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Chapter 2
Cisco CMTS Configuration Commands
Command Modes
Cable interface configuration
Command History
Release
12.2(15)BC2
12.3(9a)BC
Usage Guidelines
Viruses, worms, and theft-of-service attacks can generate a large volume of ARP requests on a cable
interface. In some situations, the volume of ARP traffic can become so large that it throttles all other
traffic.
To control the number of ARP replies and ARP requests that are allowed for each SID on a cable
interface, use the cable arp filter command. This command configures the interface so that it accepts
only a certain number of ARP reply or request packets per a specified time period. If a SID generates
more ARP packets than what is allowed, the cable interface drops the excessive traffic.
By default, no ARP filtering is done. ARP filtering is enabled on individual cable interfaces, and you
can choose to filter ARP packets only on the specific cable interfaces that require it. You can further
choose to filter only ARP request packets, only ARP reply packets, or both. You can configure different
threshold values on each interface, allowing you to customize the feature for each interface's traffic
patterns.
If using bundled cable interfaces, the Cable ARP Filtering feature is configured separately on the master
and slave interfaces. This allows you to configure the feature only on the particular interfaces that require
it.
Disabling the cable ARP filtering feature, using the no cable arp filter command, does not reset the ARP
Tip
packet counters. The ARP packet counters do not increment when cable ARP filtering is disabled, but
the counters retain their current values until the interface counters are specifically cleared, using the
clear counters command.
Linksys Wireless-B BEFW11S4 Router
The Linksys Wireless-B Broadband Router BEFW11S4 version 4 with 1.44.2 firmware incorrectly sends
its own ARP reply packet for every ARP request packet it receives, instead of replying only to the ARP
requests that are specifically for itself. Customers with these routers should upgrade the firmware to the
latest revision to fix this bug. To upgrade the firmware, please go to the download section on the Linksys
web site, at the following URL:
http://www.linksys.com/Download
For the release notes for the latest revision of the firmware, see the following URL on the Linksys web
site:
http://www.linksys.com/download/vertxt/befw11s4v4_ver.txt
Examples
The following example shows how to filter cable ARP reply packets, so that the cable interface accepts
a maximum of 15 ARP replies every three seconds per SID:
OL-1581-08
Modification
This command was introduced for the Cisco uBR7246VXR and
Cisco uBR10012 universal broadband routers.
The values of number and window-size are optional for the the respetive
reply-accept and request-send settings.
Cisco Broadband Cable Command Reference Guide
cable arp filter
2-17
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