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Author Topic: DGS-1216T : MAC address filtering for the WebSmart interface?  (Read 6919 times)

frr

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DGS-1216T : MAC address filtering for the WebSmart interface?
« on: July 23, 2009, 04:17:16 AM »
I have a DGS-1216T running firmware 4.10.2.

I'm experimenting with the software bridge in Windows XP. If I run the Eth ports on the host PC without a bridge, I can connect to the DGS-1216T's HTTP interface just fine. If on the other hand I bridge the two interfaces, and I try to access the DGS-1216T's HTTP interface via the bridge, the TCP session seems to get connected, but no data ever gets through, I get no response to a HTTP GET command.

Makes me wonder how come? I get the IP address via DHCP. I always check that I've obtained one. Once I create the bridge, I can see STP (of the soft bridge) wait a few seconds, then one of the physical ports goes up and so does the virtual interface of the bridge, then it gets an address via DHCP. I can surf the internet, I can connect to any TCP ports in the local LAN (and the protocols over TCP work just fine). Only the DGS-1216T switches (two of them) don't want to serve HTTP to me when I'm running via the soft bridge.

The soft bridge seems to follow a specific algorithm when choosing a MAC address for its virtual network adapter: it takes the physical MAC address of one of the physical interfaces, and flips the first byte in the MAC address from "00" (general MAC address) to "02" (locally administered MAC address, I believe). Such as, it takes the 00-01-02-36-38-C3 of my 3com NIC and converts that into 02-01-02-36-38-C3. If one port is connected and the other one is not, the selection algorithm seems to favour the port that's not connected. The "locally administered" MAC address is the only difference that I've noticed, compared to the "separate ports / no bridge" configuration.

The XP soft bridge does produce some spanning tree packets, but I have STP disabled on all of my switches. Besides, bare Ethernet and TCP/IP connectivity seems to work fine against the DGS-1216T's management engine. It only doesn't respond over TCP. If I disable the "safeguard engine" in the switch, it doesn't help.

I am the IP / DHCP / Ethernet / DNS admin in my LAN...

This is certainly not a serious problem, rather an interesting quirk. I'm not rushing to update my firmware just to see if anything changes. Any ideas are welcome :-)
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