user manual

12-4
Cisco ONS 15454 SDH Reference Manual, R5.0
April 2008
Chapter 12 CTC Network Connectivity
12.2.3 Scenario 3: Using Proxy ARP to Enable an ONS 15454 SDH Gateway
Figure 12-2 Scenario 2: CTC and ONS 15454 SDH Nodes Connected to Router
12.2.3 Scenario 3: Using Proxy ARP to Enable an ONS 15454 SDH Gateway
ARP matches higher-level IP addresses to the physical addresses of the destination host. It uses a lookup
table (called an 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 15454 SDH to respond to the ARP request for
ONS 15454 SDH nodes that are not connected to the LAN. (ONS 15454 SDH proxy ARP requires no
user configuration.) The DCC-connected ONS 15454 SDH nodes must reside on the same subnet. When
a LAN device sends an ARP request to an ONS 15454 SDH that is not connected to the LAN, the
gateway ONS 15454 SDH returns its MAC address to the LAN device. The LAN device then sends the
datagram for the remote ONS 15454 SDH to the MAC address of the proxy ONS 15454 SDH. The proxy
ONS 15454 SDH uses its routing table to forward the datagram to the non-LAN ONS 15454 SDH.
CTC Workstation
IP Address 192.168.1.100
Subnet Mask 255.255.255.0
Default Gateway = 192.168.1.1
Host Routes = N/A
Router
IP Address of interface “A” to LAN “A” 192.168.1.1
IP Address of interface “B” to LAN “B” 192.168.2.1
Subnet Mask 255.255.255.0
Default Router = N/A
Host Routes = N/A
ONS 15454 SDH #1
IP Address 192.168.2.10
Subnet Mask 255.255.255.0
Default Router = 192.168.2.1
Static Routes = N/A
ONS 15454 SDH #2
IP Address 192.168.2.20
Subnet Mask 255.255.255.0
Default Router = 192.168.2.1
Static Routes = N/A
ONS 15454 SDH #3
IP Address 192.168.2.30
Subnet Mask 255.255.255.0
Default Router = 192.168.2.1
Static Routes = N/A
LAN B
LAN A
Int "A"
Int "B"
SDH RING
96709