User`s guide

Components of the Network Model
4-7
8000-A2-GB21-10
June 1997
MCC Card Proxy ARP
Proxy ARP is also supported by the MCC card. In a HotWire DSLAM network
configuration, when an ARP request is sent by a device (such as a router) to the
MCC card’s 10BaseT interface to resolve either the DSL card or HotWire 5446
MAC address, the MCC card will proxy ARP for those devices so long as their IP
addresses are on the same network (135.1.3.x). The MCC card responds to
these ARP requests with its own MAC address (proxy ARP). Incoming packets
are then forwarded to that appropriate DSL card across the HotWire DSLAM
system backplane.
The following illustration shows the packet flow when the DCE Manager wants to
send a packet to the HotWire 5446 RTU.
97-15465-01
Local Router
135.1.1.2/16
135.1.2.1/24
135.1.3.254
DCE
Manager
135.1.1.1/16
MCC Card
e1a:135.1.2.2/24
s1b:135.1.3.1/24
DSL Card
s1b:135.1.3.2/24
RTU
135.1.3.3
Local Router:
ARP Request for RTU
Local Router: Sends packet to
RTU via the MCC and DSL cards
MCC: Proxy ARP (for RTU)
DCE Manager:
Sends packet to
Local Router
In this illustration:
 The local router does an ARP request to resolve the HotWire 5446 MAC
address.
 The MCC card is in the same network (135.1.3.1). It sees the ARP request.
The MCC card knows that the HotWire 5446 is downstream, because it
contains a route to it (generally a host route). The MCC card does an ARP
reply for the HotWire 5446 by responding with its own MAC address.
 When the local router receives the ARP reply, it forwards the packet to the
MCC card.
 After receiving the packet, the MCC card forwards it to the DSL card which
forwards it to the HotWire 5446 RTU.