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Service Domain Features
Proxy ARP (Theory of Operation)
Scenario 1: Without Proxy ARP
2-2
Internet Control Management Protocol (ICMP)
In general, ICMP is supported. However, the options field is not reflected
back if the HotWire DSLAM is the destination address (i.e., the HotWire
DSLAM receives the data and then returns the packet without the options
field). The HotWire DSLAM does, however, pass the packet with the options
field to the next hop if the DSLAM is not specified as the destination address.
Dynamic Host Configuration Protocol (DHCP)
DHCP is the protocol used for automatic IP address assignment. A DHCP
discover or request message from an end-user system is transmitted over
DSL ports and forwarded to the designated DHCP server, which is typically
maintained and operated by the NSP for its address domain. The DHCP
server assigns an IP address to the end-user system. The HotWire RTU
routing tables and the DSLAM routing tables are automatically updated with
the IP address information by the DSLAM.
An Address Resolution Protocol (ARP) request is used to dynamically bind an IP
address to a MAC address. Proxy ARP is a technique by which a router answers
ARP requests intended for another machine by supplying its own MAC address
(also referred to as the physical address). By answering for another device, the
router accepts responsibility for forwarding packets to that device.
ARP is supported by the HotWire DSLAM and the HotWire RTU. Proxy ARP
allows the end users to appear to be directly connected to the router or VLAN
switch providing access to the NSP network. This is an advantage because
routers connected to a device running proxy ARP require less configuration. The
following scenarios show why this is an advantage.
In this scenario, Router B does not have proxy ARP software and the networks of
the default router (Router A) for workstation 1 (175.1.2.3) and workstation 2
(135.1.3.45) are different.
Router A
WS1
175.1.2.3
Workstation 1 (WS1) needs to send a packet to workstation 2 (WS2). For the
packet to arrive successfully at WS2:
There is a static route on Router A for WS2. The next hop is Router B and
the destination is WS2.
November 1997
LAN A
Router B
175.1.2.6
135.1.3.9
LAN B
WS2
135.1.3.45
97-15458-02
8000-A2-GB21-20
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