Routing Table Checking Flow - ZyXEL Communications ZYWALL USG 20 Manual

Chapter 6 Configuration Basics
Traffic in > Defragmentation > Destination NAT > Routing > Stateful Firewall >
ADP > Application Classification > Content Filter > Anti-Spam > SNAT >
Bandwidth Management > Fragmentation > Traffic Out.
Figure 51 Packet Flow
The packet flow is as follows:
• Automatic SNAT and WAN trunk routing for traffic going from internal to
external interfaces (you don't need to configure anything to all LAN to WAN
traffic).
The ZyWALL automatically adds all of the external interfaces to the default WAN
trunk. External interfaces include ppp and cellular interfaces as well as any
Ethernet interfaces that are set as external interfaces.
Examples of internal interfaces are any Ethernet interfaces that you configure as
internal interfaces.
• A policy route can be automatically disabled if the next-hop is dead.
• You do not need to set up policy routes for IPSec traffic.
• Policy routes can override direct routes.
• You do not need to set up policy routes for 1:1 NAT entries.
• You can create Many 1:1 NAT entries to translate a range of private network
addresses to a range of public IP addresses
• Static and dynamic routes have their own category.

6.4.1 Routing Table Checking Flow

When the ZyWALL receives packets it defragments them and applies destination
NAT. Then it examines the packets and determines how to route them. The
checking flow is from top to bottom. As soon as the packets match an entry in one
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ZyWALL USG 20/20W User's Guide