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Cisco uBR7200 Series Universal Broadband Router Software Configuration Guide
OL-2239-03
Chapter3 Configuring Cable Modem Interface Features
Configuring Cable Subinterfaces
no cable proxy-arp
cable downstream annex B
cable downstream modulation 64qam
cable downstream interleave-depth 32
cable downstream symbol-rate 5056941
cable upstream 0 frequency 15008000
no cable upstream 0 shutdown
Tip If you are having difficulty with verification, make sure that you entered the correct port and cable
interface line card slot number when you activated cable proxy ARP.
Activating Packet Intercept Capabilities
To activate packet intercept functionality, use the following commands in cable interface configuration
mode.
Configuring Cable Subinterfaces
The command to create a subinterface over a cable interface is the same as that defined by Cisco IOS for
other software applications:
interface cable x/y.n
where x is the slot number, y is the port number, and n is the subinterface number.
Each created subinterface is assigned a software IDB. The layer 3 packet arriving over a physical cable
interface must be assigned an appropriate software IDB to which it belongs. Since each packet that is
received over a cable interface is prepended with its associated SID, this can be extracted from the packet
and used as the key to find the associated software IDB. The defined cmts_sid_instance_t structure holds
information pertaining to the SID and is extended to include the associated software IDB pointer.
The IP address stored in the DHCP reply is matched for its subnet value against the subnet value
configured for each of the subinterfaces over the physical cable interface. The subnet information is
derived by combining the IP address and the mask value available in the software IDB structure.
The linked list of software IDBs can be accessed from the hardware IDB associated with the physical
cable interface. At the time of CM registration, the software IDB address is initialized to null as the
mapping is unknown at first.
Tip In current releases of software, the SID-to-subinterface mapping is done based on the DHCP-assigned
IP address and is not user configurable.
Subinterface Configuration Example
The following example shows how to define a subinterface on the cable5/0:
interface cable5/0
! No IP address
! MAC level configuration only
Command Purpose
Router(config-if)# cable intercept
xxxx.xxxx.xxxx
Specifies a MAC address on the cable network for which
interception capabilities are to be activated. There is a
limit of 10 MACs.
Router(config-if)# no cable intercept
xxxx.xxxx.xxxx
Disables interception after it is enabled.