NotesByLex

Red Hat System Administration III - Unit 7 - Advanced Network Configuration

Lex Toumbourou ·

Linux

IP Aliasing

  • Assign more than one IP address to an interface
    • Unsupported by DHCP

  • Can add with ip addr command:

    > ip addr show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
    inet6 ::1/128 scope host
      valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether 52:54:00:00:00:02 brd ff:ff:ff:ff:ff:ff
    inet 192.168.0.102/24 brd 192.168.0.255 scope global eth0
    inet6 fe80::5054:ff:fe00:2/64 scope link
      valid_lft forever preferred_lft forever
> ip addr add 1.1.1.1/24 dev eth0 label eth0:0
> ip addr show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
    inet6 ::1/128 scope host
      valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether 52:54:00:00:00:02 brd ff:ff:ff:ff:ff:ff
    inet 192.168.0.102/24 brd 192.168.0.255 scope global eth0
    inet 1.1.1.1/24 scope global eth0:0
    inet6 fe80::5054:ff:fe00:2/64 scope link
      valid_lft forever preferred_lft foreve

  • To make it persistant, add a file /etc/sysconfig/network-scripts/ifcfg-eth0:0

    > service NetworkManager stop; chkconfig NetworkManager off
> cat /etc/sysconfig/network-scripts/ifcfg-eth0:0
DEVICE=eth0:0
IPADDR=1.1.1.1
PREFIX=24
ONPARENT=yes

Bonding

  • To use it, make sure NetworkManager is off.
  • Bonding modes:
    • Mode 0 (balance-rr) - round robin policy; all interfaces are used. Any slave can receive
    • Mode 1 (active-backup) - fault tolerant. Only one slave interface can be used at a time
    • Mode 3 (broadcast) - fault tolerant. All packets are broadcast from the slave interfaces

  • Bonding config is stored in: /etc/sysconfig/network-scripts/ifcfg-bond0

    DEVICE=bond0
IPADDR=1.1.1.1
PREFIX=24
ONBOOT=yes
BOOTPROTO=none
USERCTL=no
BONDING_OPTS="mode=1 miimon=50" # Lower miimon, the more checks to the interfaces

  • Slave config looks like:

    > cat /etc/sysconfig/network-scripts/ifcfg-<name>
DEVICE=<name>
BOOTPROTO=none
ONBOOT=yes
MASTER=bond0
SLAVE=yes
USERCTL=no

  • Create an alias for every bond

    > cat /etc/modprobe.d/bonding.conf
alias bond0 bonding

  • Query state of bonding interface and its slaves using (virtual) file /proc/net/bonding/<interface>

Tuning Kernel Network Parameters

  • sysctl options are as follows:
    • -a - list all available params
    • -w - change a sysctl setting
    • -p - load in sysctl settings from file

  • To setup kernel for packet forwarding:

    > vi /etc/sysctl.conf
+ net.ipv4.ip_forward = 1

  • To setup kernel to respond to ICMP broadcase

    > sysctl -w net.ipv4.icmp_echo_ignore_all=0
> vi /etc/sysctl.conf
+ net.ipv4.icmp_echo_ignore_all = 0

  • To view routes (inc default gateway)

    > ip route show
192.168.0.0/24 dev br0  proto kernel  scope link  src 192.168.0.2
192.168.122.0/24 dev virbr0  proto kernel  scope link  src 192.168.122.1
169.254.0.0/16 dev br0  scope link  metric 1004
default via 192.168.0.254 dev br0

  • Add routes with ip route add network/netmask via router_ip [dev <interface>]

  • Edit route file with /etc/sysconfig/network-scripts/route-iface with these 3 lines:

    ADDRESSX=network
NETMASKX=netmask
GATEWAYX=router_ip

  • ping uses ICMP to send a request and receives a reply