Quick Reference Guide

PowerConnect B-Series TI24X Configuration Guide 621
53-1002269-02
Configuring IP parameters – Layer 2 Switches
21
When the stamped DHCP discovery packet is then received at the router, it is forwarded to the
DHCP server. The DHCP server then extracts the gateway address from each request and assigns
an available IP address within the corresponding IP subnet (Figure 104). The IP address is then
forwarded back to the workstation that originated the request.
NOTE
When DHCP Assist is enabled on any port, Layer 2 broadcast packets are forwarded by the CPU.
Unknown unicast and multicast packets are still forwarded in hardware, although selective packets
such as IGMP, are sent to the CPU for analysis. When DHCP Assist is not enabled, Layer 2 broadcast
packets are forwarded in hardware.
NOTE
The DHCP relay function of the connecting router must be turned on.
FIGURE 104 DHCP Offers are forwarded back toward the requestors
DHCP
Server
Hub
207.95.7.6
Router
Host 1
Host 2
Host 3 Host 4
192.95.5.x
Subnet 1
200.95.6.x
Subnet 2
202.95.1.x
Subnet 3
202.95.5.x
Subnet 4
Interface 2
Interface 14
Interface 8
Step 1:
DHCP IP address requests
for Hosts 1, 2, 3 and 4 in
Subnets 1, 2, 3 and 4.
Gateway addresses:
192.95.5.1
200.95.6.1
202.95.1.1
202.95.5.1
Step 2:
The switch stamps each DHCP request
with the gateway address of the
corresponding subnet of the
receiving port.
Step 3:
Router forwards the DHCP request to the
server without touching the gateway
address inserted in the packet by the switch.
Layer 2 Switch