Components of the Network Model
4-4
8000-A2-GB21-20
November 1997
Proxy ARP
Proxy ARP is supported by the DSL cards and the HotWire 5446 RTU. It allows
the end users to appear to be directly connected to the router 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.
DSL Card Proxy ARP
When an ARP request is sent by an NSP connected to the DSL card 10BaseT
interface for a downstream end-user system (one on the same IP network), the
DSL card will proxy ARP for the ES. The following figure shows the packet flow
when the NSP wants to send a packet to the ES.
97-15470-02
Local Router
155.1.2.1/
255.255.255.0
155.1.3.1/
255.255.255.0
NSP
155.1.2.2/
255.255.0.0
DSL Card
155.1.3.2/
255.255.255.0
RTU
135.1.3.3
Local Router: ARP Request for ES
Local Router: Sends packet to DSL
card, which forwards it to ES
DSL: Proxy ARP (for ES)
ES
155.1.3.4
NSP: Sends packet to
Local Router
In this illustration:
The local router receives the IP packet and does an ARP request for the ES.
The DSL card receives the broadcast ARP request. The DSL card does an
ARP reply for the ES by replying with its own MAC address. Addresses for
which the DSL card will proxy ARP must be configured as part of static route
configuration. See the
HotWire DSLAM for 8540 and 8546 DSL Cards User’s
Guide for more information.
When the local router receives the ARP reply, it sends the packet to the DSL
card, and the DSL card forwards it to the ES.
NOTE:
In certain network configurations, the use of proxy ARP on the DSL cards will
cause HP OpenView to log a major event. This will happen since HP
OpenView received the same IP address from two different MAC addresses.
By default, the HP OpenView system logs and displays all events. However,
you may elect to filter specific unwanted events. Instructions on how to filter
out these events are dependent on the release of HP OpenView/Netview that
you are running. For detailed instructions, see the appropriate HP OpenView
user documentation.
