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This is not really a bug. Apparently, NetworkManager automatically calculates the broadcast address, which doesn't work with a /31. Are you sure you want to use a /31? Those are typically reserved for point-to-point links, used by routers. Using a /31, NetworkManager will assign the peer-end IP as the broadcast IP, and you wouldn't be able to communicate with the other side of the link. Since and 'Ethernet Network' is a broadcast network, and Ethernet Interface cannot be configured without a broadcast IP address. Here is an article that provide potential workarounds (https://1138blog.wordpress.com/2017/09/19/setting-up-31-interfaces-and-bgp-on-a-centos-machine/). RFC-3021 permits /31 for Point-to-point links! Conceptually, a 31-bit mask isn't valid on a broadcast network. |
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Yes, this is really a bug. Given the well-publicized shortage of routable IPv4 addresses, RFC3021 is one of many tools that network folk are using to try and eke as much useful life out of their respective IPv4 assignments as possible. Ethernet is not a broadcast network; it is a technology which supports broadcast - both directed and non-directed broadcast - sure, you lose the ability to run broadcast-dependent protocols across a /31 link but that is already warned about (and documented) in RFC3021. In a point-to-point Ethernet configuration, a packet sent by Host A will always be received by Host B and vice-versa. With regards to Ethernet not being configured without a broadcast IP address, yes, you are absolutely right but this particular issue was fixed in RHEL 6.3 by the upstream vendor as documented in https://bugzilla.redhat.com/show_bug.cgi?id=997271 The use of NM_CONTROLLED=no as suggested by your provided URL is indeed a valid workaround and one which does work; so, disabling NetworkManager across the board might be slightly overkill but as I believe that it is the upstream vendors' eventual intention to deprecate and discontinue support of network initscripts in favour of NetworkManager, it is better that there is as much compatibility between those two software components as possible in order to facilitate easier upgrades/migration in the future. I do realize that CentOS aims to be 'bug-for-bug' compatible with the upstream vendor's published binaries so I do not expect CentOS to make any changes to fix NetworkManager in response to this bug but if you do not wish to raise this as a bug in the upstream vendors' own Bugzilla instance, I am quite happy to do to that myself. |
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It's Bug In Centos 7 with kernel version [root@master-node ~]# uname -r 3.10.0-1062.12.1.el7.x86_64 assgin the IP address using nmcli and enable the ip followed the steps mention above fix the issue./ Now network manager is disable. all VM are working fine in network. |
- Anonymous
