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Multicast MAC problem

                   Hello,

We have in one of our remote sites (whcih is connected using IPVPN network from our provider to the main site) a PLANET media converter which we are using it to connect to a power meter to get readings through Serial RS-232 VirtualCom from the main site.

The MAC address for this media converter is starting with 45xxxxxxx which is a multicast address.

First of all, we couldn't reach that media converter IP address from the main site PING or HTTP MGT access, but we can reach it from the LAN at that remote site. I contacted the ISP in order to add a static ARP entry at the CPE at that remote site and after that static ARP entry adedd i can reach it from the main site.

Now, our problem is when that media converter power loss and re-power on again (or restarted) i can't access it remotely from the main site unless i go to that remote site and connect my laptop LAN there and do a PING from my laptop, after that i can reach it remotely.

Any ideas?

thanks in advance

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Cisco Employee

Multicast MAC problem

Hello,

Is it possible for you to disclose the entire MAC address?

I suspect a problem with devices on the path towards the media converter learning/accepting the multicast MAC address. It is outright wrong and illegal for a device to use a multicast MAC address as its own address. Such constellation can never be expected to work and no workarounds are guaranteed to have a lasting effect. Switches and even routers may refuse to accept such address as a valid station's MAC address. I am pretty sure that for example Catalyst switches will not learn a multicast MAC address on their switchports even if placed into the SourceMAC address field of an Ethernet frame - they will merely complain about an occurence of an invalid source MAC address.

In addition, issues with delivering multicast frames may also complicate things (such as IGMP Snopping or similar).

The bottom line is: if the media converter's MAC address is indeed a multicast MAC address then you should try to find a way how to modify it - perhaps it can be reconfigured to a normal individual MAC address.

One question, though: is it perhaps possible that the device has a different individual MAC address and is just configured to listen on this additional multicast 45... MAC address?

Best regards,

Peter

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