Dell NSA E5500 Getting Started Manual page 45

Note: Do not enable Never route traffic on the bridge-pair
unless your network topology requires that all packets
entering the L2 Bridge remain on the L2 Bridge
segments.
You may optionally enable the Block all non-IPv4
traffic setting to prevent the L2 bridge from passing
non-IPv4 traffic.
If You Are Following
Scenario...
C - L2 Bridge Mode
45 | Configuring L2 Bridge Mode
Proceed to Section:
Additional Deployment Configuration
- page 46