Chapter 17: IP Packet Filters, Subscriber Management
STANDARD Revision 1.0
C4® CMTS Release 8.3 User Guide
© 2016 ARRIS Enterprises LLC. All Rights Reserved.
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Where: the range of v6-max-cpe is 0-64, and 0 means "Do not allow any."
C4 CMTS Debug IP Packet Capture
The IP Packet Capture feature allows the user to select an existing IP filter and add an option to capture information about
incoming frames that match this particular filter. If the appropriate IP filter is not currently in the filter group, then a new
one can be added which will capture the desired packets. If the first filter in a group satisfies the matching conditions, then
it is the only one to match and the CMTS does not search any further. Functionality is identical for both US and DS IP filters.
Exercise caution when adding new IP filters: they may affect the actions of existing IP filters. When a new IP filter with a
lower index value is added to the group, it has priority over the filters with a higher index value. Therefore, whenever a
packet matches the new filter, the action of that filter will override the actions of those behind it. Likewise, if a filter is
added to the end of the list, i.e. it has a higher index value in a group, it can only match and take action if none of the filters
above it find a match.
Any number of IP filters can be set to capture information about the frames they are matching. All of the frame
information from all of the IP filters set to collect information is aggregated in the capture buffer. If too many IP filters are
enabled to capture frame data and there is heavy traffic load, some of the capture data is discarded.
The capturing of frame data occurs whenever an IP filter matches and its debug capture flag is set. This is true regardless of
how the IP filter’s Drop/Pass action is set.
The information captured by hardware and stored in a First In First Out (FIFO) buffer for each packet is called a capture
entry. A capture entry contains the following:
A capture entry header containing some information specific to this packet
Up to the first 100 Bytes of the captured packet.
This capture entry is read out of the FIFO by software so it can be parsed and reformatted to display as much or as little of
the gathered information as desired. Capturing the first 100 bytes of a packet provides sufficient information about
sources, destinations, and protocols. The capture entry header reveals where the match physically occurred, and can be
used to reference count information associated with the IP filter and group that matched. It also provides trigger function
type, channel ID, and other pertinent information.
There is no software limit to the number of IP filters that can be enabled for packet capture. All IP filters could be triggering
packet captures. There is however a practical limit as to how many flows can be monitored and how much traffic can be
passed from the hardware up to the software. This limit is difficult to define since it is based on several variables.
