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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Loopback Interfaces for Routing Protocols
This section deals with the RSM loopback interface that may be used by OSPF. This interface has all the characteristics of a
physical interface IP address, including packet counts, admin provisioning, socket-layer accessibility, and so on. This new
interface type has a presence on the SCM when in-band management is enabled.
Automatic import of the loopback interface into the SCM protocol stack is consistent with existing in-band management
functionality. Currently, all RSM-based interface IP addresses are imported into the SCM to allow SCM-based applications
to process traffic destined for one of the C4/c CMTS interface IP addresses. Packet redirection from the RCM to the SCM is
a hardware decision based on the IP packet type.
Characteristics of the Loopback Interface
Observe the following guidelines when configuring and administering loopback interfaces:
The C4/c CMTS supports 64 unique loopback interfaces, ranging from 0-63.
The subnet mask must be /32; this implies a host address.
Upon creation of a loopback interface, it will be associated with the default VRF.
If the loopback is taken down, no physical interface is taken out of service (OOS).
If OSPF is enabled on the loopback interface, the network associated with the loopback address must be advertised in a
router LSA. The existing OSPF command must be used:
network <ip address> <mask> area <areaId>
Like physical interfaces, a loopback may reside in only one area.
Routing protocols (RIPv2, ISIS, OSPFv2, or BGP) will not advertise the active IP address.
The active IP address will not have a presence on the RCM.
When in-band management is enabled, loopback interfaces associated with the default VRF are imported into the
SCM’s protocol stack.
If multiple loopback interfaces exist, the lowest value loopback interface is used as the source IP address for SCM-
originated IP datagrams.