Linux – Setting Metric on Default Route in RedHat

linuxlinux-networkingredhat

I have a Redhat server with 4 virtual networks.

The problem is when the server is setting up the networks, the IP routes gets the wrong metrics on the default routes.

I have tried creating a file called route-ens3 in /etc/sysconfig/network-scripts that looks like

192.168.3.1 dev ens3 metric 99

But that does not help 🙁

So how can I setup the metrics on the default ip route?
Do I have to change the name for the networks, so it comes in the order I want the metrics, as it looks like that is the way it is ordered at the moment?

Best Answer

What version of Red Hat are you using? If it's RHEL 7 or 8 you can use a simple NetworkManager command (or GUI) to set the route metric. Take a look at man nm-settings for the "route-metric" value.

You probably want to do something like this:

# nmcli connection modify "ens3" route-metric 99

https://people.freedesktop.org/~lkundrak/nm-docs/nm-settings.html

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Linux – backup static route on linux router

If you add 2 default routes with different metrics, this will switch the route only the case when main link is down and the other is up. The link is up (the interface status of the link) even if the router is not reachable. The link goes down only when the physical connection of the interface is down (e.g. no carrier detected, other out of band signaling).

What you really need is to detect when the remote router is down even if the link is up. This can be accomplished by using a dynamic routing protocol.

Another way would be to use a daemon or crontab script that will change the default route based on the reachability of the neighbor routers.

EDIT: The answer to your question is bellow. But this is not what you should configure to have redundancy.

ip route add default via R1 metric 100
ip route add default via R2 metric 200

If you need to make redundancy for the connection between R1 and R2 you should set LCAP as @growse wrote.

Linux – Advertise a Subnet Route with Radvd

I have found the problem.

Per default, the Linux kernel does only accept default routes via the router advertisement options in icmpv6.

To fix this, the correct kernel parameter must be set:

net.ipv6.conf.all.accept_ra_rt_info_max_plen = 128

From kernel docs:

accept_ra_rt_info_max_plen - INTEGER Maximum prefix length of Route Information in RA.

    Route Information w/ prefix larger than or equal to this
    variable shall be ignored.

    Functional default: 0 if accept_ra_rtr_pref is enabled.
                        -1 if accept_ra_rtr_pref is disabled.

Best Answer

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