Imagine someone encrypted a virus in application data where you click the link and it eats your PC! You won't find that in circuit level gateway. Instead it's encapsulated and encrypted(if VPN/IPSec is used in some mode-AH or ESP), so security would not be more. Here as you see in the figure, circuit level gateway can't read application data directly. Since application level gateway firewall scans application data but circuit level gateway doesn't do it directly. That's why application firewall requires more time, more resources so it's also called deep-inspection firewall. i.e to filter http traffic, you need http proxy to filter ftp traffic, you need ftp proxy to filter email traffic, you need smtp,pop,imap proxy and so on!Īpplication level gateway firewall scans whole OSI level from top to bottom. so somehow circuit level gateway is transparent.(and the ones I told above)Īpplication level gateway firewall is application specific. Only one difference that I have found is that application gateway doesn't changes the source IP address of packet but circuit level gateway does. So I have confusion(and what I have learnt)-:Īpplication gateway opens 2 TCP connection inbound and outbound and so does circuit gateway.Īpplication gateway just authenticates with username and password but circuit level gateway does not authenticate(then how does it trust the incoming and outgoing users), it is confusing.(or does it authenticates?) Many books are signaling it doesn't do it.Īpplication gateway doesn't examine the content(like packet filtering) and neither does circuit level gateway afaik. Plus the order in which they teach also would mean that circuit level gateway is better than application level gateway. but I've seen people saying circuit level gateway is more powerful than application level gateway. Whereas circuit level gateway only look up to network layer. The example was cool but it didn't make any sense later on to me.Īpplication level gateway can look up to all layers of OSI model Two different TCP connection are formed, inbound and outbound. Packet(from the internal network point of view). The circuit level gateway CHANGES the source ip address of outgoing
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