What does stateless mean in the context of network security?

Question

network hardware

What does stateless mean in the context of network security?
For example, "routers perform Layer 2-4 stateless inspection at high speed"
or "Stateless and behavioral engines"
links:
www.cs.berkeley.edu/~dawnsong/papers/siff.pdf
ieeexplore.ieee.org/xpl/login. jsp?tp=&arnumber=130...
https://jncie.files.wordpress.com/2008/09/801003_p...

Answer 1

stateless - without saving the session, i.e. the package is analyzed as such, and within one session (for example, opening the page http://www.microsoft.com) there will be many packages back and forth. Who started the session (the client requested a page or the site went to the client) - stateless devices, as a rule, do not know.
The opposite is stateful, i.e. "data is being transferred in one session" is controlled. NAT devices, as a rule, are all stateful
. But stateful firewalls require memory for each session, plus they are much more complicated and expensive to manufacture.

Answer 2

stateless : will allow any incoming UDP packet from the Internet with source 53/udp (which is actively used when scanning)
statefull : will only allow a packet from the DNS server to which a request was sent from inside your network no earlier than 5 minutes ago
an incoming TCP packet with the ACK flag with a source port from the server range you allowed earlier
statefull : will only let through the response packet from the server with which someone from inside your network is currently conducting a TCP dialogue
(all the above examples are exaggerated)