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Updated:November 18, 2020
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This document describes how to use the Cisco Adaptive Security Appliance (ASA) with the Context Aware (CX) module, also known as the Next Generation firewall, and Cisco Cloud Web Security (CWS) Connector.
Cisco recommends that you have:
3DES/AES License on ASA (Free license)
Valid CWS service/license to use CWS for the required number of users
Access to ScanCenter Portal to generate the Authentication Key
This document is not restricted to specific software and hardware versions.
The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, make sure that you understand the potential impact of any command.
This document shows these areas of technology and products:
Cisco ASA 5500-X Series Adaptive Security Appliances provides Internet edge firewall security and intrusion prevention.
Cisco Cloud Web Security provides granular control over all web content that is accessed.
The ASA CX/FirePower module has the capability to support both the Content Security and Intrusion Prevention requirement, dependent upon the license features enabled on the ASA CX/FirePower. Cloud Web Security is not supported with the ASA CX/FirePower module. If you configure both the ASA CX/FirePower action and Cloud Web Security inspection for the same traffic flow, the ASA only performs the ASA CX/FirePower action. In order to leverage the CWS features for Web Security, you need to ensure the traffic is bypassed in the match statement for ASA CX/FirePower. Typically, in such a scenario, customers will use CWS for Web Security and AVC (port 80 and 443) and CX/FirePower module for all other ports.
The match default-inspection-traffic command does not include the default ports for the Cloud Web Security inspection (80 and 443).
Actions are applied to traffic bidirectionally or unidirectionally dependent upon the feature. For features that are applied bidirectionally, all traffic that enters or exits the interface to which you apply the policy map is affected if the traffic matches the class map for both directions. When you use a global policy all features are unidirectional; features that are normally bidirectional when applied to a single interface only apply to the ingress of each interface when applied globally. Because the policy is applied to all interfaces, the policy is applied in both directions so bidirectionality in this case is redundant.
For TCP and UDP traffic (and Internet Control Message Protocol (ICMP) when you enable stateful ICMP inspection), service policies operate on traffic flows and not just individual packets. If traffic is part of an existing connection that matches a feature in a policy on one interface, that traffic flow cannot also match the same feature in a policy on another interface; only the first policy is used.
Interface service policies take precedence over the global service policy for a given feature.
The maximum number of policy maps is 64, but you can only apply one policy map per interface.
Traffic Flow for the ASA and CWS
The user requests the URL via the web browser.
Traffic is sent to the ASA to go out the Internet. The ASA performs required NAT and based on the protocol HTTP/HTTPS, matches to the inside interface policy and gets redirected to Cisco CWS.
CWS analyzes the request based on the configuration done in the ScanCenter portal and if policy permits, forwards the request to approved sites.
CWS inspects the returned traffic and redirects the same to ASA.
Based on the session flow maintained, ASA sends traffic back to the user.
Traffic Flow for the ASA and CX/FirePower
All traffic other than HTTP and HTTPS is configured to match the ASA CX/FirePower for inspection and is redirected to CX/FirePower over the ASA backplane.
The ASA CX/FirePower inspects traffic based on the policies configured and takes the required allow/block/alert action.
Access List to Match All Internet Bound Web (TCP/80) Traffic and Exclude All Internal Traffic
!ASA CWS HTTP Match access-list cws-www extended deny ip any4 10.0.0.0 255.0.0.0 access-list cws-www extended deny ip any4 172.16.0.0 255.240.0.0 access-list cws-www extended deny ip any4 192.168.0.0 255.255.0.0 access-list cws-www extended permit tcp any4 any4 eq www
Access List to Match All Internet Bound HTTPS (TCP/443) Traffic and Exclude All Internal Traffic
!ASA CWS HTTPS Match access-list cws-https extended deny ip any4 10.0.0.0 255.0.0.0 access-list cws-https extended deny ip any4 172.16.0.0 255.240.0.0 access-list cws-https extended deny ip any4 192.168.0.0 255.255.0.0 access-list cws-https extended permit tcp any4 any4 eq https
Access List to Match All Internal Traffic, Exclude All Internet Bound Web and HTTPS Traffic and All Other Ports
Class Map Configuration to Match Traffic for Both CWS and CX/FirePower
! Match HTTPS traffic for CWS class-map cmap-https match access-list cws-https
! Match HTTP traffic for CWS class-map cmap-http match access-list cws-www
! Match traffic for ASA CX/FirePower class-map cmap-ngfw match access-list asa-ngfw
Policy Map Configuration to Associate Actions with Class Maps
!Inspection policy map to configure essential parameters for the rules and optionally !identify the allowed list for HTTP traffic policy-map type inspect scansafe http-pmap parameters default group cws_default http
!Inspection policy map to configure essential parameters for the rules and optionally !identify the allowed list for HTTPS traffic policy-map type inspect scansafe https-pmap parameters default group cws_default https
! Interface policy local to Inside Interface policy-map cws_policy class cmap-http inspect scansafe http-pmap fail-open class cmap-https inspect scansafe https-pmap fail-open
! Global Policy with Inspection enabled using ASA CX policy-map global_policy class inspection_default <SNIP> class cmap-ngfw cxsc fail-open class class-default user-statistics accounting
Activate Policy Globally for CX/FirePower and CWS on the Interface
service-policy global_policy global service-policy cws_policy inside
Note: In this example, it is assumed that web traffic originates only from inside the security zone. You can use interface policies on all interfaces where you expect web traffic or use the same classes within the global policy. This is just to demonstrate the functioning of CWS and use of MPF in order to support our requirement.
Enable CWS on the ASA (No Difference)
scansafe general-options server primary ip 203.0.113.1 port 8080 server backup ip 203.0.113.2 port 8080 retry-count 5 license xxxxxxxxxxxxxxxxxxxxxxxxxxx !
In order to ensure that all connections use the new policy, you need to disconnect the current connections so they can reconnect with the new policy. See the clear conn or clear local-host commands.
Use this section to confirm that your configuration works properly.
Enter the show scansafe statistics command in order to verify the service to be enabled and that the ASA redirects traffic. Subsequent tries show the increment in session counts, current sessions, and bytes transferred.
csaxena-cws-asa# show scansafe statistics Current HTTP sessions : 0 Current HTTPS sessions : 0 Total HTTP Sessions : 1091 Total HTTPS Sessions : 5893 Total Fail HTTP sessions : 0 Total Fail HTTPS sessions : 0 Total Bytes In : 473598 Bytes Total Bytes Out : 1995470 Bytes HTTP session Connect Latency in ms(min/max/avg) : 10/23/11 HTTPS session Connect Latency in ms(min/max/avg) : 10/190/11
Enter the show service-policy command in order to see the increments in packets inspected
asa# show service-policy Global policy: Service-policy: global_policy Class-map: inspection_default <SNIP> <SNIP> Class-map: cmap-ngfw CXSC: card status Up, mode fail-open, auth-proxy disabled packet input 275786624, packet output 272207060, drop 0,reset-drop 36,proxied 0 Class-map: class-default Default Queueing Packet recieved 150146, sent 156937, attack 2031
This section provides information you can use to troubleshoot your configuration.
In order to troubleshoot any issues related to the above configuration and to understand the packet flow, enter this command:
asa(config)# packet-tracer input inside tcp 10.0.0.1 80 192.0.2.105 80 det
Phase: 1 Type: CAPTURE Subtype: Result: ALLOW Config: Additional Information: <SNIP> <This phase will show up if you are capturing same traffic as well>
Phase: 2 Type: ACCESS-LIST Subtype: Result: ALLOW Config: Implicit Rule Additional Information: Forward Flow based lookup yields rule: in <SNIP>
Phase: 3 Type: ROUTE-LOOKUP Subtype: Resolve Egress Interface Result: ALLOW Config: Additional Information: in 0.0.0.0 0.0.0.0 via 198.51.100.1, outside <Confirms egress interface selected. We need to ensure we have CWS connectivity via the same interface>
Phase: 4 Type: ROUTE-LOOKUP Subtype: Resolve Egress Interface Result: ALLOW Config: Additional Information: in 10.0.0.0 255.255.254.0 via 10.0.0.0.1, inside
Phase: 5 Type: ACCESS-LIST Subtype: log Result: ALLOW Config: access-group inside_in in interface inside access-list inside_in extended permit ip any any Additional Information: <SNIP>
Phase: 6 Type: NAT Subtype: Result: ALLOW Config: object network obj-inside_to_outside nat (inside,outside) dynamic interface Additional Information: Dynamic translate 10.0.0.1/80 to 198.51.100.1/80 Forward Flow based lookup yields rule: in <SNIP>
Phase: 7 Type: NAT Subtype: per-session Result: ALLOW Config: Additional Information: Forward Flow based lookup yields rule: in <SNIP>
Phase: 8 Type: IP-OPTIONS Subtype: Result: ALLOW Config: Additional Information: Forward Flow based lookup yields rule: in <SNIP>
Phase: 10 Type: CXSC Subtype: Result: ALLOW Config: class-map ngfw-cx match access-list asa-cx policy-map global_policy class ngfw cxsc fail-open service-policy global_policy global Additional Information: Forward Flow based lookup yields rule: in id=0x7fff2c530970, priority=71, domain=cxsc, deny=true hits=5868,user_data=0x7fff2c931380,cs_id=0x0,use_real_addr,flags=0x0,protocol=6 src ip/id=0.0.0.0, mask=0.0.0.0, port=0, tag=0 dst ip/id=0.0.0.0, mask=0.0.0.0, port=80, tag=0, dscp=0x0 input_ifc=inside, output_ifc=any
Phase: 11 Type: Subtype: Result: ALLOW Config: Additional Information: Forward Flow based lookup yields rule: out <SNIP>
Phase: 12 Type: Subtype: Result: ALLOW Config: Additional Information: Forward Flow based lookup yields rule: out <SNIP>
Phase: 13 Type: USER-STATISTICS Subtype: user-statistics Result: ALLOW Config: Additional Information: Forward Flow based lookup yields rule: out <SNIP> <In this example, IDFW is not configured>
Phase: 14 Type: NAT Subtype: per-session Result: ALLOW Config: Additional Information: Reverse Flow based lookup yields rule: in <SNIP>
Phase: 15 Type: IP-OPTIONS Subtype: Result: ALLOW Config: Additional Information: Reverse Flow based lookup yields rule: in <SNIP>
Phase: 16 Type: USER-STATISTICS Subtype: user-statistics Result: ALLOW Config: Additional Information: Reverse Flow based lookup yields rule: out <SNIP>
Phase: 17 Type: FLOW-CREATION Subtype: Result: ALLOW Config: Additional Information: New flow created with id 3855350, packet dispatched to next module Module information for forward flow ... snp_fp_tracer_drop snp_fp_inspect_ip_options snp_fp_tcp_normalizer snp_fp_inline_tcp_mod snp_fp_translate snp_fp_tcp_normalizer snp_fp_adjacency snp_fp_fragment snp_ifc_stat
Module information for reverse flow ... snp_fp_tracer_drop snp_fp_inspect_ip_options snp_fp_tcp_normalizer snp_fp_translate snp_fp_inline_tcp_mod snp_fp_tcp_normalizer snp_fp_adjacency snp_fp_fragment snp_ifc_stat
Result: input-interface: inside input-status: up input-line-status: up output-interface: outside output-status: up output-line-status: up Action: allow