Networking

Subnet Cheat Sheet

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Subnet Mask Cheat Sheet

Posted here because 95% of the networks are the same and when I encounter a different one I have to think about it…not any more!

See RFC 1878 for more details & information.

Addresses Hosts Netmask Amount of a Class C
/30 4 2 255.255.255.252 1/64
/29 8 6 255.255.255.248 1/32
/28 16 14 255.255.255.240 1/16
/27 32 30 255.255.255.224 1/8
/26 64 62 255.255.255.192 1/4
/25 128 126 255.255.255.128 1/2
/24 256 254 255.255.255.0 1
/23 512 510 255.255.254.0 2
/22 1024 1022 255.255.252.0 4
/21 2048 2046 255.255.248.0 8
/20 4096 4094 255.255.240.0 16
/19 8192 8190 255.255.224.0 32
/18 16384 16382 255.255.192.0 64
/17 32768 32766 255.255.128.0 128
/16 65536 65534 255.255.0.0 256

Network Interface Name in rhel7

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Anyone who has installed rhel7 knows how annoying it is to check you network and not see eth0.  Perhaps it is just me then…  Regardless here are instructions on how to change it:

First you need to know the name of the network adapter in use, you can look in /etc/sysconfig/network-scripts/ifcfg-eno##### or run this command:

# ip addr show
Now you need to do the following:
vim /etc/sysconfig/grub
add “net.ifnames=0 biosdevname=0″ to the end of the line beginning with: GRUB_CMDLINE_LINUX, for example:
GRUB_CMDLINE_LINUX="crashkernel=auto rd.lvm.lv=rhel/root rd.lvm.lv=rhel/swap rhgb quiet net.ifnames=0 biosdevname=0"
Now you need to regenerate the GRUB configuration with the updated kernel parameters:
# grub2-mkconfig -o /boot/grub2/grub.cfg
Now you need to change the ‘eno##” named network scripts you identified above:
# cp -p /etc/sysconfig/network-scripts/ifcfg-eno16780032 /etc/sysconfig/network-scripts/ifcfg-eth0

Next edit the newly copied network script to change any reference to the eno### to eth0, for example:

sed -i -e 's/eno16780032/eth0/g' /etc/sysconfig/network-scripts/ifcfg-eth0

Now reboot:

# shutdown -r now

After system reboot your network interface shall be called eth0 and all will be right in the world again…

Hat tip to Angelo for most of the leg work.