Netgear XCM8806 Chassis User Manual - Page 620

NETGEAR 8800 User Manual Proxy ARP Between Subnets In some networks, it is desirable to configure the IP host with a wider subnet than the actual subnet mask of the segment. You can use proxy ARP so that the router answers ARP requests for devices outside of the subnet. As a result, the host communicates as if all devices are local. In reality, communication with devices outside of the subnet are proxied by the router. For example, an IP host is configured with a class B address of 100.101.102.103 and a mask of 255.255.0.0. The switch is configured with the IP address 100.101.102.1 and a mask of 255.255.255.0. The switch is also configured with a proxy ARP entry of IP address 100.101.0.0 and mask 255.255.0.0, without the always parameter. When the IP host tries to communicate with the host at address 100.101.45.67, the IP host communicates as if the two hosts are on the same subnet, and sends out an IP ARP request. The switch answers on behalf of the device at address 100.101.45.67, using its own MAC address. All subsequent data packets from 100.101.102.103 are sent to the switch, and the switch routes the packets to 100.101.45.67. IPv4 Multinetting IP multinetting refers to having multiple IP networks on the same bridging domain (or VLAN). The hosts connected to the same physical segment can belong to any one of the networks, so multiple subnets can overlap onto the same physical segment. Any routing between the hosts in different networks is done through the router interface. Typically, different IP networks are on different physical segments, but IP multinetting does not require this. Multinetting can be a critical element in a transition strategy, allowing a legacy assignment of IP addresses to coexist with newly configured hosts. However, because of the additional constraints introduced in troubleshooting and bandwidth, NETGEAR recommends that you use multinetting as a transitional tactic only, and not as a long-term network design strategy. The implementation introduced in XCM8800 is simpler to configure, does not require that you create a dummy multinetting protocol, and does not require that you create VLANs for each IP network. This implementation does not require you to explicitly enable IP multinetting. Multinetting is automatically enabled when a secondary IP address is assigned to a VLAN. The following sections discuss these multinetting topics: • Multinetting Topology on page 620 • How Multinetting Affects Other Features on page 621 • Configuring IPv4 Multinetting on page 626 • IP Multinetting Examples on page 626 Multinetting Topology For an IP multinetted interface, one of the IP networks on the interface acts as the transit network for the traffic that is routed by this interface. The transit network is the primary subnet 620 | Chapter 20. IPv4 Unicast Routing