Bug 1448987

Description of problem:

As per: https://bugzilla.redhat.com/show_bug.cgi?id=983325

NetworkManager will add a host route for the DHCP server. This is usually not a problem provided the customer has only one router per subnet, the default router. But if there are 2 routers on the same subnet and a new route has been defined for the subnet that the DHCP server is on, then this could present a problem depending on the customers external network configuration.

Take my LAB system, here we have where 10.7.1.66 is the dhcp server:

[root@unused ~]# ip addr

2: eno16780032: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP qlen 1000
    link/ether 00:50:56:a5:70:8a brd ff:ff:ff:ff:ff:ff
    inet 10.7.1.233/24 brd 10.7.1.255 scope global dynamic eno16780032
       valid_lft 259138sec preferred_lft 259138sec
    inet6 fe80::250:56ff:fea5:708a/64 scope link 
       valid_lft forever preferred_lft forever

[root@unused ~]# ip route 
default via 10.7.1.254 dev eno16780032  proto static  metric 100 
10.7.1.66 via 10.7.1.254 dev eno16780032  proto dhcp  metric 100 << added by NM
10.7.1.0/24 dev eno16780032  proto kernel  scope link  src 10.7.1.233 
[root@unused ~]# 

Now if we add a new route for the 10.0.0.0/8 subnet:

# ip route add 10.0.0.0/8 via 10.7.1.2 dev eno16780032

Now see how IP addresses for 10.7.1.x e.g 10.7.1.1 resolves. DHCP server 10.7.1.66 would also resolve the same, if the host route was not there:

# ip route get 10.7.1.1
10.7.1.1 via 10.7.1.2 src 10.7.1.233

But if we restart NM then it still adds a route for 10.7.1.66 via 10.7.1.254 instead of the new router 10.7.1.2. This can be a problem for customers that expect the traffic to go trough the new route.

Version-Release number of selected component (if applicable):

RHEL7

How reproducible:

Always see above.

Actual results:

When the routing table looks like:

# ip route 
default via 10.7.1.254 dev eno16780032  proto static  metric 100 
10.0.0.0/8 via 10.7.1.2 dev eno16780032
10.7.1.66 via 10.7.1.254 dev eno16780032  proto dhcp  metric 100 
10.7.1.0/24 dev eno16780032  proto kernel  scope link  src 10.7.1.233 

Then restarting NM still shows that the DCHP server host route is still via 10.7.1.254 instead of 10.7.1.2.

# ip route 
default via 10.7.1.254 dev eno16780032  proto static  metric 100 
10.0.0.0/8 via 10.7.1.2 dev eno16780032
10.7.1.66 via 10.7.1.254 dev eno16780032  proto dhcp  metric 100 
10.7.1.0/24 dev eno16780032  proto kernel  scope link  src 10.7.1.233 

Expected results:

After restarting, expect NM to find the new route for 10.7.1.66 pointing to gw 10.7.1.2. Just like "ip route get" e.g:

# ip route get 10.7.1.1
10.7.1.1 via 10.7.1.2 src 10.7.1.233

default via 10.7.1.254 dev eno16780032  proto static  metric 100 
10.0.0.0/8 via 10.7.1.2 dev eno16780032
10.7.1.66 via 10.7.1.2 dev eno16780032  proto dhcp  metric 100 
10.7.1.0/24 dev eno16780032  proto kernel  scope link  src 10.7.1.233 

Additional info:

We have a customer that reported this after trying to kickstart RHEL7 through Anaconda and the route added by NM is breaking communications because the new route they defined for the DHCP server network is not being used.