图1
一、得到某网址与IP地址的对应关系
比如要封www.ttsou.cn，有两种方法可以得到该网址对应的IP地址，第一是ping该网址，如下所示：
C:\>ping www.ttsou.cnPinging www.ttsou.cn [58.61.155.44] with 32 bytes of data:Reply from 58.61.155.44: bytes=32 time=80ms TTL=116Reply from 58.61.155.44: bytes=32 time=78ms TTL=116Reply from 58.61.155.44: bytes=32 time=92ms TTL=116Reply from 58.61.155.44: bytes=32 time=85ms TTL=116Ping statistics for 58.61.155.44:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),Approximate round trip times in milli-seconds:Minimum = 78ms, Maximum = 92ms, Average = 83ms
从中我们可以得到www.ttsou.cn对应的IP地址为58.61.155.44.但是这种方法存在一个缺陷，即如果该网址对应有多个IP地址的话，用ping的方法不可能得到所有对应的IP地址，我们可以用nslookup来解决，如下所示：
C:\>nslookupDefault Server:
ns.jncatv.netAddress:
222.175.169.91> www.ttsou.cnServer:
ns.jncatv.netAddress:
222.175.169.91Non-authoritative answer:Name:
www.ttsou.cnAddress:
58.61.155.44> www.sina.com.cnServer:
ns.jncatv.netAddress:
222.175.169.91Non-authoritative answer:Name:
hydra.sina.com.cnAddresses:
218.30.108.58, 218.30.108.59, 218.30.108.61, 218.30.108.62
218.30.108.64, 218.30.108.65, 218.30.108.66, 218.30.108.67, 218.30.108.68
218.30.108.69, 218.30.108.72, 218.30.108.73, 218.30.108.74, 218.30.108.55
218.30.108.56, 218.30.108.57Aliases:
www.sina.com.cn, jupiter.sina.com.cn
从以上的结果我们可以看出，www.ttsou.cn确实是只对应了一个IP地址，但是象www.sina.com.cn这样的网址就对应了大量的IP地址。
二、在PIX520防火墙上了解当前访问列表的使用情况。
由于我们在PIX520防火墙上作了限制TELNET访问的限制，只有192.168的网段可以通过TELNET的方式登录上去，所以我们要先登录3层交换机（192.168.3.1），再从3层交换机上登录过去，先看一下当前配置：
telnet 192.168.201.1Trying 192.168.201.1 ... OpenUser Access VerificationPassword:Type help or '?' for a list of available commands.pixfirewall> enPassword: ******pixfirewall# show run: Saved:PIX Version 6.2(2)nameif ethernet0 outside security0nameif ethernet1 inside security100
（以下省略）
出于安全方面的考虑，PIX防火墙的具体配置我就不列出了，把与本文有关的内容列出，重点应该看以下两条：
access-group acl_inside in interface outsideaccess-group acl_inside in interface inside
即当前应用的访问列表为acl_inside，然后再看acl_inside是如何写的：
access-list acl_inside deny udp any any eq tftpaccess-list acl_inside deny tcp any any eq 135access-list acl_inside deny udp any any eq 135access-list acl_inside deny tcp any any eq 137access-list acl_inside deny udp any any eq netbios-nsaccess-list acl_inside deny tcp any any eq 138access-list acl_inside deny udp any any eq netbios-dgmaccess-list acl_inside deny tcp any any eq netbios-ssnaccess-list acl_inside deny udp any any eq 139access-list acl_inside deny tcp any any eq 445access-list acl_inside deny tcp any any eq 593access-list acl_inside deny tcp any any eq 4444access-list acl_inside permit ip any anyaccess-list acl_inside permit tcp any any eq 1723access-list acl_inside permit gre any any
从中我们可以看到原访问列表只是对某些端口的使用做了限制，而不涉及对某个IP地址进行访问的限制，为了稳妥起见，我们要先清楚的了解访问列表的格式，如下：
pixfirewall(config)# access-list ?Usage: [no] access-list compiled[no] access-list compiled[no] access-list deny|permit |object-group | object-group
三、具体的操作步骤
为了保障在添加一条对于某个IP地址限制的过程中PIX520的正常工作不受影响，我们应该按照以下步骤来进行操作
1、在内外端口上停掉访问控制列表
pixfirewall# conf tpixfirewall(config)#access-group acl_inside in interface outsidepixfirewall(config)#access-group acl_inside in interface inside
2、去掉访问列表acl_inside
pixfirewall# conf tpixfirewall(config)# no access-list acl-inside
3、重写access-list
pixfirewall(config)# access-list acl_inside deny udp any any eq tftppixfirewall(config)# access-list acl_inside deny tcp any any eq 135pixfirewall(config)# access-list acl_inside deny udp any any eq 135pixfirewall(config)# access-list acl_inside deny tcp any any eq 137pixfirewall(config)# access-list acl_inside deny udp any any eq netbios -nspixfirewall(config)# access-list acl_inside deny tcp any any eq 138pixfirewall(config)# access-list acl_inside deny udp any any eq netbios -dgmpixfirewall(config)# access-list acl_inside deny tcp any any eq netbios -ssnpixfirewall(config)# access-list acl_inside deny udp any any eq 139pixfirewall(config)# access-list acl_inside deny tcp any any eq 445pixfirewall(config)# access-list acl_inside deny tcp any any eq 593pixfirewall(config)# access-list acl_inside deny tcp any any eq 4444pixfirewall(config)# access-list acl_inside permit tcp any any eq 1723pixfirewall(config)# access-list acl_inside permit gre any anypixfirewall(config)# access-list acl_inside deny ip any host 58.61.155.44pixfirewall(config)# access-list acl_inside permit ip any any
即保证permit ip any any这条命令是在最后面一行
4、在内外端口上应用访问列表
pixfirewall(config)#access-gropu acl_inside in inter outsidepixfirewall(config)#access-gropu acl_inside in inter outside
四、验证是否真正的对某个IP地址进行了限制
1、 进行完配置后肯定要先看一下当前配置：show run
2、可以通过tracert命令来验证，如下所示：
C:\>tracert www.ttsou.cnTracing route to www.ttsou.cn [58.61.155.44]over a maximum of 30 hops:1<1 ms<1 ms<1 ms10.75.0.12***Request timed out.3***Request timed out.4***Request timed out.5***Request timed out.
从中可以看出，对于www.ttsou.cn这个网址从三层交换机往上就不通了，证明在PIX520防火墙上已经成功的阻止了对于该网址的访问。
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