James B. Byrne
2019-Feb-08 14:08 UTC
[CentOS] 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=25
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?
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Ulf Volmer
2019-Feb-08 17:48 UTC
[CentOS] netmask on aliases overriden by netmask on interface
On 08.02.19 15:08, James B. Byrne via CentOS wrote:> # 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?Interface aliases are evil from my point of view. I recommend to configure the ip directly to the interface. #ifcfg-eth2 [...] IPADDR=192.168.200.1 NETMASK=255.255.255.0 IPADDR2=192.168.201.1 NETMASK2=255.255.255.192 ip addr show dev eth2 4: eth2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000 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
Leroy Tennison
2019-Feb-08 18:30 UTC
[CentOS] netmask on aliases overriden by netmask on interface
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 at datavoiceint.com 2220 Bush Dr McKinney, Texas 75070 www.datavoiceint.com This message has been sent on behalf of a company that is part of the Harris Operating Group of Constellation Software Inc. These companies are listed here . If you prefer not to be contacted by Harris Operating Group please notify us . This message is intended exclusively for the individual or entity to which it is addressed. This communication may contain information that is proprietary, privileged or confidential or otherwise legally exempt from disclosure. If you are not the named addressee, you are not authorized to read, print, retain, copy or disseminate this message or any part of it. If you have received this message in error, please notify the sender immediately by e-mail and delete all copies of the message. ________________________________________ From: CentOS <centos-bounces at centos.org> on behalf of Ulf Volmer <u.volmer at u-v.de> Sent: Friday, February 8, 2019 11:48 AM To: centos at centos.org Subject: [EXTERNAL] Re: [CentOS] netmask on aliases overriden by netmask on interface On 08.02.19 15:08, James B. Byrne via CentOS wrote:> # 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?Interface aliases are evil from my point of view. I recommend to configure the ip directly to the interface. #ifcfg-eth2 [...] IPADDR=192.168.200.1 NETMASK=255.255.255.0 IPADDR2=192.168.201.1 NETMASK2=255.255.255.192 ip addr show dev eth2 4: eth2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000 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 _______________________________________________ CentOS mailing list CentOS at centos.org https://lists.centos.org/mailman/listinfo/centos