关于RHEL6.3 sysctl 一个错误问题的解决

笔者在RHEL6.3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
kernel.shmmax = 68719476736
kernel.shmall = 4294967296

经过Google大神点击打开链接后来找到的了原因所在，原来以下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

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
# 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
net.bridge.bridge-nf-call-ip6tables = 0
net.bridge.bridge-nf-call-iptables = 0
net.bridge.bridge-nf-call-arptables = 0
kernel.msgmnb = 65536
kernel.msgmax = 65536
kernel.shmmax = 68719476736
kernel.shmall = 4294967296

有人可能会好奇这三个值得意义所在，我在红帽官网找到了相关说明 点击打开链接

以下大致的意思主要说使用以上3个选项阻止桥接流量获得通过主机iptables规则，Netfilter是默认情况下启用了桥梁，如果不阻止会导致严重的混乱

netfilter is currently enabled on bridges by default. This means, for example, that IP packets that are forwarded across the bridge are filtered by the iptables FORWARD rules.

In practice, this can lead to serious confusion where someone creates a bridge and finds that some traffic isn't being forwarded across the bridge. Because it's so unexpected that IP firewall rules apply to frames on a bridge, it can take quite some time to figure out what's going on.

The libvirt wiki has this advice:

  http://wiki.libvirt.org/page/Networking#Fedora.2FRHEL_Bridging

  The final step is to configure iptables to allow all traffic to be forwarded 
  across the bridge

  # echo "-I FORWARD -m physdev --physdev-is-bridged -j ACCEPT" > \
       /etc/sysconfig/iptables-forward-bridged
  # lokkit --custom-rules=ipv4:filter:/etc/sysconfig/iptables-forward-bridged
  # service libvirtd reload

  Alternatively, you can prevent bridged traffic getting pushed through the 
  host's iptables rules. In /etc/sysctl.conf add

  # cat >> /etc/sysctl.conf <