Databases Reference
In-Depth Information
are normally assigned addresses during the boot process as well. Any system has exactly one
boot IP address. To obtain the boot IP address of a UNIX system, you might
ping
the system itself.
$ ping -c 1 `hostname`
PING dbserver1.oradbpro.com (172.168.0.1) 56(84) bytes of data.
64 bytes from dbserver1.oradbpro.com (172.168.0.1): icmp_seq=0 ttl=64 time=0.029 ms
--- dbserver1.oradbpro.com ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.029/0.029/0.029/0.000 ms, pipe 2
On Linux, the switch
-c
instructs
ping
to send a single packet. Use
ping
host_name packet_
size count
with a
count
of 1 on Solaris.
The term
service address
is used to refer to IP addresses that applications use to provide
certain services. Often, service addresses are not assigned to a separate physical network adapter,
but are added as an alias address to a network adapter that already has a boot address or a non-
boot address. This approach is called IP aliasing. A service address is also a non-boot address,
the difference being that the former is assigned to a virtual adapter whereas the latter is assigned to
a physical adapter.
Within a single operating system instance, each network adapter is identified by a unique
name. AIX uses ent
N
, Solaris hme
N
(hme=hundred megabit ethernet) or ge
N
(ge=gigabit
ethernet), whereas Linux uses eth
N
, where
N
is an integer that distinguishes several adapters
of the same type. Additional adapter names are required for use with IP aliasing. The adapter
name for adding the alias IP is formed by adding a colon and a number to the physical adapter's
name. For instance, the physical adapter might be called eth0 and the adapter for IP aliasing
eth0:1. The alias IP address cannot be chosen arbitrarily. It must reside within the same network as
the IP address of the associated physical adapter. The network mask must be taken into consider-
ation too (Mask:255.255.255.0 in the next example). These topics are well beyond the scope of
this topic.
2
Clustering software relocates service addresses from a failed node of a cluster to a surviving
node in the same cluster. Service IP addresses assigned by Oracle10
g
Clusterware are called
virtual IP addresses (VIPs). This is just another term for the same IP aliasing concept. In a RAC
cluster, the VIP of a failing node is assigned to a surviving node. The implementation of virtual
IP addresses uses IP aliasing. IP aliasing can easily be done manually by the UNIX user root
using the command
ifconfig
. Here's an example that adds a service IP address to adapter eth1
on a Linux system:
# ifconfig eth1
eth1 Link encap:Ethernet HWaddr 00:0C:29:07:84:EC
inet addr:172.168.0.1 Bcast:172.168.0.255 Mask:255.255.255.0
inet6 addr: fe80::20c:29ff:fe07:84ec/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
…
# ifconfig eth1:1 inet 172.168.0.11 # IP aliasing on adapter eth1
2.
