Netmask On Aliases Overriden By Netmask On Interface
CentOS-6.10
We have a host with the following ifcfg file contents:
BOOTPROTO=none BROADCAST=””
DEFROUTE=yes DEVICE=eth1
. . . GATEWAY=X.Y.Z.234
IPADDR=A.B.C.2
IPV4_FAILURE_FATAL=yes NAME=”LAN Link – eth1″
NETMASK=”255.255.255.128″
NETWORK=”A.B.C.0″
NM_CONTROLLED=no ONBOOT=yes PREFIX%
TYPE=Ethernet USERCTL=no
And an aliased ifcfg containing this:
BOOTPROTO=”none”
BROADCAST=”192.168.8.255″
DEVICE=”eth1:192008001″
IPADDR=”192.168.8.1″
IPV6INIT=”no”
NETMASK=”255.255.255.0″
NETWORK=”192.168.8.0″
ONPARENT=”yes”
However, ifconfig shows this:
# ifconfig eth1:192008001
eth1:192008001 Link encap:Ethernet HWaddr 00:25:90:61:74:C1
inet addr:192.168.8.1 Bcast:192.168.8.255
Mask:255.255.255.128
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
Interrupt:17 Memory:feae0000-feb00000
Which shows that the network mask is determined by the interface mask and is not overridden by the alias definition.
Is this expected behaviour? Does this mean that a particular physical interface cannot belong to more than one network, or at least not to networks having differing cidr masks?
2 thoughts on - Netmask On Aliases Overriden By Netmask On Interface
Interface aliases are evil from my point of view. I recommend to configure the ip directly to the interface.
#ifcfg-eth2
[…]
IPADDR2.168.200.1
NETMASK%5.255.255.0
IPADDR22.168.201.1
NETMASK2%5.255.255.192
ip addr show dev eth2 mtu 1500 qdisc pfifo_fast state UP qlen 1000
4: eth2:
link/ether 08:00:27:b0:c5:7c brd ff:ff:ff:ff:ff:ff
inet 192.168.200.1/24 brd 192.168.200.255 scope global eth2
inet 192.168.201.1/26 brd 192.168.201.63 scope global eth2
inet6 fe80::a00:27ff:feb0:c57c/64 scope link
valid_lft forever preferred_lft forever
Best regards Ulf
Just a cautionary note, if you use snmpd you may start seeing regular “ia_addr insert” errors using this approach depending on your version of snmpd and how reporting is configured.
Leroy Tennison Network Information/Cyber Security Specialist E: leroy@datavoiceint.com
2220 Bush Dr McKinney, Texas
75070
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