http://www.technomenace.com/2009/06/implement-bonding-rhel-5/
Bonding is the process of combining 2 NICs on a system into a single device. For e.g., if you have 2 network cards on a machine, eth0 and eth1, you combine the same into a bond device, bond0 and then configure an IP for this bond device.
Why do we have to do that, you may ask. In the case that I mentioned, if I configure bond0 as 192.168.1.5, both eth0 and eth1 can send or receive packets that are meant for bond device IP(192.168.1.5). Its like you now have 2 paths to reach a destination. Bond devices can be configured in different modes which can be utilized to provide fault tolerance, greater performance or both, depending on the mode.
Bonding is talked about in greater detail in/usr/share/doc/kernel-doc-/Documentation/networking/bonding.txt.
As usual, all my experiments are on either Xen or VMWare guests and this one is no different. The below steps successfully worked for me on a RHEL 5.3 Xen guest. To start with, eth0 was configured as 192.168.122.118 while eth1 remained unassigned. I am about to create a bond device bond0 with eth0 and eth1, and assign this IP into it.
1. Add the below lines to /etc/modprobe.conf
alias bond0 bonding
options bond0 mode=1 miimon=100
We are loading the bonding kernel module required to make this work, along with some options. mode=1 means that I have opted for active-backup setup. Here, only one slave in the bond device will be active at the moment. If the active slave goes down, the other slave becomes active and all traffic is then done via the newly active slave. If this sounds a bit confusing, just read on. Also, the value of miimon specifies how often MII link monitoring occurs. For a complete list of all the available arguments, feel free to check the kernel documentation.
2. Create bond0 device file, /etc/sysconfig/network-scripts/ifcfg-bond0 with the following content:
DEVICE=bond0
BOOTPROTO=none
ONBOOT=yes
NETWORK=192.168.122.0
NETMASK=255.255.255.0
IPADDR=192.168.122.118
USERCTL=no
The lines are self-explanatory, defining the device name and then specifying its IP address, netmask and all.
3. Create /etc/sysconfig/network-scripts/ifcfg-eth0 with content:
DEVICE=eth0
MASTER=bond0
SLAVE=yes
USERCTL=no
BOOTPROTO=dhcp
IPV6INIT=yes
IPV6_AUTOCONF=yes
ONBOOT=yes
4. Create /etc/sysconfig/network-scripts/ifcfg-eth1 with content:
DEVICE=eth1
MASTER=bond0
SLAVE=yes
USERCTL=no
BOOTPROTO=dhcp
IPV6INIT=yes
IPV6_AUTOCONF=yes
ONBOOT=yes
The important lines here to note are “MASTER=bond0“, and “SLAVE=yes” which tells that both eth0 and eth1 are now part of bond0 device.
5. Restart network and you are done!
[root@localhost ~]# service network restart
Shutting down interface eth0:
[OK]
Shutting down loopback interface:
[OK]
Bringing up loopback interface:
[OK]
Bringing up interface bond0:
[OK]
[root@localhost ~]# ifconfig
bond0 Link encap:EthernetHWaddr 00:16:3E:1C:C5:A7
inet addr:192.168.122.118Bcast:192.168.122.255Mask:255.255.255.0
inet6 addr: fe80::216:3eff:fe1c:c5a7/64 Scope:Link
UP BROADCAST RUNNING MASTER MULTICASTMTU:1500Metric:1
RX packets:80 errors:0 dropped:0 overruns:0 frame:0
TX packets:54 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:11210 (10.9 KiB)TX bytes:11630 (11.3 KiB)
eth0Link encap:EthernetHWaddr 00:16:3E:1C:C5:A7
UP BROADCAST RUNNING SLAVE MULTICASTMTU:1500Metric:1
RX packets:45 errors:0 dropped:0 overruns:0 frame:0
TX packets:63 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:3288 (3.2 KiB)TX bytes:13120 (12.8 KiB)
eth1Link encap:EthernetHWaddr 00:16:3E:1C:C5:A7
UP BROADCAST RUNNING SLAVE MULTICASTMTU:1500Metric:1
RX packets:42 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:8384 (8.1 KiB)TX bytes:0 (0.0 b)
loLink encap:Local Loopback
inet addr:127.0.0.1Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNINGMTU:16436Metric:1
RX packets:10 errors:0 dropped:0 overruns:0 frame:0
TX packets:10 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:764 (764.0 b)TX bytes:764 (764.0 b)
As you can see from the output of ifconfig, device bond0 is listed as MASTER while devices eth0 and eth1 are listed as SLAVE. Also, the hardware address of bond0 and its underlying devices eth0 and eth1 are the same (00:16:3E:1C:C5:A7). In case you have multiple bond devices, comparing the hardware address of that bond device with the actual network device (ethX) will tell you whether it is a part of that particular bonding or not.
Now, the current status of the bond device bond0 is present in /proc/net/bonding/bond0. Time to fool around with bonding now…
[root@localhost ~]# cat /proc/net/bonding/bond0
Ethernet Channel Bonding Driver: v3.2.4 (January 28, 2008)
Bonding Mode: fault-tolerance (active-backup)
Primary Slave: None
Currently Active Slave: eth0
MII Status: up
MII Polling Interval (ms): 100
Up Delay (ms): 0
Down Delay (ms): 0
Slave Interface: eth0
MII Status: up
Link Failure Count: 0
Permanent HW addr: 00:16:3e:1c:c5:a7
Slave Interface: eth1
MII Status: up
Link Failure Count: 0
Permanent HW addr: 00:16:3e:58:02:c7
As I have highlighted above, the bonding mode is active-passive (since I used mode=1 to configure it in modprobe.conf). Also, both interfaces are up, but current active slave is eth0. Now, what happens when I down eth0? Normally when we down an interface, the IP associated with it also goes down (becomes unreachable). However, in bonding, it just switches over to next slave, eth1 - keeping the connection and the IP active:
[root@localhost ~]# ifdown eth0
[root@localhost ~]# cat /proc/net/bonding/bond0
Ethernet Channel Bonding Driver: v3.2.4 (January 28, 2008)
Bonding Mode: fault-tolerance (active-backup)
Primary Slave: None
Currently Active Slave: eth1
MII Status: up
MII Polling Interval (ms): 100
Up Delay (ms): 0
Down Delay (ms): 0
Slave Interface: eth1
MII Status: up
Link Failure Count: 0
Permanent HW addr: 00:16:3e:58:02:c7
[root@localhost ~]# ifup eth0
[root@localhost ~]# cat /proc/net/bonding/bond0
Ethernet Channel Bonding Driver: v3.2.4 (January 28, 2008)
Bonding Mode: fault-tolerance (active-backup)
Primary Slave: None
Currently Active Slave: eth1
MII Status: up
MII Polling Interval (ms): 100
Up Delay (ms): 0
Down Delay (ms): 0
Slave Interface: eth1
MII Status: up
Link Failure Count: 0
Permanent HW addr: 00:16:3e:58:02:c7
Slave Interface: eth0
MII Status: up
Link Failure Count: 0
Permanent HW addr: 00:16:3e:1c:c5:a7
Notice that when I started eth0 again (ifup eth0), it got added to the bond device automatically. Also, in the above output, even though the permanent HW Address of eth0 and eth1 are different, they retain the HW address of the bond device in ifconfig output:
[root@localhost ~]# ifconfig
bond0 Link encap:EthernetHWaddr 00:16:3E:1C:C5:A7
inet addr:192.168.122.118Bcast:192.168.122.255Mask:255.255.255.0
inet6 addr: fe80::216:3eff:fe1c:c5a7/64 Scope:Link
UP BROADCAST RUNNING MASTER MULTICASTMTU:1500Metric:1
RX packets:87 errors:0 dropped:0 overruns:0 frame:0
TX packets:35 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:6340 (6.1 KiB)TX bytes:4950 (4.8 KiB)
eth0Link encap:EthernetHWaddr 00:16:3E:1C:C5:A7
UP BROADCAST RUNNING SLAVE MULTICASTMTU:1500Metric:1
RX packets:85 errors:0 dropped:0 overruns:0 frame:0
TX packets:44 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:6360 (6.2 KiB)TX bytes:6424 (6.2 KiB)
eth1Link encap:EthernetHWaddr 00:16:3E:1C:C5:A7
UP BROADCAST RUNNING SLAVE MULTICASTMTU:1500Metric:1
RX packets:11 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:574 (574.0 b)TX bytes:0 (0.0 b)
loLink encap:Local Loopback
inet addr:127.0.0.1Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNINGMTU:16436Metric:1
RX packets:10 errors:0 dropped:0 overruns:0 frame:0
TX packets:10 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:764 (764.0 b)TX bytes:764 (764.0 b)
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