Port Traffic Controls

Jumbo Frames

If there are security concerns with grouping the ports as shown for VLAN 300, you can either use source-port filtering to block unwanted traffic paths or create separate jumbo VLANs, one for ports 6 and 7, and another for ports 12 and 13.

■Outbound Jumbo Traffic. Any port operating at 1 Gbps or higher can transmit outbound jumbo frames through any VLAN, regardless of the jumbo configuration. The VLAN is not required to be jumbo-enabled, and the port is not required to belong to any other, jumbo enabled VLANs. This can occur in situations where a non-jumbo VLAN includes some ports that do not belong to another, jumbo-enabled VLAN and some ports that do belong to another, jumbo-enabled VLAN. In this case, ports capable of receiving jumbo frames can forward them to the ports in the VLAN that do not have jumbo capability.

 

1

 

 

2

 

 

 

3

 

4

 

5

 

6

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Non-Jumbo VLAN

Jumbo-Enabled VLAN

 

 

 

 

 

 

 

 

 

 

 

 

 

VLAN 10

 

 

 

 

 

 

 

 

 

 

 

 

 

 

VLAN 20

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Port 3 belongs to both VLAN 10 and VLAN 20. Jumbo frames received inbound on port 3 can be forwarded out the Non-Jumbo ports 4, 5, and 6.

Figure 12-4. Forwarding Jumbo Frames Through Non-Jumbo Ports

Jumbo frames can also be forwarded out non-jumbo ports when the jumbo frames received inbound on a jumbo-enabled VLAN are routed to another, non-jumbo VLAN for outbound transmission on ports that have no memberships in other, jumbo-capable VLANs. Where either of the above scenarios is a possibility, the downstream device must be configured to accept the jumbo traffic. Otherwise, this traffic will be dropped by the downstream device.

12-10