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FastIP reduces the load on routing devices when VLANs are implemented on your network.
This chapter explains more about the concept of FastIP and how it is enabled on your Switch. It covers the following topics:
FastIP is a system that allows you to use the IEEE 802.1Q VLAN standard to reduce the load on routing devices when VLANs are implemented on your network.
Endstations within different VLANs can only communicate using a routing device; if there is a large amount of inter-VLAN traffic, the router can become overloaded and network performance can be affected. FastIP allows your endstations and Switch units to find secure short cuts for inter-VLAN traffic that bypass the routing device altogether.
When using FastIP, you must have a routing device (router or Layer 3 switch) in your network. In addition, we recommend that:
All your Switch units have FastIP enabled. Note, however, that the FastIP system does work if:
All your endstations support FastIP. For more information, refer to the user documentation supplied with your endstations or the Network Interface Card (NIC) of your endstations.
FastIP works as follows:
1 . If an endstation A supports FastIP, it determines whether each data packet is being sent to a local endstation (one in the same VLAN) or a remote endstation (one in another VLAN).
2 . If endstation A is about to send a data packet to a remote endstation B, it sends a special NHRP (Next Hop Resolution Protocol) packet to endstation B. This packet contains the MAC address and VLAN membership details of endstation A.
3 . The NHRP packet passes through the Switch units to the routing device, and back through the Switch units to endstation B.
4 . If endstation B supports FastIP, it records the MAC address and VLAN membership of endstation A.
5 . Endstation B sends an NHRP packet with its own details back to endstation A. This packet, however, is sent directly through the Switch units and not through the routing device. To do this, endstation B specifies that:
6 . Endstation A receives the NHRP packet from the endstation B and records the MAC address and VLAN membership of endstation B.
7 . Endstation A sends the data packet to endstation B directly through the Switch units. To do this, endstation A specifies that:
Figure 38 (overleaf) shows a network containing two endstations, three Switch units and a routing device. Endstation A is in VLAN 1, and endstation B is in VLAN 2. In this setup, FastIP is not enabled and if endstation A sends data packets to endstation B they must pass through the routing device.
If FastIP is enabled on the Switch units and endstations:
1 . Endstation A sends an NHRP packet to endstation B through Switch A, Switch C, the routing device, Switch C, and Switch B. This is shown in Figure 39.
2 . When endstation B receives the NHRP packet from endstation A, it sends its own NHRP packet to endstation A through Switch B, Switch C and Switch A. This is shown in Figure 40.
3 . When endstation A receives the NHRP packet from endstation B, it sends data packets to endstation B through Switch A, Switch C and Switch B - without passing through the routing device. This is shown in Figure 41.
Figure 38 Network without FastIP
Figure 39 Endstation A sends an NHRP packet to endstation B
Figure 40 Endstation B sends an NHRP packet to endstation A
Figure 41 Endstation A sends data packets to endstation B
By default, the Switch Database of a Switch is divided by VLAN - each VLAN has an independent area of the database. With this system, the Switch Database can store an entry for a device in several VLANs at the same time, and the entry for a particular VLAN can be stored against different ports. As an example, Figure 42 illustrates the Switch Database storing an entry for endstation A in VLANs 1, 2 and 3, and the entries are all stored against port 1.
Figure 42 Entry stored in multiple VLANs
Figure 43 illustrates the Switch Database storing an entry for endstation A in VLANs 1, 2 and 3 - here, the VLAN 1 entry is in port 1, the VLAN 2 entry is in port 2, and the VLAN 3 entry is in port 3.
Figure 43 Entry stored in multiple VLANs, each entry in a different port
When FastIP is used by the Switch, the Switch Database can no longer be divided by VLAN - it must be shared by all the VLANs. Although the VLANs are still operational, this creates two limitations:
To enable FastIP on your Switch or stack:
1 . From the web interface, click the Configuration icon on the side-bar.
2 . Click the Advanced Stack Setup hotlink. The Advanced Stack Setup page is displayed.
3 . From the FastIP listbox, select Enabled.
4 . Click the Apply button.
CAUTION: If you change the setting of the FastIP listbox, the Switch or stack needs to be reset before the change comes into effect.
If FastIP is enabled, IEEE 802.1Q learning is also enabled automatically. For more information about IEEE 802.1Q learning, see "Using IEEE 802.1Q Learning".