使用Cisco IOS防火牆的SMTP和ESMTP連線檢查配置示例

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已更新: 2006 年 3 月 3 日
文件 ID:69309

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關於此翻譯

思科已使用電腦和人工技術翻譯本文件，讓全世界的使用者能夠以自己的語言理解支援內容。請注意，即使是最佳機器翻譯，也不如專業譯者翻譯的內容準確。Cisco Systems, Inc. 對這些翻譯的準確度概不負責，並建議一律查看原始英文文件（提供連結）。

簡介

本檔案將提供在Cisco IOS中使用Cisco IOS®防火牆檢查傳入簡易郵件傳送通訊協定(SMTP)或延伸簡易郵件傳送通訊協定(ESMTP)連線的組態範例。此類檢查類似於Cisco PIX 500系列安全裝置中的MailGuard功能。

必要條件

需求

本文件沒有特定需求。

採用元件

本文中的資訊係根據以下軟體和硬體版本：

  • Cisco IOS軟體版本12.3(4)T或更高版本

  • 思科3640路由器

本文中的資訊是根據特定實驗室環境內的裝置所建立。文中使用到的所有裝置皆從已清除（預設）的組態來啟動。如果您的網路正在作用，請確保您已瞭解任何指令可能造成的影響。

慣例

請參閱思科技術提示慣例以瞭解更多有關文件慣例的資訊。

背景資訊

SMTP檢查會導致檢查SMTP命令是否存在非法命令。帶有非法命令的資料包被修改為「xxxx」模式並轉發到伺服器。此過程導致伺服器傳送否定答覆，這會強制客戶端發出有效的命令。非法的SMTP命令是除以下命令以外的任何命令：

  • 資料
  • HELO
  • 說明
  • 郵件
  • NOOP
  • 退出
  • RCPT
  • RSET
  • SAML
  • 傳送
  • SOML
  • VRFY

ESMTP檢查的工作方式與SMTP檢查相同。帶有非法命令的資料包被修改為「xxxx」模式並轉發到伺服器，從而觸發負回覆。非法的ESMTP命令是除以下命令以外的任何命令：

  • 身份驗證
  • 資料
  • EHLO
  • ETRN
  • HELO
  • 說明
  • 說明
  • 郵件
  • NOOP
  • 退出
  • RCPT
  • RSET
  • SAML
  • 傳送
  • SOML
  • VRFY

ESMTP檢查還通過更深入的命令檢查來檢查這些擴展：

  • 郵件大小宣告(SIZE)

  • 遠端佇列處理宣告(ETRN)

  • 二進位MIME(BINARYMIME)

  • 指令流水線

  • 驗證

  • 傳送狀態通知(DSN)

  • 增強狀態代碼(ENHANCEDSTATUSCODE)

  • 8位MIME傳輸(8BITMIME)

附註：  無法同時配置SMTP和ESMTP檢測。嘗試配置這兩種模式會導致出現錯誤消息。

注意：在Cisco IOS軟體版本12.3(4)T和更新版本中，Cisco IOS防火牆不再建立動態存取清單專案來允許流量。Cisco IOS防火牆現在維護一個會話狀態表，以控制檢查連線的安全。

設定

本節提供用於設定本文件中所述功能的資訊。

註：使用Command Lookup Tool(僅供已註冊客戶使用)可獲取本節中使用的命令的詳細資訊。

網路圖表

本檔案會使用以下網路設定：

smtp-esmtp-cbac-1.gif

組態

本檔案會使用以下設定：

3640路由器 
3640-123#show running-config
Building configuration...

Current configuration : 1432 bytes
!
version 12.3
service config
service timestamps debug datetime msec
service timestamps log datetime msec
service password-encryption
!
hostname 3640-123
!
boot-start-marker
boot-end-marker
!
enable password 7 02050D4808095E731F
!
no aaa new-model
!
resource policy
!
voice-card 3
!
ip subnet-zero
!
!
ip cef
no ip dhcp use vrf connected
!
!

!--- This is the Cisco IOS Firewall configuration.


!--- IN-OUT is the inspection rule for traffic that flows !--- from the inside interface of the router to the outside interface.

ip inspect name IN-OUT tcp
ip inspect name IN-OUT udp
ip inspect name IN-OUT ftp
ip inspect name IN-OUT http
ip inspect name IN-OUT icmp


!--- OUT-IN is the inspection rule for traffic that flows !--- from the outside interface of the router to the inside interface. !--- This rule is where SMTP/ESMTP inspection is specified.

ip inspect name OUT-IN smtp
!
no ip ips deny-action ips-interface
!
no ftp-server write-enable
!
!
!
!
controller T1 3/0
 framing sf
 linecode ami
!
!
!
!
!

!--- The outside interface.

interface Ethernet2/0
 ip address 172.22.1.16 255.255.255.0


!--- Apply the access list to permit SMTP/ESMTP connections !--- to the mail server. This also allows Cisco IOS Firewall !--- to inspect SMTP or ESMTP commands.

 ip access-group 101 in
 ip nat outside


!--- Apply the inspection rule OUT-IN inbound on this interface. This is !--- the rule that defines SMTP/ESMTP inspection.

 ip inspect OUT-IN in
 ip virtual-reassembly
 half-duplex
!
interface Serial2/0
 no ip address
 shutdown
!

!--- The inside interface.

interface Ethernet2/1
 ip address 10.10.10.1 255.255.255.0
 ip nat inside


!--- Apply the inspection rule IN-OUT inbound on this interface.

 ip inspect IN-OUT in
 ip virtual-reassembly
 half-duplex
!
ip http server
no ip http secure-server
ip classless
ip route 0.0.0.0 0.0.0.0 172.22.1.1
!
!

!--- The static translation for the mail server.

ip nat inside source static 10.10.10.2 172.22.1.110
ip nat inside source static 10.10.10.5 172.22.1.111
!

!--- The access list to permit SMTP and ESMTP to the mail server. !--- Cisco IOS Firewall inspects permitted traffic.

access-list 101 permit tcp any host 172.22.1.110 eq smtp
!
!
!
control-plane
!
!
!
voice-port 1/0/0
!
voice-port 1/0/1
!
voice-port 1/1/0
!
voice-port 1/1/1
!
!
!
!
!
!
!
!
line con 0
line aux 0
line vty 0 4
 password 7 121A0C0411045D5679
 login
!
!
end

驗證

使用本節內容，確認您的組態是否正常運作。

輸出直譯器工具(僅供已註冊客戶使用)(OIT)支援某些show命令。使用OIT檢視show命令輸出的分析。

  • show ip inspect all — 驗證Cisco IOS防火牆檢查規則的配置及其應用到介面。

    3640-123#show ip inspect all
Session audit trail is disabled
Session alert is enabled
one-minute (sampling period) thresholds are [400:500] connections
max-incomplete sessions thresholds are [400:500]
max-incomplete tcp connections per host is 50. Block-time 0 minute.
tcp synwait-time is 30 sec -- tcp finwait-time is 5 sec
tcp idle-time is 3600 sec -- udp idle-time is 30 sec
dns-timeout is 5 sec
Inspection Rule Configuration
 Inspection name IN-OUT
    tcp alert is on audit-trail is off timeout 3600
    udp alert is on audit-trail is off timeout 30
    ftp alert is on audit-trail is off timeout 3600
    http alert is on audit-trail is off timeout 3600
    icmp alert is on audit-trail is off timeout 10
 Inspection name OUT-IN
    smtp max-data 20000000 alert is on audit-trail is off timeout 3600

Interface Configuration
 Interface Ethernet2/1
  Inbound inspection rule is IN-OUT
    tcp alert is on audit-trail is off timeout 3600
    udp alert is on audit-trail is off timeout 30
    ftp alert is on audit-trail is off timeout 3600
    http alert is on audit-trail is off timeout 3600
    icmp alert is on audit-trail is off timeout 10
  Outgoing inspection rule is not set
  Inbound access list is not set
  Outgoing access list is not set
 Interface Ethernet2/0
  Inbound inspection rule is OUT-IN
    smtp max-data 20000000 alert is on audit-trail is off timeout 3600
  Outgoing inspection rule is not set
  Inbound access list is 101
  Outgoing access list is not set

  • debug ip inspect smtp — 顯示有關Cisco IOS防火牆SMTP檢查事件的消息。

    附註：使用 debug 指令之前，請先參閱有關 Debug 指令的重要資訊。

    ausnml-3600-02#debug ip inspect smtp
INSPECT SMTP Inspection debugging is on
ausnml-3600-02#
*Oct 18 21:51:35.886: CBAC SMTP: reply_type OTHERS 
*Oct 18 21:51:35.886: CBAC SMTP: OTHER REPLY - Reply len: 64, match_len:64, reply_re_state:18
*Oct 18 21:51:35.886: CBAC SMTP: OTHER REPLY match id:13
*Oct 18 21:51:35.886: CBAC SMTP: OTHER REPLY match id:10
*Oct 18 21:51:35.886: CBAC SMTP: End Of Reply Line - index:0 ,len:64


!--- The client issues a command.

*Oct 18 21:51:40.810: CBAC SMTP: VERB - Cmd len:1, match_len:1, cmd_re_state:9
*Oct 18 21:51:40.994: CBAC SMTP: VERB - Cmd len:2, match_len:1, cmd_re_state:24
*Oct 18 21:51:41.190: CBAC SMTP: VERB - Cmd len:3, match_len:1, cmd_re_state:40
*Oct 18 21:51:41.390: CBAC SMTP: VERB - Cmd len:4, match_len:1, cmd_re_state:56
*Oct 18 21:51:41.390: CBAC SMTP: VERB - match id:5
*Oct 18 21:51:42.046: CBAC SMTP: CMD PARAM - Cmd len:5, match_len:1, cmd_re_state:7
*Oct 18 21:51:43.462: CBAC SMTP: CMD PARAM - Cmd len:6, match_len:1, cmd_re_state:2
*Oct 18 21:51:43.594: CBAC SMTP: CMD PARAM - Cmd len:7, match_len:1, cmd_re_state:2
*Oct 18 21:51:43.794: CBAC SMTP: CMD PARAM - Cmd len:9, match_len:2, cmd_re_state:2
*Oct 18 21:51:43.994: CBAC SMTP: CMD PARAM - Cmd len:10, match_len:1, cmd_re_state:2
*Oct 18 21:51:44.194: CBAC SMTP: CMD PARAM - Cmd len:12, match_len:2, cmd_re_state:3
*Oct 18 21:51:44.194: CBAC SMTP: CMD PARAM - match id:6
*Oct 18 21:51:44.194: CBAC SMTP: End Of Command Line - index:1, len:12


!--- The server replies.

*Oct 18 21:51:44.198: CBAC SMTP: reply_type OTHERS 
*Oct 18 21:51:44.198: CBAC SMTP: OTHER REPLY - Reply len: 11, match_len:11, reply_re_state:18
*Oct 18 21:51:44.198: CBAC SMTP: OTHER REPLY match id:13
*Oct 18 21:51:44.198: CBAC SMTP: OTHER REPLY match id:10
*Oct 18 21:51:44.198: CBAC SMTP: End Of Reply Line - index:1 ,len:11


!--- The client issues a command.

*Oct 18 21:51:49.482: CBAC SMTP: VERB - Cmd len:1, match_len:1, cmd_re_state:3
*Oct 18 21:51:50.222: CBAC SMTP: VERB - Cmd len:2, match_len:1, cmd_re_state:15
*Oct 18 21:51:50.618: CBAC SMTP: VERB - Cmd len:3, match_len:1, cmd_re_state:31
*Oct 18 21:51:50.954: CBAC SMTP: VERB - Cmd len:4, match_len:1, cmd_re_state:46
*Oct 18 21:51:50.954: CBAC SMTP: VERB - match id:15
*Oct 18 21:51:51.642: CBAC SMTP: CMD PARAM - Cmd len:5, match_len:1, cmd_re_state:7
*Oct 18 21:51:51.914: CBAC SMTP: CMD PARAM - Cmd len:6, match_len:1, cmd_re_state:2
*Oct 18 21:51:52.106: CBAC SMTP: CMD PARAM - Cmd len:7, match_len:1, cmd_re_state:2
*Oct 18 21:51:54.754: CBAC SMTP: CMD PARAM - Cmd len:8, match_len:1, cmd_re_state:4
*Oct 18 21:51:55.098: CBAC SMTP: CMD PARAM - Cmd len:9, match_len:1, cmd_re_state:2
*Oct 18 21:51:55.322: CBAC SMTP: CMD PARAM - Cmd len:11, match_len:2, cmd_re_state:3
*Oct 18 21:51:55.322: CBAC SMTP: CMD PARAM - match id:6
*Oct 18 21:51:55.322: CBAC SMTP: End Of Command Line - index:2, len:11


!--- The server replies.

*Oct 18 21:51:55.326: CBAC SMTP: reply_type OTHERS 
*Oct 18 21:51:55.326: CBAC SMTP: OTHER REPLY - Reply len: 19, match_len:19, reply_re_state:3
*Oct 18 21:51:55.326: CBAC SMTP: OTHER REPLY match id:13
*Oct 18 21:51:55.326: CBAC SMTP: End Of Reply Line - index:2 ,len:19

*Oct 18 21:51:57.070: CBAC SMTP: VERB - Cmd len:1, match_len:1, cmd_re_state:3
*Oct 18 21:51:57.402: CBAC SMTP: VERB - Cmd len:2, match_len:1, cmd_re_state:15
*Oct 18 21:51:58.162: CBAC SMTP: VERB - Cmd len:3, match_len:1, cmd_re_state:31
*Oct 18 21:51:58.462: CBAC SMTP: VERB - Cmd len:4, match_len:1, cmd_re_state:46
*Oct 18 21:51:58.466: CBAC SMTP: VERB - match id:15
*Oct 18 21:51:58.746: CBAC SMTP: CMD PARAM - Cmd len:5, match_len:1, cmd_re_state:7
*Oct 18 21:51:59.006: CBAC SMTP: CMD PARAM - Cmd len:6, match_len:1, cmd_re_state:2
*Oct 18 21:51:59.234: CBAC SMTP: CMD PARAM - Cmd len:7, match_len:1, cmd_re_state:2
*Oct 18 21:51:59.418: CBAC SMTP: CMD PARAM - Cmd len:9, match_len:2, cmd_re_state:2
*Oct 18 21:51:59.618: CBAC SMTP: CMD PARAM - Cmd len:10, match_len:1, cmd_re_state:2
*Oct 18 21:51:59.818: CBAC SMTP: CMD PARAM - Cmd len:12, match_len:2, cmd_re_state:3
*Oct 18 21:51:59.818: CBAC SMTP: CMD PARAM - match id:6
*Oct 18 21:51:59.818: CBAC SMTP: End Of Command Line - index:3, len:12

*Oct 18 21:51:59.818: CBAC SMTP: reply_type OTHERS 
*Oct 18 21:51:59.818: CBAC SMTP: OTHER REPLY - Reply len: 19, match_len:19, reply_re_state:3
*Oct 18 21:51:59.822: CBAC SMTP: OTHER REPLY match id:13
*Oct 18 21:51:59.822: CBAC SMTP: End Of Reply Line - index:3 ,len:19

*Oct 18 21:52:04.974: CBAC SMTP: VERB - Cmd len:1, match_len:1, cmd_re_state:9
*Oct 18 21:52:05.170: CBAC SMTP: VERB - Cmd len:2, match_len:1, cmd_re_state:24
*Oct 18 21:52:05.326: CBAC SMTP: VERB - Cmd len:3, match_len:1, cmd_re_state:40
*Oct 18 21:52:05.526: CBAC SMTP: VERB - Cmd len:4, match_len:1, cmd_re_state:55
*Oct 18 21:52:05.526: CBAC SMTP: VERB - match id:6
*Oct 18 21:52:05.742: CBAC SMTP: CMD PARAM - Cmd len:6, match_len:2, cmd_re_state:3
*Oct 18 21:52:05.742: CBAC SMTP: CMD PARAM - match id:6
*Oct 18 21:52:05.742: CBAC SMTP: End Of Command Line - index:4, len:6

*Oct 18 21:52:05.746: CBAC SMTP: reply_type OTHERS 
*Oct 18 21:52:05.746: CBAC SMTP: OTHER REPLY - Reply len: 54, match_len:54, reply_re_state:3
*Oct 18 21:52:05.746: CBAC SMTP: OTHER REPLY match id:13
*Oct 18 21:52:05.746: CBAC SMTP: End Of Reply Line - index:4 ,len:54

*Oct 18 21:52:05.746: CBAC SMTP: reply_type OTHERS 
*Oct 18 21:52:05.746: CBAC SMTP: OTHER REPLY - Reply len: 15, match_len:15, reply_re_state:3
*Oct 18 21:52:05.746: CBAC SMTP: OTHER REPLY match id:13
*Oct 18 21:52:05.746: CBAC SMTP: End Of Reply Line - index:5 ,len:15

*Oct 18 21:52:05.746: CBAC SMTP: reply_type OTHERS 
*Oct 18 21:52:05.746: CBAC SMTP: OTHER REPLY - Reply len: 15, match_len:15, reply_re_state:3
*Oct 18 21:52:05.746: CBAC SMTP: OTHER REPLY match id:13
*Oct 18 21:52:05.746: CBAC SMTP: End Of Reply Line - index:6 ,len:15

*Oct 18 21:52:05.746: CBAC SMTP: reply_type OTHERS 
*Oct 18 21:52:05.750: CBAC SMTP: OTHER REPLY - Reply len: 6, match_len:6, reply_re_state:3
*Oct 18 21:52:05.750: CBAC SMTP: OTHER REPLY match id:13
*Oct 18 21:52:05.750: CBAC SMTP: End Of Reply Line - index:7 ,len:6

*Oct 18 21:52:05.750: CBAC SMTP: reply_type OTHERS 
*Oct 18 21:52:05.750: CBAC SMTP: OTHER REPLY - Reply len: 19, match_len:19, reply_re_state:3
*Oct 18 21:52:05.750: CBAC SMTP: OTHER REPLY match id:13
*Oct 18 21:52:05.750: CBAC SMTP: End Of Reply Line - index:8 ,len:19

*Oct 18 21:52:05.750: CBAC SMTP: reply_type OTHERS 
*Oct 18 21:52:05.750: CBAC SMTP: OTHER REPLY - Reply len: 17, match_len:17, reply_re_state:3
*Oct 18 21:52:05.750: CBAC SMTP: OTHER REPLY match id:13
*Oct 18 21:52:05.750: CBAC SMTP: End Of Reply Line - index:9 ,len:17

*Oct 18 21:52:05.750: CBAC SMTP: reply_type OTHERS 
*Oct 18 21:52:05.750: CBAC SMTP: OTHER REPLY - Reply len: 6, match_len:6, reply_re_state:3
*Oct 18 21:52:05.750: CBAC SMTP: OTHER REPLY match id:13
*Oct 18 21:52:05.754: CBAC SMTP: End Of Reply Line - index:10 ,len:6

*Oct 18 21:52:05.754: CBAC SMTP: reply_type OTHERS 
*Oct 18 21:52:05.754: CBAC SMTP: OTHER REPLY - Reply len: 6, match_len:6, reply_re_state:3
*Oct 18 21:52:05.754: CBAC SMTP: OTHER REPLY match id:13
*Oct 18 21:52:05.754: CBAC SMTP: End Of Reply Line - index:11 ,len:6

*Oct 18 21:52:05.754: CBAC SMTP: reply_type OTHERS 
*Oct 18 21:52:05.754: CBAC SMTP: OTHER REPLY - Reply len: 6, match_len:6, reply_re_state:3
*Oct 18 21:52:05.754: CBAC SMTP: OTHER REPLY match id:13
*Oct 18 21:52:05.754: CBAC SMTP: End Of Reply Line - index:12 ,len:6

*Oct 18 21:52:05.754: CBAC SMTP: reply_type OTHERS 
*Oct 18 21:52:05.754: CBAC SMTP: OTHER REPLY - Reply len: 3, match_len:3, reply_re_state:3
*Oct 18 21:52:05.754: CBAC SMTP: OTHER REPLY match id:13
*Oct 18 21:52:05.754: CBAC SMTP: End Of Reply Line - index:13 ,len:3

*Oct 18 21:52:15.646: CBAC SMTP: VERB - Cmd len:1, match_len:1, cmd_re_state:6
*Oct 18 21:52:15.838: CBAC SMTP: VERB - Cmd len:3, match_len:2, cmd_re_state:37
*Oct 18 21:52:16.206: CBAC SMTP: VERB - Cmd len:4, match_len:1, cmd_re_state:52
*Oct 18 21:52:16.206: CBAC SMTP: VERB - match id:9
*Oct 18 21:52:18.954: CBAC SMTP: CMD PARAM - Cmd len:6, match_len:2, cmd_re_state:3
*Oct 18 21:52:18.958: CBAC SMTP: CMD PARAM - match id:6
*Oct 18 21:52:18.958: CBAC SMTP: End Of Command Line - index:5, len:6

*Oct 18 21:52:18.958: CBAC SMTP: reply_type OTHERS 
*Oct 18 21:52:18.958: CBAC SMTP: OTHER REPLY - Reply len: 21, match_len:21, reply_re_state:18
*Oct 18 21:52:18.958: CBAC SMTP: OTHER REPLY match id:13
*Oct 18 21:52:18.958: CBAC SMTP: OTHER REPLY match id:10
*Oct 18 21:52:18.958: CBAC SMTP: End Of Reply Line - index:14 ,len:21

疑難排解

目前尚無適用於此組態的具體疑難排解資訊。

相關資訊

修訂記錄

修訂 發佈日期 意見
1.0
03-Mar-2006
初始版本

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