Port Status and Basic Configuration

Jumbo Packets on the Series 2800 Switches

■When a port is not a member of any jumbo-enabled VLAN, it drops all jumbo traffic. If the port is receiving “excessive” inbound jumbo traffic, the port generates an Event Log message to notify you of this condition. This same condition generates a Fault-Finder message in the Alert log of the switch’s web browser interface, and also increments the switch’s “Giant Rx” counter.

■If you do not want all ports in a given VLAN to accept jumbo packets, you can consider creating one or more jumbo VLANs with a membership comprised of only the ports you want to receive jumbo traffic. Because a port belonging to one jumbo-enabled VLAN can receive jumbo packets through any VLAN to which it belongs, this method enables you to include both jumbo-enabled and non-jumbo ports within the same VLAN. For example, suppose you wanted to allow inbound jumbo packets only on ports 6, 7, 12, and 13. However, these ports are spread across VLAN 100 and VLAN 200, and also share these VLANs with other ports you want excluded from jumbo traffic. A solution is to create a third VLAN with the sole purpose of enabling jumbo traffic on the desired ports, while leaving the other ports on the switch disabled for jumbo traffic. That is:

 

VLAN 100

VLAN 200

VLAN 300

Ports

6-10

11-15

6, 7, 12, and 13

Jumbo-

No

No

Yes

Enabled?

 

 

 

 

 

 

 

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 packets 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 packets can forward them to the ports in the VLAN that do not have jumbo capability.

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