Network Router User Manual

Chapter 20: Security Configuration Guide
286 SmartSwitch Router User Reference Manual
Layer-4 Bridging and Filtering
Layer-4 bridging is the SSR’s ability to use layer-3/4 information to perform filtering or
QoS during bridging. As described in “Layer-2 Security Filters” above, you can configure
ports to filter traffic using MAC addresses. Layer-4 bridging adds the ability to use IP
addresses, layer-4 protocol type, and port number to filter traffic in a bridged network.
Layer-4 bridging allows you to apply security filters on a “flat” network, where the client
and server may reside on the same subnet.
Note:
Ports that are included in a layer-4 bridging VLAN must reside on updated SSR
hardware. Please refer to Appendix A for details.
To illustrate this, the following diagram shows an SSR serving as a bridge for a consultant
host, file server, and an engineering host, all of which reside on a single subnet.
Figure 25. Sample VLAN for Layer-4 bridging
You may want to allow the consultant access to the file server for e-mail (SMTP) traffic,
but not for Web (HTTP) traffic and allow e-mail, Web, and FTP traffic between the
engineer and the file server. You can use Layer-4 bridging to set this up.
Setting up Layer-4 bridging consists of the following steps:
• Creating a port-based VLAN
• Placing the ports on the same VLAN
• Enabling Layer-4 Bridging on the VLAN
• Creating an ACL that specifies the selection criteria
• Applying an ACL to a port
et.1.1 et.1.2
Consultant File Server
SSR
1.1.1.1/24
1.1.1.2/24
Engineer
et.1.3
1.1.1.3/24