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IDProjectCategoryView StatusLast Update
0017413CentOS-8NetworkManagerpublic2020-05-28 20:34
Reporterdlimadaum 
PriorityhighSeverityblockReproducibilityalways
Status newResolutionopen 
Product Version8.1.1911 
Target VersionFixed in Version 
Summary0017413: Impossibile to use /31 address
DescriptionMigrating some servers from 7 to 8 I discovered a problem using /31 address on network interface.
Same configuration of the interface but it not start up, and logging in via console and trying to star the interface via ifup it stuck for a while and then exit with error.
"Connection activation failed: IP configuration could not be reserved (no available address, timeout, etc).
Tried also with the network-script and disabling the management of NetworkManager result in an error "Error adding default gateway <ip-of-the-gateway> for <interface-name>
It seems that the script set the broadcast address but in a /31 configuration no broadcast and no network address exist...so when it try to add the default route the gateway is the broadcast address...

If I configure the interface via ip command, it work fine without errors, because it not specify a broadcast address in the interface so the ip route add work without issue:

Interface configured with ifup:
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 7a:f1:2e:3c:d0:da brd ff:ff:ff:ff:ff:ff
    inet 46.20.84.242/31 brd 46.20.84.243 scope global eth0
       valid_lft forever preferred_lft forever
    inet6 fe80::78f1:2eff:fe3c:d0da/64 scope link
       valid_lft forever preferred_lft forever

Inteface configured with ip command:
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 7a:f1:2e:3c:d0:da brd ff:ff:ff:ff:ff:ff
    inet 46.20.84.242/31 scope global eth0
       valid_lft forever preferred_lft forever
    inet6 fe80::78f1:2eff:fe3c:d0da/64 scope link
       valid_lft forever preferred_lft forever

I think that also NetworkManager make the same mistake. The strange thing is that this configuration is working fine on a Centos7...
The only way to put a patch is to configure the interface with an external script at boot and disable completely NetworkManager and network-script.

Steps To ReproduceConfigure a /31 address on the interface.
Ifup interface-name

Additional InformationTo try with the ip command:
ip link set <interface-name> up
ip add add <ip-address>/31 dev eth0
ip route add default via <gateway> dev eth0
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Issue History

Date Modified Username Field Change
2020-05-28 20:34 dlimadaum New Issue