Cisco uBR10012 Software Configuration Manual page 81

Chapter 1 Overview of Cisco uBR10012 Universal Broadband Router Software
Host-to-Host Communication (Proxy Address Resolution Protocol)
Proxy Address Resolution Protocol (ARP) allows the Cisco uBR10012 router to issue ARP requests on
behalf of CMs on the same cable network subnet. Proxy ARP can help machines on a subnet reach
remote subnets without configuring routing or a default gateway.
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Hosts have no idea of the physical details of their network and assume it to be a flat network in which
they can reach any destination simply by sending an ARP request. But using ARP for everything has
disadvantages, some of which are listed below:
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For configuration information, refer to
Integrated Time-of-Day Server
This operational feature allows theCisco uBR10012 router to respond to time-of-day (ToD) (RFC 868)
queries from cable interfaces during the registration process. For information about configuring DHCP,
ToD, or TFTP services, refer to the chapter titled "Configuring DHCP, ToD, and TFTP Services" in the
Cisco Cable Modem Termination System Feature
PBR support for the Cisco uBR10012
Policy-Based Routing (PBR) provides a tool for expressing and implementing the forwarding or routing
of data packets, on the basis of the policies that are defined by network administrators. PBR allows
policy override on routing protocol decisions by selectively applying policies based on access list and/or
packet size.
Network administrators can also use PBR to selectively change the IP ToS, IP precedence, and IP QoS
Group fields for matching incoming packets on an interface.
The Cisco uBR10012 universal broadband router supports a maximum of 255 PBR policies and 32 route
maps within each policy. The following subset of policy-based routing commands is supported in Cisco
IOS release 12.2(11)CY:
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OL-1520-05
The Cisco router's interface should be configured to accept and respond to proxy ARP.
The workstation must be configured to view the entire network as a single network. This is typically done
by configuring the workstation with a smaller subnet mask than the network really uses.
The router replies to the proxy ARP request with its MAC address. Therefore, the workstation sends all
traffic for this destination address to the router, and the router forwards it according to the routing table.
This method increases the amount of ARP traffic on your segment.
Hosts need larger ARP tables to handle IP-to-MAC address mappings.
Security may be undermined. A machine can claim to be another in order to intercept packets, an
act called "spoofing."
ARP does not work for networks that do not use ARP for address resolution.
ARP does not generalize to all network topologies (for example, more than one router connecting
two physical networks).
ip policy route-map map-tag
route-map map-tag [permit | deny] [sequence-number]
match ip address {ACL-number | ACL-name} [ACL-number | ACL-name ...]
match length min max
set [default] interface type number [type number ...]
set ip [default] next-hop ip-address [ip-address ...]
set ip precedence value
set ip qos-group value
Supported Software Features for the Cisco uBR10012 Router
"Activating Cable Proxy ARP Requests" section on page
Guide on Cisco.com.
Cisco uBR10012 Universal Broadband Router Software Configuration Guide
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