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  • about multiple DHCP in Layer 3 Switch

    Hi ,

    One of my client is having a critical situation in there network. They do have only a single ISP Conection in their office. Now basically this is a hosting company and provide some virtual host to their clients.

    Now , here they are using 5 differant DC and about 100 Clients in each. Now they are using only a single isp connection ...so they are having a single outgoing gateway.

    So they want to implement a 5 Differant DHCP Server their network , which will be able to provide the ip configuration in each differant domain and their workstations which are the member of their own domain accordingly. but the question is that , they are using a single router and single outgoing gateway.

    Here is the configuation.

    DC1 : abc.com
    192.168.2.254
    255.255.255.0

    GW 192.168.2.1 ( Router IP )

    DNS 192.168.2.254
    4.2.2.2

    DC2 xyz.com

    192.168.2.253
    255.255.255.0

    GW 192.168.2.1 ( Router IP )

    DNS Config 192.168.2.253
    4.2.2.2

    Now they need each 5 dc need to be in seprate IP Subnet

    abc.com ( 192.168.2.x)
    xyz.com ( 192.168.3.x)

    but they all can use the same gw as 192.168.2.1 ( router IP )

    So can we implement this scenario using a L3 Switch...and how to implement. Do we need to create per port own DHCP ?

    please help...

    Thanks...

    Kathy....

  • #2
    Re: about multiple DHCP in Layer 3 Switch

    You setup your vlans on the switch. Create your SVI's (Layer 3 interfaces for each vlan) on the layer 3 switch. Each vlan will have their own ip subnet. Setup your dhcp pools. Setup any filtering between the vlans. Set your clients in each vlan to use the default gateway of the corresponding vlan SVI. Since they all use the same internet gateway you will have to add those new ip subnets to your nat config etc...

    Also tell them to get some redundancy. You say that they are a hosting company? What hosting company has so many single points of failure?
    CCNA, CCNA-Security, CCNP
    CCIE Security (In Progress)

    Comment


    • #3
      Re: about multiple DHCP in Layer 3 Switch

      Hi ,

      Thanks for your reply ...

      So basically its possible with Layer 3 switch ..only i need to create the seprate vlan on each port and create dhcp server on each port and for outside internet traffice i can use the same gateway router IP ...

      Here is the things...

      vlan 1 : 192.168.1.x /24

      gw 192.168.1.1

      DHCP Pool : 192.168.1.50 - 192.168.1.100

      vlan 2 192.168.2.x /24

      gw 192.168.1.1

      DHCP Pool : 192.168.2.50 - 192.168.2.100

      vlan 3 192.168.3.x /24

      gw 192.168.1.1

      dhcp pool 192.168.3.50 - 192.168.3.100


      so is this type of design is possible with layer 3 switch...

      Also please provide me the steps to configure this...

      Thanks,

      Kathy

      Comment


      • #4
        Re: about multiple DHCP in Layer 3 Switch

        Configuration depends on the make/model of the layer 3 switch. I suggest you consult the configuration guide for your product. You could put the dhcp pools on the switch but I would use a dedicated dhcp server for that.
        CCNA, CCNA-Security, CCNP
        CCIE Security (In Progress)

        Comment


        • #5
          Re: about multiple DHCP in Layer 3 Switch

          Hi ,

          Thanks for your reply ,

          I am in plan to purchase a Cisco L3 Switch ..what are your suggestion , which is model is easy to configure for end user with clear GUI Options available.

          Also , what do you mean to say by creating a dedicated DHCP Server , i mean is there any software DHCP Server available in Market , which creates a DHCP server for 10 different subnet and use a single outgoing gateway....

          please help...

          Thanks,

          Comment


          • #6
            Re: about multiple DHCP in Layer 3 Switch

            How much money are you willing to part with? The new Cisco 3750X's are expensive. You may be able to pickup a used older 3750 on ebay for about $500.00 US for a 48 port. Configuration would depend on how comfortable you are with using the command line. The gui for enterprise level cisco switches is pretty lackluster as they assume you know how to use the CLI to configure them. Good part is that all Cisco products are well documented.

            A windows dhcp server can handle 10 dhcp scopes with ease. The gateway has nothing to do with the dhcp server directly. The server will hand out the proper addresses and gateways to your clients as long as you pools are configured correctly and the dhcp helper is configured correctly on the L3 switch SVI's.
            CCNA, CCNA-Security, CCNP
            CCIE Security (In Progress)

            Comment


            • #7
              Re: about multiple DHCP in Layer 3 Switch

              Hi ,

              Can you please explain more on making a windows DHCP Server , with 10 different scope inside with differant IP Subnet...and use a same outgoing gateway...

              please help...

              Thanks...

              Comment


              • #8
                Re: about multiple DHCP in Layer 3 Switch

                Not sure where your lost? A dhcp request is a broadcast. A dhcp server can have multiple dhcp scopes and serve clients on different subnets. Since dhcp is a broadcast by default, broadcasts are not forwarded by layer 3 interfaces. A way around this is to turn the broadcast from the client into a unicast from the layer 3 device. Using the ip helper command on your switch's layer 3 SVI interfaces will allow the SVI to take that broadcast and convert it to a unicast and forward the request to the dhcp server.

                How does the dhcp server know what scope to pull the address from? Well it uses the giaddress field in the request from the dhcp relay agent (in your case the svi on that particular subnet). That way a client on one subnet will get the proper address from dhcp along with the proper default gateway for its subnet.

                I suggest you lookup the DORA process for DHCP.

                DHCP (D)iscover
                DHCP (O)ffer
                DHCP (R)equest
                DHCP (A)ck
                Last edited by auglan; 2nd May 2013, 20:27.
                CCNA, CCNA-Security, CCNP
                CCIE Security (In Progress)

                Comment


                • #9
                  Re: about multiple DHCP in Layer 3 Switch

                  Originally posted by kathy View Post
                  Hi ,

                  Thanks for your reply ,

                  I am in plan to purchase a Cisco L3 Switch ..what are your suggestion , which is model is easy to configure for end user with clear GUI Options available.

                  Also , what do you mean to say by creating a dedicated DHCP Server , i mean is there any software DHCP Server available in Market , which creates a DHCP server for 10 different subnet and use a single outgoing gateway....

                  please help...

                  Thanks,
                  You won't be using a single default gateway for all of the clients. Each client will use the SVI in its VLAN/Subnet as its default gateway. the switch itself is the only device that needs the router as its default gateway.

                  Comment


                  • #10
                    Re: about multiple DHCP in Layer 3 Switch

                    Hi ,

                    So what will be the solution for my problem , I can not purchase individual router for all my schools

                    please help...

                    Thanks

                    Comment


                    • #11
                      Re: about multiple DHCP in Layer 3 Switch

                      I find it very hard to believe that you appear to be offering business services to your "clients" and you do not seem to have any basic understanding of their needs or possible solutions (let alone how to implement them). In this country, any business working like that would go bankrupt very quickly.

                      To attempt to help you solve this problem, can you give us more background information.
                      How many "schools"?
                      How are they connected to each other?
                      How are they connected to the internet?
                      What network hardware is available at each? (makes and models)
                      What servers are available at each?
                      What is your budget?
                      Tom Jones
                      MCT, MCSE (2000:Security & 2003), MCSA:Security & Messaging, MCDBA, MCDST, MCITP(EA, EMA, SA, EDA, ES, CS), MCTS, MCP, Sec+
                      PhD, MSc, FIAP, MIITT
                      IT Trainer / Consultant
                      Ossian Ltd
                      Scotland

                      ** Remember to give credit where credit is due and leave reputation points where appropriate **

                      Comment


                      • #12
                        Re: about multiple DHCP in Layer 3 Switch

                        Now its individual schools? You will need a layer 3 device at each location for routing. This could be a router or switch depending on the connectivity between sites, if nat is needed etc.
                        CCNA, CCNA-Security, CCNP
                        CCIE Security (In Progress)

                        Comment

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