Brocade TurboIron 24X Series Configuration Guide - Manual (Page 485)

Brocade TurboIron 24X Series Configuration Guide 451
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Configuring IP parameters – Layer 3 Switches
With IPv4, four IP addresses with a 30-bit subnet mask are allocated on point-to-point networks. In
contrast, a 31-bit subnet mask uses only two IP addresses: all zero bits and all one bits in the host
portion of the IP address. The two IP addresses are interpreted as host addresses, and do not
require broadcast support because any packet that is transmitted by one host is always received by
the other host at the receiving end. Therefore, directed broadcast on a point-to-point interface is
eliminated.
IP-directed broadcast CLI configuration at the global level, or the per interface level, is not
applicable on interfaces configured with a 31-bit subnet mask IP address.
When the 31-bit subnet mask address is configured on a point-to-point link, using network
addresses for broadcast purposes is not allowed. For example, in an IPV4 broadcast scheme, the
following subnets can be configured:
• 10.10.10.1 - Subnet for directed broadcast: {, -1}
• 10.10.10.0 - Subnet for network address: {, 0}
In a point-to-point link with a 31-bit subnet mask, the previous two addresses are interpreted as
host addresses and packets are not rebroadcast.
Configuring an IPv4 address with a 31-bit subnet mask
To configure an IPv4 address with a 31-bit subnet mask, enter the following commands.
You can configure an IPv4 address with a 31-bit subnet mask on any interface (for example,
Ethernet, loopback, VE, or tunnel interfaces).
TurboIron(config)#interface ethernet 1/1/5
TurboIron(config-if-e1000-1/5)#ip address 10.9.9.9 255.255.255.254
You can also enter the IP address and mask in the Classless Inter-domain Routing (CIDR) format, as
follows.
TurboIron(config-if-e1000-1/1/5)#ip address 10.9.9.9/31
Syntax: [no] ip address
Syntax: [no] ip address /
The variable specifies the host address. The <ip-mask> variable specifies the IP
network mask. The variable specifies the network prefix mask.
To disable configuration for an IPv4 address with a 31-bit subnet mask on any interface, use the no
form of the command.
You cannot configure a secondary IPv4 address with a 31-bit subnet mask on any interface. The
following error message is displayed when a secondary IPv4 address with a 31-bit subnet mask is
configured.
IP/Port: Errno(10) Cannot assign /31 subnet address as secondary
Configuration example
Figure 56 shows the usage of 31- and 24-bit subnet masks in configuring IP addresses.
FIGURE 56 Configured 31- bit and 24-bit subnet masks