Question

I want to draw an architecture diagram for a general ERP application.

In that I have come across a confusing point: where should I place the SSL and Firewall?

I tried to figure out exactly where the SSL and Firewall fit in the OSI Model. I know we can use Firewall in Application Layer, Network Layer, Transportation Layer, etc.

Answer 1

A firewall may work at different layers of the OSI model, going from layer 3 to layer 7 (depending on your firewall). Representing it in a diagram will require to set rules for each layer. I would represent the firewall and include a list of all enforced rules on each layer. Some examples could be:

Layer 3: IP filtering
Layer 4: port filtering (TCP/UDP)
Layer 5: session layer firewall (state of the connection)
Layer 6 and 7: application layer firewalls (more inteliggent, can perform deep packet inspection, close to IDS/IPS)

For the "SSL" I presume you mean an SSL offloader. SSL/TLS takes place at the presentation layer or layer 6 of the OSI model.