Cisco ASA 防火墙巨有效的排错命令

　　大家经常用电脑或者网络设备上的traceroute，跟踪一个包从一个设备到另一个设备中间的路径，其实在PIX上还有一个命令可以跟踪一个数据包从一个接口到另一个接口

　　内部处理时经过的各个步骤，如acl,nat,vpn等

　　Packet-Tracer

　　New Reader Tip: Troubleshooting Access Problems Using Packet-Tracer

　　Troubleshooting access problems through a firewall is often very difficult, especially when speed to resolution is critical. Errors in long complex ACLs can be

　　easily overlooked, and access failures caused by NAT, IDS, and routing make the problem even more difficult.

　　Cisco has released an incredible new feature in ASA software version 7.2(1) that virtually eliminates the guesswork. Packet-tracer allows a firewall administrator to

　　inject a virtual packet into the security appliance and track the flow from ingress to egress. Along the way, the packet is evaluated against flow and route lookups,

　　ACLs, protocol inspection, NAT, and IDS. The power of the utility comes from the ability to simulate real-world traffic by specifying source and destination addresses

　　with protocol and port information.

　　Packet-tracer is available both from the CLI and in the ASDM. The ASDM version even includes animation (the value of which is questionable, but it is fun to watch),

　　and the ability to navigate quickly to a failed policy.

　　Here is the CLI syntax:

　　packet-tracer input [src_int] protocol src_addr src_port dest_addr dest_port [detailed] [xml]

　　A few examples of truncated output show some of the most useful features. Not only does the tool show the result of an ACL evaluation, but also the specific

　　ACE that either permits or denies the packet, including a hit on the implicit deny.

　　asaTestlab# "packet-tracer input inside tcp 10.1.1.1 1024 10.4.1.1 23"

　　Phase: 3

　　Type: ACCESS-LIST

　　Subtype: log

　　Result: ALLOW

　　Config:

　　access-group inside in interface inside access-list inside extended permit ip any 10.4.1.0 255.255.255.0

　　Additional Information:

　　asaTestlab# "packet-tracer input inside tcp 10.1.1.1 1024 10.4.2.1 5282"

　　Phase: 3

　　Type: ACCESS-LIST

　　Subtype: log

　　Result: DROP

　　Config:

　　access-group inside in interface inside access-list inside extended deny tcp any host 10.4.2.1 eq 5282

　　Additional Information:

　　Evaluations of other elements of the config are similarly specific. Here is an example with nat-control enabled but without proper address translation defined:

　　asaTestlab# "packet-tracer input DMZ tcp 10.2.1.1 1024 10.4.2.1 http"

　　Phase: 7

　　Type: NAT

　　Subtype:

　　Result: DROP

　　Config:

　　nat (DMZ) 0 access-list NoNAT

　　nat-control

　　match ip DMZ any outside any

　　no translation group, implicit deny

　　policy_hits = 1

　　--------------------------------------------

　　实例，在PIX515E，OS7.2上配置remote access vpn，配置好了用vpn client连接，正常，但怎么也ping不通防火墙内网的IP地址，

　　这时看cliet statistics的discard的包很多，sent bytes很多，received byte为0，decrypted 为0，可以判断是包过去了，但回不来，

　　但出在哪个地方呢，看配置文件一条一条看很烦的，也不容易查找问题，这时用packet-tracer 模拟一个包从外口进来到内口的数据包处理过程，

　　Pix1(config)# packet-tracer input outside tcp 172.16.70.200 1024 172.16.10 23

　　-----------------------模拟outside接口的地址172.16.70.200 telnet到inside接口的172.16.10

　　-----------------------数据包从outside口进来

　　Phase: 1

　　Type: FLOW-LOOKUP

　　Subtype:

　　Result: ALLOW

　　Config:

　　Additional Information:

　　Found no matching flow, creating a new flow

　　-----------------------查找路由，OK

　　Phase: 2

　　Type: ROUTE-LOOKUP

　　Subtype: input

　　Result: ALLOW

　　Config:

　　Additional Information:

　　in 172.16.100.0 255.255.255.0 inside

　　-----------------------检查outside的ACL，OK

　　Phase: 3

　　Type: ACCESS-LIST

　　Subtype: log

　　Result: ALLOW

　　Config:

　　access-group 102 in interface outside

　　access-list 102 extended permit ip any any

　　Additional Information:

　　Phase: 4

　　Type: IP-OPTIONS

　　Subtype:

　　Result: ALLOW

　　Config:

　　Additional Information:

　　Phase: 5

　　Type: CP-PUNT

　　Subtype:

　　Result: ALLOW

　　Config:

　　Additional Information:

　　-----------------------应用ipsec 协议加密，OK，这时应该是数据包从inside到outside发送了

　　Phase: 6

　　Type: VPN

　　Subtype: ipsec-tunnel-flow

　　Result: ALLOW

　　Config:

　　Additional Information:

　　-----------------------返回的数据包本应该是ipsec 加密的，这时却被NAT检查，很明显nat 0忘了定义。

　　Phase: 7

　　Type: NAT

　　Subtype: rpf-check

　　Result: DROP

　　Config:

　　nat (inside) 0 access-list vpnl2l_list

　　nat (inside) 1 access-list 101

　　nat-control

　　match ip inside any outside any

　　dynamic translation to pool 1 (58.248.27.57)

　　translate_hits = 75970, untranslate_hits = 87806

　　Additional Information:

　　-----------------------最后的结果是drop

　　Result:

　　input-interface: outside

　　input-status: up

　　input-line-status: up

　　output-interface: inside

　　output-status: up

　　output-line-status: up

　　Action: drop

　　Drop-reason: (acl-drop) Flow is denied by configured rule