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Ethernet Switch

New Contributor
Posts: 2
Registered: ‎02-23-2017
Accepted Solution

BCM53286 Unmanaged Mode with VLAN Tagging/Untagging

Is it possible to use the BCM53286 in Unmanaged mode and use the VLAN table Tagging/Untagging function?

There is the following note in the datasheet: "Note: When the device is operating in unmanaged mode, both the S-Tag modification instruction and the C-Tag modification instruction default to As Received. EVM is also disabled in unmanaged mode."

We are using the management port (24) as a normal network port connected to a microcontroller, to allow user configuration of our application via webpages, which allows configuration of the VLAN table Tagging/Untagging.

However the VLAN table configuration is ignored. If we change to managed mode the VLAN table configuration is now used and works, but we lose all the webpage functionality because the port 24 is now the IMP.

Is there a method that will allow us to use the VLAN table in Unmanaged mode?



Posts: 287
Registered: ‎02-15-2016

Re: BCM53286 Unmanaged Mode with VLAN Tagging/Untagging


For unmanaged mode, BCM5328x can not support IVM and EVM.

BCM5328x IMP port (management port 24) should be configured as managed mode for web management platform implementation.

Suggest could you use your BCM53286 Port 24 IMP port as the managed mode and your external microcontroller needs to handle the IMP tag when receive/transmit packets to BCM53286 IMP port?

Please double check IMP tag detail information described in "Frame Management" of Section 3 in datasheet.



New Contributor
Posts: 2
Registered: ‎02-23-2017

Re: BCM53286 Unmanaged Mode with VLAN Tagging/Untagging

Hi Ryan,

Thanks for the update.

I have changed to Managed Mode and added the IMP tag to the start of all ethernet frames sent from the CPU and adjusted the receive to expect the IMP tag and set the switch to receive Unicast, Multicast and Broadcast.

Using the following register values:

Page 0x00, Addr 0x00, Value 0x37 (managed mode)

Page 0x01, Addr 0x28, Value 0x47 (force 100M, full duplex, link up)

Page 0x01, Addr 0xA8, Value 0xDC (forwarding state, RX UC/MC/BC enabled)

Page 0x03, Addr 0x00, Value 0x80 (managed mode) also tried 0x81 and 0x83

All ethernet frames from the CPU to the Switch now have the IMP tag with: “OPCODE 1111: Indicates an IMP tagged packet to be forwarded and learned by the switch based on the normal switching flow” and all the remaining fields set to zero and the FCS adjusted accordingly.

The CPU now successfully receives all the packets from the Switch IMP and the received IMP tag is valid.

However, when the CPU transmits packets to the switch, they are not all being forwarded to the other ports. DCHP packets are sent, but ARP packets are not.

Monitoring the traffic with Wireshark shows the following:

CPU to Switch: DHCP Discover - Yes

Switch to CPU: DHCP Offer - Yes

CPU to Switch: DHCP Request - Yes

Switch to CPU: DHCP ACK - Yes

Switch to CPU: ARP Request - Yes

CPU to Switch: ARP Response - No

Following through the TCP/IP stack within the CPU, the ARP Response is being sent to the Switch IMP, but the Switch is not forwarding this to the other ports.

All subsequent ARP requests are received by the CPU from the Switch, but all the ARP responses sent from the CPU to the Switch are lost. We cannot successfully establish a TCP/IP connection.

Are there any other register settings that need to be changed?

For our application we need to be able to configure the switch with a webpage interface, from any browser – which works fine in Unmanaged Mode. However, we need to be able to use the VLAN tagging, which your previous post says is only supported in Managed Mode.



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