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IBM AIX/UNIX system storage administration ksh/perl scripting

Monday, March 16, 2009

Why you should NOT put two interfaces in same subnet

There are couple of reasons as an AIX system administrator you should NOT configure IP addresses that are in the same subnet in different interfaces.

1.Having two interfaces on the same network is a violation of TCP/IP
In TCP/IP architecture, a host machine with two network adapters is
defined as an IP router. Differentnetwork adapters must be attached
to different physical networks. In the case of token-ring, TCP/IP
addresses multiple rings bridged together as a single logical ring
(as if it were a single physical ring).

2.Having two interfaces on the same network can cause broadcast storms.

Whenever an IP host sees traffic for a network whose IP address is diffe
rent from its own network, it generates an Internet Control Message
Protocol (ICMP) packet announcing this conflict. Since every host
on the network sees the traffic that is misaddressed, every host
generates ICMP Packets. If the amount of misaddressed traffic is signif
the ICMP traffic can grow to the point that network performance degrades

3 Having two interfaces on the same network can cause routing confusion.

If system has two interfaces on same subnet, inbound traffic will
from either interface, but for outbound traffic you need to set up
specific routes to use both otherwiese system will use one of them.

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