有人审核过默认的 OpenWrt 防火墙规则吗？

Question

我从以下位置安装了 Openwrt 10.03.1：openwrt-ar71xx-wrt160nl-squashfs-factory.bin（防火墙仅使用此自定义：sed 's/REJECT/DROP/g' /etc/config/firewall）-除此之外，这是默认的 OPENWRT 安装
我有 3 个 SSID 供 3 个客户使用。这是 WRT160NL。
它通过 pppoe 连接到互联网，因此 pppoe-wan 是 WAN 接口（实际上“eth1”是 WAN 接口，电缆插入该端口）。
所以我把接下来的事情打印在纸上：

iptables-保存

root@OPENWRT:~# iptables-save
# Generated by iptables-save v1.4.6 on Wed Nov 21 16:59:23 2012
*nat
:PREROUTING ACCEPT [282:28098]
:POSTROUTING ACCEPT [12:748]
:OUTPUT ACCEPT [170:12487]
:nat_reflection_in - [0:0]
:nat_reflection_out - [0:0]
:postrouting_rule - [0:0]
:prerouting_lan - [0:0]
:prerouting_rule - [0:0]
:prerouting_wan - [0:0]
:zone_lan_nat - [0:0]
:zone_lan_prerouting - [0:0]
:zone_wan_nat - [0:0]
:zone_wan_prerouting - [0:0]
-A PREROUTING -j prerouting_rule 
-A PREROUTING -i br-lan -j zone_lan_prerouting 
-A PREROUTING -i pppoe-wan -j zone_wan_prerouting 
-A POSTROUTING -j postrouting_rule 
-A POSTROUTING -o br-lan -j zone_lan_nat 
-A POSTROUTING -o pppoe-wan -j zone_wan_nat 
-A postrouting_rule -j nat_reflection_out 
-A prerouting_rule -j nat_reflection_in 
-A zone_lan_prerouting -j prerouting_lan 
-A zone_wan_nat -j MASQUERADE 
-A zone_wan_prerouting -j prerouting_wan 
COMMIT
# Completed on Wed Nov 21 16:59:23 2012
# Generated by iptables-save v1.4.6 on Wed Nov 21 16:59:23 2012
*raw
:PREROUTING ACCEPT [88762:5585776]
:OUTPUT ACCEPT [32677:185865297]
:zone_lan_notrack - [0:0]
:zone_wan_notrack - [0:0]
-A PREROUTING -i br-lan -j zone_lan_notrack 
-A PREROUTING -i pppoe-wan -j zone_wan_notrack 
COMMIT
# Completed on Wed Nov 21 16:59:23 2012
# Generated by iptables-save v1.4.6 on Wed Nov 21 16:59:23 2012
*mangle
:PREROUTING ACCEPT [88762:5585776]
:INPUT ACCEPT [86059:4425898]
:FORWARD ACCEPT [2664:1156339]
:OUTPUT ACCEPT [32677:185865297]
:POSTROUTING ACCEPT [35338:187021465]
:zone_wan_MSSFIX - [0:0]
-A FORWARD -j zone_wan_MSSFIX 
-A zone_wan_MSSFIX -o pppoe-wan -p tcp -m tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp-mss-to-pmtu 
COMMIT
# Completed on Wed Nov 21 16:59:23 2012
# Generated by iptables-save v1.4.6 on Wed Nov 21 16:59:23 2012
*filter
:INPUT DROP [0:0]
:FORWARD DROP [0:0]
:OUTPUT ACCEPT [0:0]
:forward - [0:0]
:forwarding_lan - [0:0]
:forwarding_rule - [0:0]
:forwarding_wan - [0:0]
:input - [0:0]
:input_lan - [0:0]
:input_rule - [0:0]
:input_wan - [0:0]
:nat_reflection_fwd - [0:0]
:output - [0:0]
:output_rule - [0:0]
:reject - [0:0]
:syn_flood - [0:0]
:zone_lan - [0:0]
:zone_lan_ACCEPT - [0:0]
:zone_lan_DROP - [0:0]
:zone_lan_REJECT - [0:0]
:zone_lan_forward - [0:0]
:zone_wan - [0:0]
:zone_wan_ACCEPT - [0:0]
:zone_wan_DROP - [0:0]
:zone_wan_REJECT - [0:0]
:zone_wan_forward - [0:0]
-A INPUT -m state --state INVALID -j DROP 
-A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT 
-A INPUT -i lo -j ACCEPT 
-A INPUT -p tcp -m tcp --tcp-flags FIN,SYN,RST,ACK SYN -j syn_flood 
-A INPUT -j input_rule 
-A INPUT -j input 
-A FORWARD -m state --state INVALID -j DROP 
-A FORWARD -m state --state RELATED,ESTABLISHED -j ACCEPT 
-A FORWARD -j forwarding_rule 
-A FORWARD -j forward 
-A OUTPUT -m state --state INVALID -j DROP 
-A OUTPUT -m state --state RELATED,ESTABLISHED -j ACCEPT 
-A OUTPUT -o lo -j ACCEPT 
-A OUTPUT -j output_rule 
-A OUTPUT -j output 
-A forward -i br-lan -j zone_lan_forward 
-A forward -i pppoe-wan -j zone_wan_forward 
-A forwarding_rule -j nat_reflection_fwd 
-A input -i br-lan -j zone_lan 
-A input -i pppoe-wan -j zone_wan 
-A output -j zone_lan_ACCEPT 
-A output -j zone_wan_ACCEPT 
-A reject -p tcp -j REJECT --reject-with tcp-reset 
-A reject -j REJECT --reject-with icmp-port-unreachable 
-A syn_flood -p tcp -m tcp --tcp-flags FIN,SYN,RST,ACK SYN -m limit --limit 25/sec --limit-burst 50 -j RETURN 
-A syn_flood -j DROP 
-A zone_lan -j input_lan 
-A zone_lan -j zone_lan_ACCEPT 
-A zone_lan_ACCEPT -o br-lan -j ACCEPT 
-A zone_lan_ACCEPT -i br-lan -j ACCEPT 
**-A zone_lan_DROP -o br-lan -j DROP**
**-A zone_lan_DROP -i br-lan -j DROP**
**-A zone_lan_REJECT -o br-lan -j reject**
**-A zone_lan_REJECT -i br-lan -j reject**
-A zone_lan_forward -j zone_wan_ACCEPT 
-A zone_lan_forward -j forwarding_lan 
-A zone_lan_forward -j zone_lan_DROP 
-A zone_wan -p udp -m udp --dport 68 -j ACCEPT 
-A zone_wan -p icmp -m icmp --icmp-type 8 -j DROP 
-A zone_wan -j input_wan 
-A zone_wan -j zone_wan_DROP 
-A zone_wan_ACCEPT -o pppoe-wan -j ACCEPT 
-A zone_wan_ACCEPT -i pppoe-wan -j ACCEPT 
-A zone_wan_DROP -o pppoe-wan -j DROP 
-A zone_wan_DROP -i pppoe-wan -j DROP 
-A zone_wan_REJECT -o pppoe-wan -j reject 
-A zone_wan_REJECT -i pppoe-wan -j reject 
-A zone_wan_forward -j forwarding_wan 
-A zone_wan_forward -j zone_wan_DROP 
COMMIT
# Completed on Wed Nov 21 16:59:23 2012
root@OPENWRT:~# 

如果配置

root@OPENWRT:~# ifconfig
br-lan    Link encap:Ethernet  HWaddr AA:AA:AA:AA:AA:AA
      inet addr:192.168.1.1  Bcast:192.168.1.255  Mask:255.255.255.0
      UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
      RX packets:87174 errors:0 dropped:0 overruns:0 frame:0
      TX packets:137186 errors:0 dropped:0 overruns:0 carrier:0
      collisions:0 txqueuelen:0 
      RX bytes:4532245 (4.3 MiB)  TX bytes:192952659 (184.0 MiB)

eth0      Link encap:Ethernet  HWaddr AA:AA:AA:AA:AA:AA
      UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
      RX packets:0 errors:0 dropped:0 overruns:0 frame:0
      TX packets:16 errors:0 dropped:0 overruns:0 carrier:0
      collisions:0 txqueuelen:1000 
      RX bytes:0 (0.0 B)  TX bytes:2578 (2.5 KiB)
      Interrupt:4 

eth1      Link encap:Ethernet  HWaddr BB:BB:BB:BB:BB:BB
      UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
      RX packets:3661 errors:0 dropped:0 overruns:0 frame:0
      TX packets:3447 errors:0 dropped:0 overruns:0 carrier:0
      collisions:0 txqueuelen:1000 
      RX bytes:1221049 (1.1 MiB)  TX bytes:224533 (219.2 KiB)
      Interrupt:5 

lo        Link encap:Local Loopback  
      inet addr:127.0.0.1  Mask:255.0.0.0
      UP LOOPBACK RUNNING  MTU:16436  Metric:1
      RX packets:24 errors:0 dropped:0 overruns:0 frame:0
      TX packets:24 errors:0 dropped:0 overruns:0 carrier:0
      collisions:0 txqueuelen:0 
      RX bytes:2088 (2.0 KiB)  TX bytes:2088 (2.0 KiB)

mon.wlan0 Link encap:UNSPEC  HWaddr CC-CC-CC-CC-CC-C1-00-00-00-00-00-00-00-00-00-00  
      UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
      RX packets:263 errors:0 dropped:0 overruns:0 frame:0
      TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
      collisions:0 txqueuelen:32 
      RX bytes:20929 (20.4 KiB)  TX bytes:0 (0.0 B)

pppoe-wan Link encap:Point-to-Point Protocol  
      inet addr:1.2.3.4  P-t-P:10.0.0.1  Mask:255.255.255.255
      UP POINTOPOINT RUNNING NOARP MULTICAST  MTU:1492  Metric:1
      RX packets:1646 errors:0 dropped:0 overruns:0 frame:0
      TX packets:1448 errors:0 dropped:0 overruns:0 carrier:0
      collisions:0 txqueuelen:3 
      RX bytes:1063783 (1.0 MiB)  TX bytes:132628 (129.5 KiB)

wlan0     Link encap:Ethernet  HWaddr CC:CC:CC:CC:CC:C1
      UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
      RX packets:0 errors:0 dropped:0 overruns:0 frame:0
      TX packets:16 errors:0 dropped:0 overruns:0 carrier:0
      collisions:0 txqueuelen:32 
      RX bytes:0 (0.0 B)  TX bytes:2850 (2.7 KiB)

wlan0-1   Link encap:Ethernet  HWaddr CC:CC:CC:CC:CC:C2
      UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
      RX packets:0 errors:0 dropped:0 overruns:0 frame:0
      TX packets:16 errors:0 dropped:0 overruns:0 carrier:0
      collisions:0 txqueuelen:32 
      RX bytes:0 (0.0 B)  TX bytes:2850 (2.7 KiB)

wlan0-2   Link encap:Ethernet  HWaddr CC:CC:CC:CC:CC:C3
      UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
      RX packets:0 errors:0 dropped:0 overruns:0 frame:0
      TX packets:16 errors:0 dropped:0 overruns:0 carrier:0
      collisions:0 txqueuelen:32 
      RX bytes:0 (0.0 B)  TX bytes:2850 (2.7 KiB)

brctl 显示

root@OPENWRT:~# brctl show
bridge name bridge id       STP enabled interfaces
br-lan      8000.129ce121c98e   no      eth0
                            wlan0
                            wlan0-1
                            wlan0-2
root@OPENWRT:~# 

...并仔细观察它几次。我发现了一些我不明白的事情：

1）
这些规则完全没有用，我很确定，所以对此没有真正的问题，至少是“修复”。
-A zone_lan_DROP -o br-lan -j DROP
-A zone_lan_DROP -i br-lan -j DROP
-A zone_lan_REJECT -o br-lan -j reject
-A zone_lan_REJECT -i br-lan -j reject

2)
真正的问题是......为什么有这么多桌子？
nat_reflection_in, nat_reflection_out, postrouting_rule, prerouting_lan, prerouting_rule, prerouting_wan, zone_lan_nat, zone_lan_prerouting, zone_wan_nat, zone_wan_prerouting, zone_lan, zone_lan_forward, zone_wan, zone_wan_forward等
没有桌子就不能制定规则吗？OpenWrt 路由器通常 CPU 很小，为什么要使用复杂的规则？为什么不更简单？没有桌子？

3）
......如果没有人能提出一个好的答案，为什么需要这些表......那么afaik我将刷新所有规则等，并手工完成......以更简单的方式道路..

Answer 1

1）这些规则完全无用，我确信这一点，所以对此没有真正的问题，至少是“修复”。

不，这些规则很有用。如果你告诉我为什么你认为它们没用，我会告诉你为什么。

好吧，我开玩笑的，我会告诉你你是否想要。这些规则的目的是保持设计简单。简单性不是用规则的数量来衡量的。这些规则是有方法的。每个表都有一个简单易懂的目的，这在其名称中是显而易见的。碰巧在默认配置中，某些表只有一个规则。它需要在 OpenWRT 中使用更复杂的代码来优化单规则表。这也会使系统管理员更难在不通过这个假设的编译器的情况下调整规则。

2）真正的问题是……为什么有这么多桌子？

这些表对应于 OpenWRT 防火墙设置的功能。您可以拥有更少的规则，但这样您就会失去对某些用户有用的功能。

没有桌子就不能制定规则吗？OpenWrt 路由器通常 CPU 很小，为什么要使用复杂的规则？为什么不更简单？没有桌子？

毫无疑问，您可以使用更少的表进行自己的配置（除非您的防火墙非常简单，否则您最终可能会创建一些）。OpenWRT 更加灵活，因为它可以容纳许多用户。

规则的数量与 CPU 速度或 RAM 大小无关。表数量的影响与通过它们所花费的时间几乎不相关——相反，拥有更多的表和每张表的规则更少意味着每个数据包通过的路径会更短（拥有更宽的树有助于让它不那么深）。对内存的影响可以忽略不计：每个表几百字节 vs 几兆字节 RAM。