| reply to swintec
Re: Remaining Florida Markets All CMTS Chassis like the Cisco UBR the Motorolla BSR the ADC/BigBand Cuda have routing tables. The IP Address of the CPE (home computer or router), when it comes on line is granted an entry in the forwarding table....meaning this machine with this known good IP address is sending data in and that data needs to be forwarded correctly.
Now, an IP address is actually a logical assignment by some human effort. Machines care less about what IP address they have, machines really work via the MAC hardware address of the NIC Card or Ethernet port.
The MAC forwarding table is the table that ties the IP Address of the CPE to the MAC Hardware address of the NIC card and associates it to the hardware port the CPE is connecting thru.
Your Home Computer also has a forwarding table, and it too is populated by IP addresses that are associated to MAC addresses. The protocol that handles association between "Logical" IP addressing and "Physical" MAC addressing is known as ARP or Address Resolution Protocol.
You can view your home computer forwarding table by opening a command prompt and typing the following command:
arp -a [ENTER]
Every single device that communicates via Ethernet will use the ARP protocol to maintain it's forwarding table. And the behavior of that forwarding table can be manipulated.
You can make STATIC or FIXED MAC address assignments, you can define how long an address is "live" in that table, in some cases you can even limit the size of the table.
On to the Modem....
The Modem, once it's registered, is little more than an "authorized" Docsis protocol bridge between the CMTS and the Home Computer. The home computer doesn't speak in Docsis, it speaks "Ethernet", but the Cable plant was built to conform to Docsis. This requires Docsis speaking devices at either end to do the translation so that the network "seems" like plain old ethernet to the home computer. I refer to the docsis bridging relationship between the CMTS and the Cable Modem.
So, yes, the Modem has an entry in the CMTS' MAC forwarding table, but it also has hardware address entries in Docsis specific tables on the CMTS as well. But aside from DHCP traffic every few days, the ONLY traffic directed at the modem, is Docsis "link" management,(T3, T4, ranging, you've seen these messages in Modem log posts) so the Modem itself, really doesn't communicate much with the CMTS at the IP addressing layer. |
