我在RHEL6.2中执行sysctl -p的时候发现输出出现以下错误：
# sysctl -p
net.ipv4.ip_forward = 0
net.ipv4.conf.default.rp_filter = 1
net.ipv4.conf.default.accept_source_route = 0
kernel.sysrq = 0
kernel.core_uses_pid = 1
net.ipv4.tcp_syncookies = 1
error: "net.bridge.bridge-nf-call-ip6tables" is an unknown key
error: "net.bridge.bridge-nf-call-iptables" is an unknown key
error: "net.bridge.bridge-nf-call-arptables" is an unknown key
kernel.msgmnb = 65536
kernel.msgmax = 65536
fs.file-max = 6815744
fs.aio-max-nr = 1048576
kernel.shmall = 2097152
kernel.shmmax = 536870912
kernel.shmmni = 4096
kernel.sem = 250 32000 100 128
net.ipv4.ip_local_port_range = 9000 65500
net.core.rmem_default = 262144
net.core.rmem_max = 4194304
net.core.wmem_default = 262144
net.core.wmem_max = 1048576
在网上找的资料都是说以下3个参数依赖于bridge模块，该模块如果没有加载则会现上面的输出错误（当我们安装bridge-util后，会发现/etc/sysctl.conf中添加了与防火墙相关的参数。但是当我们执行sysctl -p时，报错说key未知。这是因为我们没有加载bridge模块，需要手工加载。）
error: "net.bridge.bridge-nf-call-ip6tables" is an unknown key
error: "net.bridge.bridge-nf-call-iptables" is an unknown key
error: "net.bridge.bridge-nf-call-arptables" is an unknown key
加载模块测试，发现问题解决
# modprobe bridge
#lsmod |grep bridge //查看模块加载
bridge 79790 0
stp 2173 1 bridge
llc 5642 2 bridge,stp
# sysctl -p
net.ipv4.ip_forward = 0
net.ipv4.conf.default.rp_filter = 1
net.ipv4.conf.default.accept_source_route = 0
kernel.sysrq = 0
kernel.core_uses_pid = 1
net.ipv4.tcp_syncookies = 1
kernel.msgmnb = 65536
kernel.msgmax = 65536
fs.file-max = 6815744
fs.aio-max-nr = 1048576
kernel.shmall = 2097152
kernel.shmmax = 536870912
kernel.shmmni = 4096
kernel.sem = 250 32000 100 128
net.ipv4.ip_local_port_range = 9000 65500
net.core.rmem_default = 262144
net.core.rmem_max = 4194304
net.core.wmem_default = 262144
net.core.wmem_max = 1048576
echo "modprobe bridge" >> /etc/rc.local
