Scenario 3: Using Proxy Arp To Enable An Ons 15327 Gateway; Figure 4-3 Scenario 3: Using Proxy Arp - Cisco ONS 15327 User Documentation

Chapter 4 IP Networking

4.2.3 Scenario 3: Using Proxy ARP to Enable an ONS 15327 Gateway

Scenario 3 is similar to Scenario 1, but only one ONS 15327 (node #1) connects to the LAN
Two ONS 15327s (#2 and #3) connect to ONS 15327 #1 through the SONET DCC. Because all three
ONS 15327s are on the same subnet, Proxy ARP enables ONS 15327 #1 to serve as a gateway for ONS
15327s #2 and #3.
Figure 4-3
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 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 15327 to respond to the ARP request for ONS 15327s not
connected to the LAN. (ONS 15327 Proxy ARP requires no user configuration.) For this to occur, the
DCC-connected ONS 15327s must reside on the same subnet. When a LAN device sends an ARP request
to an ONS 15327 that is not connected to the LAN, the gateway ONS 15327 returns its MAC address to
the LAN device. The LAN device then sends the datagram for the remote ONS 15327 to the MAC
address of the proxy ONS 15327. The proxy ONS 15327 uses its routing table to forward the datagram
to the non-LAN ONS 15327.
June 2002
Scenario 3: Using Proxy ARP
CTC Workstation
IP Address 192.168.1.100
Subnet Mask 255.255.255.0
Default Gateway = N/A
ONS 15327 #2
Default Router = N/A
Static Routes = N/A
ONS 15327 #1
IP Address 192.168.1.10
Subnet Mask 255.255.255.0
Default Router = N/A
Static Routes = N/A
SONET RING
Cisco ONS 15327 User Documentation, R3.3
ONS 15327 IP Addressing Scenarios
(Figure
LAN A
ONS 15327 #3
IP Address 192.168.1.30
Subnet Mask 255.255.255.0
Default Router = N/A
Static Routes = N/A
4-5
4-3).