Centos 系列修改资料网上比较多，freebsd 增加ip也很多，MTU比较少。
主要是修改这两条。ifconfig_re0_alias0 是增加的别名
原IP  119.252.248.25
添加新ip 119.252.248.84

ifconfig_re0="inet 119.252.248.25  netmask 255.255.255.0 mtu 1420"
ifconfig_re0_alias0="inet 119.252.248.84 netmask 255.255.255.128 mtu 1420"

修改完后录入 之后 reboot 或 #sh /etc/rc

/etc/rc.conf

m176net# vi /etc/rc.conf

# -- sysinstall generated deltas -- # Mon Nov 12 17:55:22 2012
# Created: Mon Nov 12 17:55:22 2012
# Enable network daemons for user convenience.
# Please make all changes to this file, not to /etc/defaults/rc.conf.
# This file now contains just the overrides from /etc/defaults/rc.conf.
defaultrouter="119.252.248.2"
gateway_enable="YES"
hostname="m176net"
ifconfig_re0="inet 119.252.248.25  netmask 255.255.255.0 mtu 1420"
ifconfig_re0_alias0="inet 119.252.249.84 netmask 255.255.255.128 mtu 1420"
inetd_enable="YES"
sshd_enable="YES"
~

~
~