I'm begging for help here. Been spending hours researching how to solve what seemed like a simple problem:
On a CentOS 7.6 host with two network interfaces on two different networks, how to have two default gateways with a set metric to favour one of these interfaces. Can't do it. Would anybody please tell me what I'm missing before I have no hair left?
First, I've tried using the
METRIC=xxxsetting in/etc/sysconfig/network-scripts-/ifcfg-<interface>files based on some advice found on the web. Obviously if that ever was supported, it's no longer. Next.Then I've tried using policy-based routing following the tons of documentation that can be found online. Unfortunately very few mention adding metric values.
So, the full details (sorry it's long but I don't want to skip anything):
This machine has two active interfaces
enp10s4f0(IP10.149.247.23, prefix/24) andenp2s0f0(IP10.149.160.21, prefix/24).It has two gateways:
10.149.247.254and10.149.160.254. I want10.149.160.254to be the "best" gateway, therefore with the lower metric. I also want to avoid asymetric routing.I can reach my goal of having different metrics on gateways by means of entering routes with
ip route add default ... dev ... metricbut I want it to be persistent.
So I've created two routing tables in
/etc/iproute2/rt_tables:247 enp10s4f0table 160 enp2s0f0tableAnd I've made the following rule and route files in
/etc/sysconfig/network-scripts:route-enp10s4f0: 10.149.247.0/24 dev enp10s4f0 src 10.149.247.23 table enp10s4f0table default via 10.149.247.254 dev enp10s4f0 metric 110 table enp10s4f0table rule-enp10s4f0: from 10.149.247.23/32 table enp10s4f0table to 10.149.247.23 table enp10s4f0table route-enp2s0f0: 10.149.160.0/24 dev enp2s0f0 src 10.149.160.21 table enp2s0f0table default via 10.149.160.254 dev enp2s0f0 table enp2s0f0table rule-enp2s0f0: from 10.149.160.21/32 table enp2s0f0table to 10.149.160.21 table enp2s0f0table- Then I've used the proper incantations:
... and reboot.yum install NetworkManager-config-routing-rules systemctl enable NetworkManager-dispatcher.service systemctl start NetworkManager-dispatcher.service
Obviously the configuration is read and processed properly but the metric is not applied to the 10.149.247.254 gateway:
# ip route show table enp10s4f0table
default via 10.149.247.254 dev enp10s4f0 metric 110
10.149.247.0/24 dev enp10s4f0 scope link src 10.149.247.23
# ip route show table enp2s0f0table
default via 10.149.160.254 dev enp2s0f0
# ip rule show
0: from all lookup local
32762: from all to 10.149.160.21 lookup enp2s0f0table
32763: from 10.149.160.21 lookup enp2s0f0table
32764: from all to 10.149.247.23 lookup enp10s4f0table
32765: from 10.149.247.23 lookup enp10s4f0table
32766: from all lookup main
32767: from all lookup default
But:
# ip route show
default via 10.149.247.254 dev enp10s4f0 proto static metric 100
default via 10.149.160.254 dev enp2s0f0 proto static metric 102
10.149.160.0/24 dev enp2s0f0 proto kernel scope link src
10.149.160.21 metric 102
10.149.247.0/24 dev enp10s4f0 proto kernel scope link src
10.149.247.23 metric 100
192.168.2.0/24 dev enp10s4f1 proto kernel scope link src
192.168.2.14 metric 101
[OK, I do have a third interface enp10s4f1 but this one has DEFROUTE=no and no GATEWAY= in its ifcfg file so I haven't mentioned it so far]
See?
- No metric 110 on the
default via 10.149.247.254 dev enp10s4f0...line. - And the result is the exact opposite to what I'm trying to achieve:
enp10s4f0's default gateway has a lower metric thanenp2s0f0's
I can confirm this by tracerouting to a host outside of these two networks, packets do get out through 10.149.247.254
I'm stuck at this point. Can't figure it out. Please kindly help if you can.
