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TRUNKed VLANs & DHCP

martin.law
Level 1
Level 1

I want to configure each port on a Cat 3548 to be configured as a separate subnet & VLAN and then trunked together on port 1 using a 2621 router. The second port on the 2621 connects the the rest of the network where the DHCP server exists. Each port on the 3548 will be connected to a hub where the PCs work. Will this work ? Will DHCP be forwarded correctly to the PCs.

The aim of all this is so that is easy to identify which PCs are conected to which hubs.

I should explain that the hubs are sited between 3 & 8 km from the 3548 via fibre & media converters.

2 Replies 2

rfroom
Cisco Employee
Cisco Employee

You will need to configure an "ip helper-address on each sub-interface for each vlan to forward the DHCP requests. See the following document for more details:

http://www.cisco.com/warp/public/473/100.html

cpurdy
Level 1
Level 1

In addition to ip helpler, you may need to enable spanning-tree portfast on each port so the DHCP request does not time out. I have had this happen when DHCP server is across the WAN.

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