s35-in-f14.1e100.net (142.250.196.110): icmp_seq=1 ttl=117 time=4.69 ms
64 bytes from nrt12s35-in-f14.1e100.net (142.250.196.110): icmp_seq=2 ttl=117 time=4.22 ms
64 bytes from nrt12s35-in-f14.1e100.net (142.250.196.110): icmp_seq=3 ttl=117 time=4.10 ms

---  ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2002ms
rtt min/avg/max/mdev = 4.101/4.336/4.691/0.255 ms
# ping -c 3 -6 google.com
PING google.com(nrt12s35-in-x0e.1e100.net (2404:6800:4004:821::200e)) 56 data bytes
64 bytes from nrt12s35-in-x0e.1e100.net (2404:6800:4004:821::200e): icmp_seq=1 ttl=117 time=3.85 ms
64 bytes from nrt12s35-in-x0e.1e100.net (2404:6800:4004:821::200e): icmp_seq=2 ttl=117 time=4.26 ms
64 bytes from nrt12s35-in-x0e.1e100.net (2404:6800:4004:821::200e): icmp_seq=3 ttl=117 time=4.14 ms

--- google.com ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2004ms
rtt min/avg/max/mdev = 3.847/4.082/4.255/0.172 ms

pingがインストールされてない場合は、iputils-ping net-toolsをインストールしておきます。
IPv4、IPv6ともにpingが届きます。

IPv6を無効化します

# nmcli c mod netplan-enp0s3 ipv6.method disable
# systemctl restart NetworkManager

無効化後のIPv6設定を確認します

# ifconfig enp0s3
enp0s3: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.1.42  netmask 255.255.255.0  broadcast 192.168.1.255
        ether 08:00:27:6d:1c:43  txqueuelen 1000  (Ethernet)
        RX packets 308  bytes 29193 (29.1 KB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 168  bytes 20875 (20.8 KB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

inet6の設定が削除されました。

無効化後のIPv6動作を確認します

# ping -c 3 -4 google.com
PING google.com (142.250.198.14) 56(84) bytes of data.
64 bytes from nrt12s58-in-f14.1e100.net (142.250.198.14): icmp_seq=1 ttl=117 time=3.85 ms
64 bytes from nrt12s58-in-f14.1e100.net (142.250.198.14): icmp_seq=2 ttl=117 time=4.13 ms
64 bytes from nrt12s58-in-f14.1e100.net (142.250.198.14): icmp_seq=3 ttl=117 time=3.98 ms

--- google.com ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2004ms
rtt min/avg/max/mdev = 3.854/3.988/4.132/0.113 ms
# ping -c 3 -6 google.com
ping: connect: Network is unreachable

IPv6のpingが疎通しなくなりました。

IPv6を再有効化します

# nmcli c mod netplan-enp0s3 ipv6.method auto
# systemctl restart NetworkManager

IPv6のアドレスの取得/設定方法を指定する必要があります。上例は「自動設定」です。

再有効化後のIPv6設定を確認します

# ifconfig enp0s3
enp0s3: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.1.42  netmask 255.255.255.0  broadcast 192.168.1.255
        inet6 fe80::a00:27ff:fe6d:1c43  prefixlen 64  scopeid 0x20<link>
        inet6 240d:1a:b86:e800:9e67:bc57:fffe:ccc3  prefixlen 64  scopeid 0x0<global>
        inet6 240d:1a:b86:e800:a00:27ff:fe6d:1c43  prefixlen 64  scopeid 0x0<global>
        ether 08:00:27:6d:1c:43  txqueuelen 1000  (Ethernet)
        RX packets 458  bytes 41510 (41.5 KB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 263  bytes 32191 (32.1 KB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

inet6のアドレス情報が再設定されました。

再有効化後のIPv6動作を確認します

# ping -c 3 -4 google.com
PING  (142.250.196.142) 56(84) bytes of data.
64 bytes from nrt12s36-in-f14.1e100.net (142.250.196.142): icmp_seq=1 ttl=117 time=3.62 ms
64 bytes from nrt12s36-in-f14.1e100.net (142.250.196.142): icmp_seq=2 ttl=117 time=4.37 ms
64 bytes from nrt12s36-in-f14.1e100.net (142.250.196.142): icmp_seq=3 ttl=117 time=4.06 ms

---  ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2006ms
rtt min/avg/max/mdev = 3.624/4.015/4.366/0.304 ms
# ping -c 3 -6 google.com
PING google.com(nrt12s35-in-x0e.1e100.net (2404:6800:4004:821::200e)) 56 data bytes
64 bytes from nrt12s35-in-x0e.1e100.net (2404:6800:4004:821::200e): icmp_seq=1 ttl=117 time=5.23 ms
64 bytes from nrt12s35-in-x0e.1e100.net (2404:6800:4004:821::200e): icmp_seq=2 ttl=117 time=4.07 ms
64 bytes from nrt12s35-in-x0e.1e100.net (2404:6800:4004:821::200e): icmp_seq=3 ttl=117 time=4.35 ms

--- google.com ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2004ms
rtt min/avg/max/mdev = 4.074/4.551/5.225/0.490 ms

IPv4、IPv6ともにpingが届くようになりました。

以上