How to manage DNS in NetworkManager via console (nmcli)

centos7nameservernetworkingnetworkmanager

I have CentOS 7.2 (guest in VirtualBox, vagrant box centos/7, no GUI).

I see there is a nameserver in file:

$ cat /etc/resolv.conf
# Generated by NetworkManager
nameserver 10.0.2.3

But how to add or replace with new one?

I have done this manually directly in the network:

$ vi /etc/sysconfig/network-scripts/ifcfg-eth0
PEERDS=no
DNS1=8.8.4.4
DNS2=8.8.8.8

And it works.

But is there any way to do this through nmcli?

P.S. No nmtui installed (in a selected system).

Best Answer

Here is the command to modify an existing connection.

nmcli con mod $connectionName ipv4.dns "8.8.8.8 8.8.4.4"

connectionName can be found by command: nmcli con. In the question case, it will be "System eth0"

If you want to ignore automatically configured nameservers and search domains, ie the settings passed from DHCP.

nmcli con mod $connectionName ipv4.ignore-auto-dns yes

Finally, to enable the changes, bring the connection down then up:

nmcli con down $connectionName
nmcli con up $connectionName

Verify with cat /etc/resolv.conf. You should not edit /etc/resolv.conf manually as it is generated by NetworkManager service, it is likely to get overridden at any given time.

Useful nmcli manual

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Linux – multicast routing – CentOS 5

I consider multicast routing kind of a black magic, but here are few shots ...

Check if igmpproxy creates the multicast route using ip mroute command.
If it does, your kernel is probably still filtering the input.
Most common cause is missing route to the source. Did you try disabling iptables? Or use TRACE target?
And if multicast route is not created I'd suggest using pimd (that's what I use for routing my IPTV multicasts).
And it seems you use altnet wrong. According to mrouted documentation, it means

Specifies an additional subnet (network) attached to the physical interface described in the phyint entry. mask_len is the length of the network mask.

Centos 6.2 Fresh ‘Basic Server’ install networking issues

Your routes and configuration look fine.

$: route -n
Destination // Gateway // Genmask // Flags // Metric // Ref // Use // Iface
66.*.*.0       0.0.0.0    255.255.255.248   U   1003      0   0     0  em2
0.0.0.0        66.*.*.1   0.0.0.0           UG     0      0   0     0  em2

The first route, 66.*.*.0/29 with gateway 0.0.0.0 tells your computer to use interface em2 and then make an arp request to find the hardware address of the host you're trying to reach. This is a "connected" route.

The second one is the default route, pointing at your default gateway through em2. If you need to send a packet in another network than 66.*.*.0/29, your computer will make an arp request to find 66.*.*.1 and then send the packets to it.

The only thing in your configuration that could be an issue is the NM_CONTROLLED=yes statement in /etc/sysconfig/network-scripts/ifcfg-em2. This tells the system that this interface is controlled by NetworkManager. This could interfere with your static configuration.

However, even without any default gateway you should be able to ping and ssh from the 66.*.*.0/29 subnet to your machine.

Check layer 1 first, and ensure that the cable is plugged on each side. Use leds on nic and switch, and check if the system sees it correctly:

# mii-tool
eth0: negotiated 1000baseT-FD flow-control, link ok

Then verify if any iptables are dropping the packets. Use iptables -L or iptables-save to check for any rules, and iptables -D <rule> to delete them. Pay attention to the default policy.

Also, on some systems, NetworkManager can configure ufw automatically, and I've had issues with static interface configuration that wasn't seen by NM and hence blocked by ufw.

Best Answer

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Linux – multicast routing – CentOS 5

Centos 6.2 Fresh ‘Basic Server’ install networking issues

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