Cisco ASA Firewall Archives

VPN client Error -Syslog ID 305006


Network topology. Remote brach office with ASA firewall and VPN client on the remote LAN. Central Site with ASA firewall terminating the remote branch VPN client. I can not connect from inside my branch network to central network using VPN client. Earlier i had in my office FreeBSD and did not have this problem (I could connect to Central ASA using VPN client), when i changed FreeBSD to ASA this problem occur. VPN client is connected, tunnel is created but nothing more.
I get an error message :Syslog ID 305006 – regular translation creation failed for protocol 50 src inside: dst outside:6.168.y.x


On remote branch office ASA use:

ciscoasa(config)# policy-map global_policy
ciscoasa(config-pmap)# class inspection_default
ciscoasa(config-pmap-c)# inspect ipsec-pass-thru

On Central Office ASA use:

PIX/ASA 7.1 and earlier: pix(config)#isakmp nat-traversal 20

PIX/ASA 7.2(1) and later: securityappliance(config)#crypto isakmp nat-traversal 20

Cisco ASA ftp inspection purpose

By default, the global policy used on a Cisco ASA firewall enables FTP inspection for all traffic passing through the appliance. Before discussing the usage of ftp inspection, let’s see how ftp works:

In Active FTP (which is the default mode), we need two ports for communication. Port 21 is used for Command and Control traffic and Port 20 is used for Data transfer. The FTP client connects from a random source port bigger than 1023 (N>1023) to the command port of the FTP server (port 21). Then the client starts listening to port N+1 and notifies the server that it will accept data to this port (N+1). The server then connects back to the specified data port of the client from its local data source port 20.


Now, the above behavior works fine if there is no firewall between the FTP client and server. However, if there is a stateful firewall between the two ftp nodes, we have a problem. Specifically, when the FTP server will start its Data connection back to the client (in order to start sending traffic), the firewall will block this data communication because it will start from a different source port (20 instead of 21). The purpose therefore of the inspect ftp command on the Cisco ASA is to listen for the initial Command FTP traffic (on port 21) and dynamically open a secondary Data connection between FTP server and client (from port 20). This will allow FTP communication to work. If you disable FTP inspection with the no inspect ftp command, outbound users can start connections only in passive mode, and all inbound FTP is disabled.

The inspect ftp command is found under the global policy map:

policy-map global_policy
class inspection_default
inspect ftp

ASA 5505,5510 Base Vs Security Plus License

Cisco ASA 5505 Image Cisco ASA 5510 Image

The two smallest ASA Firewall models, the 5505 and the 5510, are the only ones that have two types of licenses. They can be ordered either with a Base License or a Security Plus License. Many customers of mine are always asking me what the difference is between the two licenses (except from the price of course), so I thought it would be useful to summarize below the differences between the two license types:

Cisco ASA 5505

Base License

Security Plus License

10,000 Maximum Firewall Connections 25,000 Maximum Firewall Connections
10 Maximum VPN Sessions (site-to-site and remote access) 25 Maximum VPN Sessions (site-to-site and remote access)
3 Maximum VLANs (Trunking Disabled)(2 regular zones and 1 restricted zone that can only communicate with 1 other zone) 20 Maximum VLANs (Trunking enabled)(No restrictions of traffic flow between zones)
No High Availability (failover) supported Supports Stateless Active/Standby failover

Cisco ASA 5510

Base License

Security Plus License

50,000 Maximum Firewall Connections 130,000 Maximum Firewall Connections
5×10/100Integrated Network Interfaces 2×10/100/1000 and3×10/100

Integrated Network Interfaces

50 Maximum VLANs 100 Maximum VLANs
No High Availability (failover) supported Supports Active/Active andActive/Standby failover
No Security Contexts (Virtual Firewalls) Supports 2 Virtual Firewalls (included) and 5 maximum.
No Support for VPN Clustering and VPN Load Balancing Supports VPN Clustering and VPN Load Balancing

Which Cisco ASA Models support IPS Module

As we mentioned in previous posts, the Cisco ASA 5500 appliance supports an Intrusion Detection/Intrusion Prevention plug-in module (AIP-SSM). However not all models support this. Specifically only the middle-range models support it. The lowest-end model (5505) and the highest-end models (5550, 5580) does not support the AIP-SSM IPS module.

ASA Models that support IPS Module:

  • Cisco ASA 5510
  • Cisco ASA 5520
  • Cisco ASA 5540

Basically the ASA 5505 can not support the AIP-SSM because of its small size. Also, the 5550 can not support the module because its hardware is occupied with much more integrated network ports compared with other models (it has 8-10/100/1000 and 4 gigabit SFP ports). The highest-end 5580 does not support the module because an IPS inline module in the 5580 would decrease its packet forwarding performance (remember that the 5580 is usually used in high traffic environments).

The CSC-SSM module of the Cisco ASA 5500 Firewall offers content security inspection for FTP, HTTP, POP3, and SMTP traffic, thus protecting the network from viruses, spyware, worms, spam and phishing, and controls unwanted mail and Web content. In more detail, the capabilities of the CSC-SSM module include the following:

  • Antivirus and Antispyware protection using the Trend Micro technology.
  • URL filtering
  • content filtering
  • email filtering
  • anti-phishing protection in Web and email.
  • Anti-spam protection in email.

After initial installation and configuration of the CSC-SSM module, you need to configure the ASA Firewall to send specific traffic to the module for inspection. The traffic supported for inspection is FTP, HTTP, POP3 and SMTP as we mentioned above. For SMTP traffic, the inspection works only for inbound traffic from the Internet towards internal SMTP servers protected by the ASA appliance. The flow of scanned traffic with the CSC-SSM module is shown on the figure below (figure courtesy of

csc ssm traffic flow inspection

To configure the Cisco ASA Firewall to send traffic to the content inspection module we need to use the modular policy framework as following:

Configuring the Cisco ASA to work with CSC-SSM:

Assume we have an internal network range of We want to configure the CSC-SSM module to inspect outbound HTTP, FTP, and POP3 traffic from our internal hosts towards the Internet.

! First define what traffic to inspect
ASA(config)# access-list inspect_outbound extended permit tcp any eq 80
ASA(config)# access-list inspect_outbound extended permit tcp any eq 21
ASA(config)# access-list inspect_outbound extended permit tcp any eq 110

! Create a class map to identify the traffic that should be diverted to the CSC SSM
ASA(config)# class-map csc_outbound_class
ASA(config-cmap)# match access-list inspect_outbound

! Create a policy map and attach the class-map
ASA(config)# policy-map csc_out_policy
ASA(config-pmap)# class csc_outbound_class
ASA(config-pmap-c)# csc fail-open

! Apply the policy map globally or to a specific interface (inside in our case)
ASA(config-pmap-c)# service-policy csc_out_policy interface inside

The csc fail-open command under the policy-map controls how the adaptive security appliance handles traffic when the CSC SSM is unavailable. The fail-open keyword specifies that all traffic will be permitted in case the CSC module fails. The other option is fail-close.

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