Packet mode and host-inbound traffic

Did you know that if you enable packet-mode in traffic interface of an SRX box,
host inbound traffic isn’t allowed anymore? Device can still process transit traffic
but inbound traffic won’t work. For example, apply a filter like below to an interface
and try to SSH to IP 98.1.1.1, you shouldn’t be allowed.

#show interfaces
ge-0/0/2 {
    unit 0 {
        family inet {
            filter {
                input inet-packet-mode;
                output inet-packet-mode;
            }
            address 98.1.1.1/24;
        }
    }
}

# top show firewall
family inet {
    filter inet-packet-mode {
        term 10 {
            then {
                packet-mode;
                accept;
            }
        }
    }
}

If you are wondering why: Documentation says that host-inbound traffic is only allowed
if it is sent to flow daemon for inspection.

PS: You can selectively exclude local IP from packet mode but here I just want to show the behavior change.

About: rtoodtoo

Genco has worked for more than 10 years as a Network/Support Engineer. He is also interested in Python, Linux, Security and SD-WAN, currently lives in the Netherlands and works as a Network Support Engineer at Tesla Inc. // JNCIE-SEC #223 / RHCE / PCNSE


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