This is a typical interface configuration file in CentOS 7 which shows the following:
1- Which directives have to be commented out (if they exist)
2- The value of important parameters is highlighted ( BOOTPROTO, IPV6INIT, ONBOOT)
3- How multiple IPv4 can be added to the interface ( IPADDR0, PREFIX0, IPADDR1, PREFIX1, etc.)
4- How multiple IPv6 can be added to the interface ( IPV6ADDR_SECONDARIES )
[root@Node227 network-scripts]# cd /etc/sysconfig/network-scripts/
[root@Node227 network-scripts]# vi ifcfg-eno1
TYPE=Ethernet
BOOTPROTO=static
# DEFROUTE=yes
# IPV4_FAILURE_FATAL=no
IPV6INIT=yes
# IPV6_AUTOCONF=yes
# IPV6_DEFROUTE=yes
# IPV6_FAILURE_FATAL=no
NAME=eno1
UUID=e274defc-5b1e-4ce1-b171-24e84131b002
ONBOOT=yes
HWADDR=00:1E:C9:BA:AC:23
IPADDR0=199.x.x.x
PREFIX0=23
IPADDR1=199.x.x.x
PREFIX1=23
IPADDR2=199.x.x.x
PREFIX2=23
IPV6ADDR=26xx:xxxx:0:2::227/64
IPV6ADDR_SECONDARIES=”26xx:xxxx:0:2::2227/64 26xx:xxxx:0:2::4227/64″
# GATEWAY0=199.x.x.x
# DNS1=208.x.x.x
# DNS2=208.x.x.x
# IPV6_PEERDNS=yes
# IPV6_PEERROUTES=yes
In order for the changes to take effect we have to restart the network service.
# service network restart
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With the above configuration we verify both IPv4 and IPv6 on interface eno1
[root@Node227 network-scripts]# ip -4 addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN
inet 127.0.0.1/8 scope host lo
valid_lft forever preferred_lft forever
2: eno1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP qlen 1000
inet 199.x.x.x/23 brd 199.x.x.255 scope global eno1
valid_lft forever preferred_lft forever
inet 199.x.x.x/23 brd 199.x.x.255 scope global secondary eno1
valid_lft forever preferred_lft forever
inet 199.x.x.x/23 brd 199.x.x.255 scope global secondary eno1
valid_lft forever preferred_lft forever
[root@Node227 network-scripts]# ip -6 addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: eno1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qlen 1000
inet6 26xx:xxxx:0:2::4227/64 scope global
valid_lft forever preferred_lft forever
inet6 26xx:xxxx:0:2::2227/64 scope global
valid_lft forever preferred_lft forever
inet6 26xx:xxxx:0:2::227/64 scope global
valid_lft forever preferred_lft forever
inet6 fe80::21e:c9ff:feba:ac23/64 scope link
valid_lft forever preferred_lft forever
If multiple IPv4 are added to interface script they don’t show up in ifconfig but they are shown by ip addr show.
The other alternative is to create alias interfaces.
# cp ifcfg-eno1 ifcfg-eno1:1
# vi ifcfg-eno1:1
TYPE=Ethernet
BOOTPROTO=static
IPV6INIT=yes
NAME=eno1:1
# UUID=e274defc-5b1e-4ce1-b171-24e84131b002
ONBOOT=yes
HWADDR=00:1E:C9:BA:AC:23
IPADDR=199.x.x.x
PREFIX=23
[broadcast=199.x.x.255]
And if we want to do it from command line:
# ip addr add 199.x.x.x/23 [broadcast 199.x.x.255] dev eno1 label eno1:1
adding the broadcast address for alias interface is optional.
# ip -4 addr sh dev eno1
2: eno1: <BROADCAST,MULTICAST,PROMISC,UP,LOWER_UP> mtu 1500 qdisc mq state UP qlen 1000
inet 199.x.x.x/23 brd 199.x.x.255 scope global eno1
valid_lft forever preferred_lft forever
inet 199.x.x.x/23 brd 199.x.x.255 scope global secondary eno1
valid_lft forever preferred_lft forever
inet 199.x.x.149/23 scope global secondary eno1:1
valid_lft forever preferred_lft forever
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Configuring Gateway and DNS
In order to configure Gateway and DNS resolver we edit the file /etc/sysconfig/network
[root@Node227 network-scripts]# vi /etc/sysconfig/network
# Created by anaconda
GATEWAY=199.x.x.x
DNS1=208.x.x.x
DNS2=208.x.x.x
NETWORKING_IPV6=yes
IPV6_DEFAULTGW=26xx:x.x.x.x:0:2::1
IPV6_AUTOCONF=no
In order for the changes to take effect we have to restart the network service.
# service network restart
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Setting Hostname
In order to set the hostname we edit the file /etc/hostname
[root@Node227 network-scripts]# vi /etc/hostname
Node227
In order for this change to take effect the server has to be rebooted.
[root@Node227 network-scripts]# hostnamectl status
Static hostname: Node227 Icon name: computer-server Chassis: server Machine ID: f2c53cccb43c46cd9929dd58a0166023 Boot ID: 6d022c29c773440ea18c24659fea08d5 Operating System: CentOS Linux 7 (Core) CPE OS Name: cpe:/o:centos:centos:7 Kernel: Linux 3.10.0-229.11.1.el7.x86_64 Architecture: x86_64
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Disabling IPv6
If we want to disable IPv6 we remove all IPv6 configuration and change the following parameters
1- Set the value of parameter IPV6INIT in interface configuration file to “No”
2- set the value of the parameter NETWORKING_IPV6 in /etc/sysconfig/network to “No”
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In order for the changes in interface configuration file and /etc/sysconfig/network to take effect the network service has to be restarted:
[root@Node227 network-scripts]# service network restart
Restarting network (via systemctl): [ OK ]
or
[root@Node227 network-scripts]# systemctl restart network
[root@Node227 ~]# systemctl status network
network.service – LSB: Bring up/down networking
Loaded: loaded (/etc/rc.d/init.d/network)
Active: active (exited) since Fri 2015-08-07 12:40:54 EDT; 2s ago
Process: 2458 ExecStart=/etc/rc.d/init.d/network start (code=exited, status=0/SUCCESS)
Aug 07 12:40:54 Node227 network[2458]: RTNETLINK answers: File exists
Aug 07 12:40:54 Node227 network[2458]: RTNETLINK answers: File exists
Aug 07 12:40:54 Node227 network[2458]: RTNETLINK answers: File exists
Aug 07 12:40:54 Node227 network[2458]: RTNETLINK answers: File exists
Aug 07 12:40:54 Node227 network[2458]: RTNETLINK answers: File exists
Aug 07 12:40:54 Node227 network[2458]: RTNETLINK answers: File exists
Aug 07 12:40:54 Node227 network[2458]: RTNETLINK answers: File exists
Aug 07 12:40:54 Node227 network[2458]: RTNETLINK answers: File exists
Aug 07 12:40:54 Node227 network[2458]: RTNETLINK answers: File exists
Aug 07 12:40:54 Node227 systemd[1]: Started LSB: Bring up/down networking.
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Some advanced remarks that re not needed in a normal IP configuration but might be useful in some situations:
IPv4 range
In order to add an IPv4 range we can create the range interface.
However this seems to be buggy, it is not recommended.
[root@Node227 network-scripts]# cp ifcfg-eno1 ifcfg-eno1-range1
[root@Node227 network-scripts]# vi ifcfg-eno1-range1
TYPE=Ethernet
BOOTPROTO=static
NAME=eno1
UUID=e274defc-5b1e-4ce1-b171-24e84131b002
ONBOOT=yes
HWADDR=00:1E:C9:BA:AC:23
IPADDR_START=192.168.0.100
IPADDR_END=192.168.0.110
CLONENUM_START=1
PREFIX=24
In order for this to work we need to have IPV6ADDR_SECONDARIES defined in the main interface configuration in two lines as shown below:
IPV6ADDR_SECONDARIES=”26xx:xxxx:0:2::2227/64 26xx:xxxx:0:2::3227/64 \
26xx:xxxx:0:2::4227/64″
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Disabling NetworkManager
[root@Node227 ~]# service NetworkManager stop
Redirecting to /bin/systemctl stop NetworkManager.service
[root@Node227 ~]# chkconfig NetworkManager off
Note: Forwarding request to ‘systemctl disable NetworkManager.service’.
rm ‘/etc/systemd/system/multi-user.target.wants/NetworkManager.service’
rm ‘/etc/systemd/system/dbus-org.freedesktop.NetworkManager.service’
rm ‘/etc/systemd/system/dbus-org.freedesktop.nm-dispatcher.service’
[root@Node227 ~]# systemctl status NetworkManager
NetworkManager.service – Network Manager
Loaded: loaded (/usr/lib/systemd/system/NetworkManager.service; disabled)
Active: inactive (dead)
We also add the following directive to the interface configuration:
NM_CONTROLLED=no
By default the value of this parameter is “yes”
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Completely disabling IPv6
And there’s another problem…for some reason IPV6_AUTOCONF=no does not completely disable autoconf, it is still added to the interface when network is restarted (it is not added on the first interface activation). So I added some additional lines to my /sbin/ifup-pre-local:
if [ “$IPV6_AUTOCONF” = “no” ]; then
echo “0” > /proc/sys/net/ipv6/conf/default/autoconf
else
echo “1” > /proc/sys/net/ipv6/conf/default/autoconf
fi
net.ipv6.conf.default.autoconf in sysctl.conf
Disabling auto configuration; without setting the accept_ra, the system will autoconfigure using the Link local adress (fe80..)
sudo sysctl -w net.ipv6.conf.default.autoconf=0
sudo sysctl -w net.ipv6.conf.default.accept_ra=0
https://www.centos.org/forums/viewtopic.php?t=26754
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IPv4 and/or IPv6 forwarding
If forwarding is enabled, OS processes packets that their destination IP address doesn’t exist on the server and can pass a packet that has entered from one interface to another interface. This is vital for any kind of routing.
For IPv4:
# sysctl -w net.ipv4.ip_forward=1
or
# echo 1 > /proc/sys/net/ipv4/ip_forward
And in order to make it permanent we must add the following directive to /etc/sysctl.conf
net.ipv4.ip_forward = 1
# service network restart
For IPv6
We add the following directive to to/etc/sysconfig/network
IPv6FORWARDING=yes
# service network restart
This changes parameters such as net.ipv6.conf.all.forwarding and net.ipv6.conf.eth0.forwarding to 1. By default these parameters are zero and forwarding is disabled.
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