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Chapter 9
Management Network Connectivity
Figure 9-3
IP Address 192.168.1.20
Subnet Mask 255.255.255.0
ARP matches higher-level IP addresses to the physical addresses of the destination host. It uses a lookup
table (called the ARP cache) to perform the translation. When the address is not found in the ARP cache,
a broadcast is sent out on the network with a special format called the ARP request. If one of the
machines on the network recognizes its own IP address in the request, it sends an ARP reply back to the
requesting host. The reply contains the physical hardware address of the receiving host. The requesting
host stores this address in its ARP cache so that all subsequent datagrams (packets) to this destination
IP address can be translated to a physical address.
Proxy ARP enables one LAN-connected ONS 15600 to respond to the ARP request for ONS 15600s that
are not connected to the LAN. (ONS 15600 Proxy ARP requires no user configuration.) For this response
to occur, the DCC-connected ONS 15600s must reside on the same subnet. When a LAN device sends
an ARP request to an ONS 15600 that is not connected to the LAN, the gateway ONS 15600 returns its
MAC address to the LAN device. The LAN device then sends the datagram for the remote ONS 15600
to the MAC address of the proxy ONS 15600. The proxy ONS 15600 uses its routing table to forward
the datagram to the non-LAN ONS 15600.
9.2.4 Scenario 4: Default Gateway on CTC Computer
Scenario 4 is similar to Scenario 3, but Nodes 2 and 3 reside on different subnets, 192.168.2.0 and
192.168.3.0, respectively
CTC computer to communicate with Nodes 2 and 3, you would enter Node 1 as the default gateway on
the CTC computer.
Scenario 3: Using Proxy ARP
CTC Workstation
IP Address 192.168.1.100
Subnet Mark at CTC Workstation 255.255.255.0
Default Gateway = N/A
ONS 15600 #2
Default Router = N/A
Static Routes = N/A
(Figure
9.2.4 Scenario 4: Default Gateway on CTC Computer
ONS 15600 #1
IP Address 192.168.1.10
Subnet Mask 255.255.255.0
Default Router = N/A
Static Routes = N/A
SONET RING
9-4). Node 1 and the CTC computer are on subnet 192.168.1.0. For the
Cisco ONS 15600 Reference Manual, R7.0
LAN A
ONS 15600 #3
IP Address 192.168.1.30
Subnet Mask 255.255.255.0
Default Router = N/A
Static Routes = N/A
9-5
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