Chapter 15: Interface IP Configuration
STANDARD Revision 1.0
C4® CMTS Release 8.3 User Guide
© 2016 ARRIS Enterprises LLC. All Rights Reserved.
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Multiple subinterfaces may be defined per physical port and associated with the same VRF, such that there is a many-to-
one relationship between subinterfaces and VRFs, per cable-side physical interface. The C4/c CMTS system administrator
must also be allowed to change the association between a subinterface and a VRF.
The default VRF is the global VRF that is always present in the C4/c CMTS. It can neither be created nor destroyed. Note
that upon creation of a subinterface, it is implicitly associated with the default VRF.
The relationship of a subinterface to a VRF is many-to-one when viewed from the perspective of a single CAM physical
interface or cable bundle. Each ingress cable-side IP packet must classify to one and only one subinterface. This
classification to a subinterface will be based solely on the source IP address and source physical port of the packet. For
broadcast DHCP packets that have a source IP address of 0.0.0.0, the following rules apply:
If the DHCP packet is sourced from a CM, then the packet will classify to the lowest numbered subinterface that has a
DHCP-Server defined.
If the DHCP packet is sourced from a CPE, then the packet must be classified to the subinterface of the CPE’s associated
CM.
Rules of Operation and Guidelines for Subinterfaces
The C4/c CMTS supports up to 150 IPv4 interfaces (both interfaces and subinterfaces count towards the total of 150).
A subinterface is associated with the default VRF upon creation.
The sum of all subinterface IP addresses may not exceed the total C4/c CMTS system limitation of 1000 IPv4 interfaces.
This limit represents all primary and secondary IP addresses associated with each subinterface.
The following items may be provisioned per subinterface:
IP addresses, both primary and secondary
DHCP Relay Agent including: primary/policy mode selection, secondary dhcp-giaddr identification, DHCP Lease
Query (cable source verify) functionality and DHCP Server IP address definitions
IP filter groups
Directed broadcast support
RIP and OSPF
IGMP
IRDP (ICMP Router Discovery Protocol)
SCM access