How Multinetting Affects Other Features - Extreme Networks ExtremeWare XOS Guide Manual

IP Multinetting
Figure 57: Multinetted Network Topology
Transit
VLAN multi
network
Primary subnet
Secondary
Host
subnet-1
Secondary
subnet-2
BD10K
EX_102
Figure 57 shows a multinetted VLAN named multi. VLAN multi has three IP subnets so three IP
addresses have been configured for the VLAN. One of the subnets is the primary subnet and can be
connected to any transit network (for example, the Internet). The remaining two subnets are stub
networks, and multiple hosts such as management stations (such as user PCs and file servers) can be
connected to them. You should not put any additional routing or switching devices in the secondary
subnets to avoid routing loops. In Figure 57 the subnets are on separate physical segments, however,
multinetting can also support hosts from different IP subnets on the same physical segment.
When multinetting is configured on a VLAN, the switch can be reached using any of the subnet
addresses (primary or secondary) assigned to VLAN. This means that you can perform operations like
ping, Telnet, Trivial File Transfer Protocol (TFTP), Secure Shell 2 (SSH2), and others to the switch from a
host residing in either the primary or the secondary subnet of the VLAN. Other host functions (such as
traceroute) are also supported on the secondary interface of a VLAN.

How Multinetting Affects Other Features

Multinetting will affect some other features in ExtremeWare XOS. The following sections explain how
multinetting affects both Layer 2 and Layer 3 features.
ARP
ARP operates on the interface and responds to every request coming from either the primary or
secondary subnet. When multiple subnets are configured on a VLAN and an ARP request is generated
by the switch over that VLAN, the source IP address of the ARP request must be a local IP address of
the subnet to which the destination IP address (which is being ARPed) belongs.
For example, if a switch multinets the subnets 10.0.0.0/24 and 20.0.0.0/24 (with VLAN IP addresses of
10.0.0.1 and 20.0.0.1), and generates an ARP request for the IP address 10.0.0.2, then the source IP
address in the ARP packet will be set to 10.0.0.1 and not to 20.0.0.1.
373
ExtremeWare XOS 11.1 Concepts Guide