Hi Guys,
I am in process of investigating some issues in our environment with DOCSIS Cable Modem.
After packet capturing it was found the following behaviour:
Let's say we have two cable modem connected to the same CMTS (Cisco uBR 7225) using the same MAC Domain and sharing the same L3 network. CMTS behaves as following:
1. CM1 wants to communicate with CM2
2. As they are in the same subnet CM1 sends ARP request
3. This ARP requests comes to CMTS, CMTS generates another ARP requests in which Source MAC is changed to its one (CMTS)
4. New ARP requests comes to CM2, CM2 replies to CMTS
5. CMTS receives the APR Reply and generates new one with Source MAC address of CMTS and sends to CM1
It seems CMTS behaves like ARP proxy but:
1. ARP proxy is not enabled on CMTS and area of applying this feature is not that we have in this simple setup
2. CMTS is not changing ARP header, it just changes L2 header. If this is expected that CMTS is re-sending its own ARP requests but not forward the original one (that comes from CM1) ?
Whether CMTS behavior is OK in this case?
Thank you in advance.
