Disable TCP session inspection NS5GT

  • Hi,

    I have a scenario where a NS5GT (ScreenOS 5.4.0r8.0) will have to pass packets belonging to a TCP session, which has already been established via a different route (i.e. disable stateful inspection and just pass packets). Background: Terminal RDP Session should continue, after a backup route has become active. The session will already have been established via the primary route, but packets will need to be forwarded through a netscreen on the backup route.

    I have disabled screening between the relevant zones, and TCP SYN checking on the device (see “get flow” output below). Is there anything else that needs to be done/configured for it to work?

    ns5gt-> get flow
    flow action flag: 1075
    flow GRE outbound tcp-mss is not set
    flow GRE inbound tcp-mss is not set
    flow change tcp mss option for all packets is not set
    flow change tcp mss option for vpn packets = 1392
    flow deny session disabled
    TCP syn-proxy syn-cookie disabled
    Allow dns reply pkt without matched request : NO
    Check TCP SYN bit before create session : NO
    Check TCP SYN bit before create session for tunneled packets : NO
    Use Hub-and-Spoke policies for Untrust MIP traffic that loops on same interface
    Check  unknown mac flooding : YES
    Skip sequence number check in stateful inspection : YES
    ICMP path mtu discovery : NO
    ICMP time exceeded : NO
    TCP RST invalidates session immediately : NO
    flow log info:>,0
    flow initial session timeout: 20 seconds
    flow session cleanup time: 2 seconds
    early ageout setting:
            high watermark = 100 (2064 sessions)
            low watermark  = 100 (2064 sessions)
            early ageout  = 2
            RST seq. chk OFF
    MAC cache for management traffic: OFF
    Fix tunnel outgoing interface: OFF
    session timeout on route change is not set

    Would be grateful for any advice!

  • Try below command.

    unset flow tcp-syn-check

  • Engineer

    Unfortunately, there is no option to disable stateful inspection on ScreenOS.