Database Reference
In-Depth Information
# ifconfig eth1:1
eth1:1 Link encap:Ethernet HWaddr 00:0C:29:07:84:EC
inet addr:172.168.0.11 Bcast:172.168.255.255 Mask:255.255.0.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
Interrupt:169 Base address:0x2080
# ping -c 1 172.168.0.11
PING 172.168.0.11 (172.168.0.11) 56(84) bytes of data.
64 bytes from 172.168.0.11: icmp_seq=0 ttl=64 time=0.072 ms
--- 172.168.0.11 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.072/0.072/0.072/0.000 ms, pipe 2
Multihomed Systems
Systems where ORACLE database software is installed may have more than a single network
interface controller (NIC). A machine might belong to different LAN segments or it might have
a separate network adapter for backup and restore traffic. Clustered systems running Real
Application Clusters (RAC) have a separate private network called
interconnect
for communi-
cation between individual RAC DBMS instances. Machines with several network interface
controllers (a.k.a. network adapters) are sometimes referred to as
multihomed
, since they are
“at home” in more than just one network. If only we as humans were as fortunate as computer
systems and did not have to pay an extra rent for multiple homes.
The term multihomed is somewhat ambiguous. It may be used in a broad sense where it
describes any machine that has several network adapters connected to one or more networks,
or in a narrow sense where it only applies to Internet access via more than a single network for
higher reliability.
3
It may be the intention of a network administrator to allow clients on a certain LAN segment
access to a DBMS instance on a multihomed system, but deny access to clients on another LAN
segment. To achieve this, the DBA needs to make sure that the TNS Listener can be reached
from one LAN segment but not the other. Technically speaking, the TNS Listener should bind
to the IP address of one adapter, but not the other.
Now it's time to finally fill you in on the rather awkward acronym
INADDR_ANY
, that was
mentioned in the status section at the beginning of this chapter. It is a C language preprocessor
macro used in the C language programming interface for sockets. On POSIX-compliant systems,
TCP/IP as well as UDP networking is implemented using sockets (see
man
socket
). The socket
programming paradigm for a server process such as the TNS Listener is to
1.
create a socket
bind the socket to an address, potentially using
INADDR_ANY
2.
3.
listen for incoming connections
4.
accept incoming connections (or maybe not as in valid node checking discussed in
Chapter 30)
3.
