Database Reference
In-Depth Information
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as the cluster interconnect details are stored in oCr and profile.xml file, changing network interfaces or ip
addresses for private network from 11g needs to be carefully coordinated. You need to add new ip addresses and
interfaces while the Clusterware is up and running using the oifcfg command. the oifcfg command updates both oCr
and the profile.xml correctly. then, shut down the Clusterware, make the changes in the network side, and restart the
Clusterware. Drop the old interfaces after verifying that Clusterware is working fine and restart Clusterware again. Due to
the complexity of the steps involved, you should probably verify the sequence of steps with oracle support.
Note
To sum up, a private network should be configured with non-routable IP addresses, and multiple network
interfaces in different subnets should possibly be configured so that you can avoid any single point of failure.
Jumbo Frames
Maximum Transmission Unit (MTU) defines the size of largest data unit that can be handled by a protocol layer,
a network interface, or a network switch.
1.
Default MTU for a network interface is 1,500 bytes. Size of Ethernet frames is 1,518 bytes
on the wire.
2.
Out of 1,518 bytes in a frame, 14 bytes are reserved for Ethernet header and 4 bytes
reserved for Ethernet CRC, leaving 1,500 bytes available for higher-level protocol (TCP,
UDP, etc.) payload.
3.
For IPv4, a maximum payload of 1,460 bytes for TCP and a maximum payload of 1,476 for
UDP are allowed.
4.
For IPv6, a maximum payload of 1,440 bytes for TCP and a maximum payload of 1,456 for
UDP are allowed. Again, IPv6 is not allowed for private network (including 12c). Jumbo
Frame setup applies mostly to private network traffic, and so there is no reason to discuss
IPv6 Jumbo Frame setup here.
5.
Path MTU
defines the size of the largest data unit that can flow through a path between
a source and a target. In a RAC cluster, typically, a router/switch connects cluster nodes,
and the maximum MTU that can be handled by the switch also plays a role in deciding
path MTU.
For example, the following ifconfig command output shows an MTU of 1,500 bytes for eth3 logical interface.
The size of a packet that flowing through this interface cannot exceed 1,500 bytes.
$ifconfig -a |more
...
eth3:1: ...<UP,BROADCAST,RUNNING,MULTICAST,IPv4 >
mtu 1500
index 4
inet 169.254.28.111 netmask ffffc000 broadcast 169.254.63.255
...
With a configured MTU of ~1,500 bytes in the path, transfer of a data block of size 8K from one node to another
node requires six IP packets to be transmitted. An 8K buffer is fragmented into six IP packets and sent to the receiving
side. On the receiving side, these six IP packets are received and reassembled to recreate the 8K buffer. The reassembled
buffer is finally passed to the application for further processing.
