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Ask the Expert- SD-WAN


Is DHCP Possible on 2500 Series Routers

Hello everyone. I'm currently studying for my CCNA certification. I would like to incorporate 2500 series router to my existing network. My network has a DHCP server and DNS server. My goal is to add 2500 series router to my existing network and play around with backing up the router configuration using a TFTP server. I know the commands to perform task, but my issue is I can't put 2500 series router on same subnet as my existing network.

My plan is simple, I want 2500 series router to connect to my ISP router connected via Ethernet cable to AUI port using a 10Base-T Transceiver. Then I'll use available port eth0 on 2500 router to connect to my Cisco switch that feeds my entire network. I want to implement this plan so all devices connected to my network have Internet access, therefore using the router as a gateway to access Internet. On 2500 series router I tried making port eth0 DHCP and did not allow me to do so, then I tried making ports Serial0, and Serial1 DHCP and would not allow me. Is DHCP allowed on 2500 series routers? If so what are the commands to a port DHCP?

Is there a way to make 2500 series router a gateway to access the Internet? For example, Ideally I want ISP router to connect to 2500 router either through eth0 or Serial, then connect next available port whether its eth0 or serial0/serial1 to Cisco switch to provide Internet access to entire network.  

Everyone's tags (1)
Hall of Fame Master

Thank you for having the

Thank you for having the diagram of the network which helps to make clear what you want to accomplish. Am I correct in assuming that the ISP router uses an Ethernet to connect to your network? There is one important thing which you have not yet told us and that is how many Ethernet interfaces does this 2500 have? Some of the 2500 have two Ethernet and some have only one Ethernet (and may have a Token Ring or extra Async or other type interface). If you have only a single Ethernet then I do not believe that you will be able to accomplish what you have described. If the ISP router uses an Ethernet connection and your switch uses an Ethernet connection then your 2500 will need to have two Ethernet connections.




When I run the command show

When I run the command show ip interface brief, it displays

Router1#show ip interface brief

Interface            IP-Address     OK?   Method Status  Protocol

Ethernet0          x.x.x.x               YES   manual up         up

Serial0              unassigned      YES   unset                 administratively down down

Serial1              unassigned      YES   unset                 administratively down down


I currently have ISP cable router connected to 2500 router via Ethernet. On router, I currently have Ethernet0 connected to ISP router. What is the purpose of having Serial0 and Serial1 for?

I thought maybe I can use serial connections as Ethernet ports, it's my understanding I can't. I know I can add an IP address to serial connections, but not make serial ports DHCP. I know my router is out-dated and doesn't offer the flexibility I need.

My next step is to purchase a faster router that provides more than 10MB/s throughput. I'm thinking about purchasing a Cisco 2801 router that has two Ethernet ports.

Thank you for taking the time to answer my question.

Hall of Fame Master

Your 2500 has a single

Your 2500 has a single Ethernet and so will not allow you to connect to the ISP router and to the switch. You will need a router with two Ethernets (or two FastEthernets) to accomplish your connections.

The serial interfaces on the router are to enable you to connect the router to some other device that has serial connections. If you go back in time some years it was very common to use serial links for Wide Area connections and Ethernet for Local Area connections. In more recent times it is common to use Ethernet for both WAN and LAN connections.

While some serial interfaces use RJ45 connectors like Ethernet does, the serial connections are a significantly different technology than Ethernet. It does not work to connect an Ethernet on one device to a serial on another device.



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