DHCP & BOOTP design problem
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Thread: DHCP & BOOTP design problem

  1. #1
    Senior Member
    Join Date
    Nov 2002
    Posts
    382

    Question DHCP & BOOTP design problem

    I'd like to sollicite the good knowledge of AOs.

    My problem:
    I'd like to assign IP address basing on the interface on which the the client request is coming to the router. I can't think that's not achievable but does anyone confirm?
    This may be a very simple issue for some of ya; please help!

    I quickly read the RFC951 but I can't find an answer.

    Details:
    The network is basically composed by a switch, a router & a DHCP server as follow:
    Code:
                                          -------------
                                          | Router  |___________DHCP Server
                                          -------------
                                                   |
                                                   |  802.1q trunk
                                                   |             
                              ___________________
                              |              Switch                |
                              |  ______           ______ |
                              |  |VLAN1|          |VLAN2| |
                              |  -----------          ----------  |
                              --------------------------------
                                     |                         [
                                host 1                host2
    With 802.1q logical/virtual interface the router sees 2 bridge-group & subnets.
    The router performs bootp to mediate DHCP request to the server.
    The router may be CISCO or Linux or whatever that's an open issue.

    My goal is to configure the IP of "host 1" into the associated VLAN subnet just using the fact that BootP knows on which logical port it receives the request!

    ouf!

    Thanx to guys that have been through all of this!
    [shadow] SHARING KNOWLEDGE[/shadow]

  2. #2
    Member
    Join Date
    Mar 2003
    Posts
    99
    Well if your running 802.1q then you should be able to set up multiple sub interfaces on your router for each VLAN on the switch. That way each VLAN basically has it's own DHCP segment

    Example Config:
    ROUTER

    interface FastEthernet3/0
    no ip address
    speed 100
    full-duplex
    !
    interface FastEthernet3/0.1
    description Wireless_and_MGMT
    encapsulation dot1Q 1 native
    ip address 10.0.30.252 255.255.255.0
    ip helper-address 10.0.30.245
    ip helper-address 10.0.60.244
    no ip redirects
    standby 1 ip 10.0.30.254
    standby 1 priority 110
    standby 1 preempt
    !
    interface FastEthernet3/0.400
    description 3rd Floor
    encapsulation dot1Q 400
    ip address 10.0.29.252 255.255.255.0
    ip helper-address 10.0.30.245
    ip helper-address 10.0.60.244
    no ip redirects
    ip pim sparse-mode
    standby 2 ip 10.0.29.254
    standby 2 priority 110
    standby 2 preempt
    !
    interface FastEthernet3/0.401
    description Secondary_Building_LAN
    encapsulation dot1Q 401
    ip address 192.168.0.41 255.255.255.252
    no ip redirects
    !
    interface FastEthernet3/0.402
    description 1st Floor
    ip address 10.0.27.252 255.255.255.0
    ip helper-address 10.0.30.245
    ip helper-address 10.0.60.244
    no ip redirects
    standby 3 ip 10.0.27.254
    standby 3 priority 110
    standby 3 preempt
    !
    interface FastEthernet3/0.403
    description 2nd Floor
    encapsulation dot1Q 403
    ip address 10.0.28.252 255.255.255.0
    ip helper-address 10.0.30.245
    ip helper-address 10.0.60.244
    no ip redirects
    standby 4 ip 10.0.28.254
    standby 4 priority 110
    standby 4 preempt

    SWITCH CONFIG
    set vlan 1 name default type ethernet mtu 1500 said 100001 state active
    set vlan 400 name Dallas_Wired_Users-10.0.29 type ethernet mtu 1500 said 100400 state active
    set vlan 401 name 302_Street-192.168.0.40 type ethernet mtu 1500 said 100401 state active
    set vlan 402 name 302_1st_Floor type ethernet mtu 1500 said 100402 state active
    set vlan 403 name 302_2nd_Floor type ethernet mtu 1500 said 100403 state active

  3. #3
    Senior Member
    Join Date
    Jan 2002
    Posts
    458
    If the router is a cisco, you should be able to use an IP helper address, no?

  4. #4
    Senior Member
    Join Date
    Nov 2002
    Posts
    382
    Thanx d0ppelg@nger, but does not the IP helper just redirect DHCPDISCOVER to the remote DHCP Server (IPhelper=BootP=DHCP Relay or whatever?).

    The DHCP server decide the assigned host IP. How does he know in which subnet it should allocate the IP.
    Let's take an example: Host belongs to your FastEthernet3/0.400 subnet. The router will forward the DHCPDISCOVER to the DHCP thanx to the BOOTP protocol.
    During that exchange of BOOTP there must be some info about the subnet the host belons to, isn't it?
    [shadow] SHARING KNOWLEDGE[/shadow]

  5. #5
    Member
    Join Date
    Mar 2003
    Posts
    99
    The DHCP server will hand out IP Address from the range that the request came from. Example, If a user's system boots up and it's on the 400 VLAN, which is the FastEthernet3/0.400 segment. The DHCP server will see the requst coming from 10.0.29.252. It will then respond with an IP from the 10.0.29 network in it's DHCP table. DHCP handles the requests, you just have to set up the segments on the router and switch, and add the DHCP segments in your DHCP server. It'll be handled automatically.

  6. #6
    Senior Member
    Join Date
    Nov 2002
    Posts
    382
    d0ppelg@nger wrote:
    The DHCP server will hand out IP Address from the range that the request came from. Example, If a user's system boots up and it's on the 400 VLAN, which is the FastEthernet3/0.400 segment. The DHCP server will see the requst coming from 10.0.29.252. It will then respond with an IP from the 10.0.29 network in it's DHCP table. DHCP handles the requests, you just have to set up the segments on the router and switch, and add the DHCP segments in your DHCP server. It'll be handled automatically.
    Of course that's obvious.
    You opened my eyes when I was blind.

    Thanx buddy
    [shadow] SHARING KNOWLEDGE[/shadow]

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