Multiple DHCP

how a dhcp client select a offer among offer from multiple dhcp server

Pankaj
It usually just accepts the first one. So if you have 2 ip helper-addresses under the vlan interface DHCP requests are sent to both DHCP server. Generally speaking the DHCP servers that replies first is the one used.
Jon

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NetBoot and Multiple DHCP Servers

Hey everyone,
We have a NetBoot machine running here at my school (where I work). It was working like a champ until a couple of weeks ago when our network got upgraded and there are now 2 DHCP servers on our network. That, for some reason, is totally screwing up our NetBooting process.
Here's what I think is happening, and maybe someone can tell me if I right or wrong. NetBoot (or BSDP protocol) is a "broadcast" protocol. (That means it's always just floating around out there on the network. ) NetBoot (BSDP) protocol gets injected into the DHCP stream, and any machine that gets DHCP can get BSDP, and essentially NetBoot.
The problem is with BSDP. BSDP protocol wants to have all of it's "broadcasts" come from the same server. So when we had 1 DHCP server, everything was fine, because client machines would get their whole NetBoot process from one machine... all of the BSDP broadcasts were coming from our 1 DHCP server.
Now, we have 2 DHCP servers. What happens is, a client will get some of it's BSDP broadcasts from one DHCP server, and some from another... which it does not like at all.
I recently read somewhere that it is possible to somehow make one of our DHCP servers the "authoritative" server, to which all of the clients will go to get their NetBooting info.
Does this sound in any way right? Are we on the right track ? Has anyone seen this before? Any help would be greatly appreciated. Thanks a million.
Mike

Now, we have 2 DHCP servers. What happens is, a
a client will get some of it's BSDP broadcasts from
one DHCP server, and some from another... which it
does not like at all.
Not unless your new DHCP server is also a NetBoot server and is set to provide NetBoot services. BSDP and DHCP are not the same thing. If what you were saying were true, it wouldn't be possible to have DHCP and NetBoot offered by different servers.
It IS possible, however, that the two DHCP servers are causing problems by both servicing DHCP requests for the same clients. If you've got multiple DHCP servers on the same subnet (or your router's configured to pass DHCP requests between subnets), you should make sure that only one of the DHCP servers answers requests from any given client. In our world, our Novell server is the default DHCP server on our subnet, but I keep a list of excluded MAC addresses on that server so that my Macintosh clients don't get addresses from it. On the Mac OS X server, I'm careful to limit my address ranges only to those machines which have static address maps in NetInfo. That way, our servers coexist, but they don't overlap.
It's not clear from your message whether your previously solitary DHCP server was your Mac OS X server, or whether one of the two DHCP servers is that box. But whatever the servers are, it might be helpful to turn off one of them to see if the same problem occurs (assuming you can, without major network disruptions). If that's not possible, can you talk to your network admins to see if there's some way to isolate your clients and one of the servers--in other words, see if there's some way to keep DHCP servers from responding to the same requests.
There may be any number of other reasons why this problem has cropped up. You may need to dust off a hub and a copy of Ethereal or EtherPeek to sniff what's happening on the network. You might also try NetBooting in verbose mode, to see where the process craps out. IIRC, there'a decent guide for this kind of troubleshooting over at Bombich's site (www.bombich.com).
Good luck.
David Walton

DHCP scope setings from multiple DHCP Servers

Is there any way to check any particular option is configured in all scopes from multiple DHCp servers.
for eg:- we would like to check if any scope has option 150 is configured in multiple DHCP servers.
I guess there are lots of cmdlets available from Win2k12 DHCP servers.
Regards, Nidhin.CK

Hi, Nidhin...
I use NETSH tool for this, can redirect results to file or filter w/ FIND.
Example:
NETSH dhcpserver \\SERVERNAME dump | FIND /I "set optionvalue 150"
Hope this helps!
Marcelo Lucas Guimarães - MCP, MCTS, MCDBA, MCITP Blog: http://mlucasg.wordpress.com

Multiple dhcp networks

Server OS:   OS X Mountain Lion Server
Thanks in advance for helping! I am trying to setup an OS X server to provide a DHCP address to systems using multiple DHCP networks.
I have previously only had to provide DHCP services for a single simple network like:   192.168.14.xx      (192.168.14.50 - 192.168.14.199)
Now that I need to provide DHCP for multiple networks like:    192.168.14.xx,   192.168.15.xx, and etc.
I am not sure how to make sure that the IP address provided is for the correct network.

There are two ways to do this. If you have a network at 192.168.14.0/24 and you want to add another class C 192.168.15.0/24 you can simply expand your network to a /23. This would give you a contiguous block of addresses from 192.168.14.1 through 192.168.15.254. Now technically, you are using a class C range but applying class b subnet. Regardless, it should work. If you need to expand beyond this then you end up with trouble. If your base network is 192.168.14.0 and you go to a /22 then the base is shifted down to 192.168.12.0/22. This may cause issues if you have a log of devices in the center of your 14 network.
The second option is to define VLans and tag them. This will require work on the switches, the creation of virtual interfaces on OS X and then the creation of DHCP ranges based on the VLan.
In this case, your 10.8 server can span the VLans and then server devices on each of them.
Reid
Apple Consultants Network
Apple Professional Services
Author "Mavericks Server – Foundation Services" :: Exclusively available in Apple's iBooks Store
Author "Mavericks Server – Control and Collaboration" :: Exclusively available in Apple's iBooks Store

WLC 5508 and Multiple DHCP servers in different sites?

Hi
I work for health authority in our region and we just purchased a Cisco wlc 5508 controller along with 25 3500 AP's. We have multiple sites with different IP subnets in each, all connected by a frame relay (owned by ISP). Each site has its own DHCP server. I have the controller in our main site. So when I take an AP to a remote site, the Ap gets an DHCP address from local DHCP server (which is great) and contacts controller and joins controller. Everything is good. BUT, when a client joins at the remote site, it gets an address from a previous site which will not work because the client is now on a different subnet. We dont use Vlans as they dont transvers the frame relay. I need those clients to obtain DHCP from the local DHCP server from the site they are on. Is that possible??
I have updated the controller to latest version as well.
Thanks
Bryan Yaciuk, CCNA
Parkland Regional Health Authority

We call this as HREAP LOCAL SWITCHING!! but here is the catch.. everytime the AP joins the new site.. we need to configure the VLAN mapping and this wil do it for you!! Here is the link which will resolve ur issue..
http://www.cisco.com/en/US/tech/tk722/tk809/technologies_configuration_example09186a00807cc3b8.shtml#ll
Lemme know if this answered ur question and please dont forget to rate the usefull posts!!
Regards
Surendra

Multiple DHCP on Multiple VLAN not working

Hi there;
In my core network switch, I have multiple VLANs, I have these command to assign to DHCP pools. I configured a port on my core switch for DMZ_VLAN and when I connect my computer to this port, I can get the ip address from the dmz_vlan dhcp pool. Because I assigned an IP address to the interface of vlan 192, then I found that one of my server "192.168.0.100" connection dropped, I cannot ping this server on the dmz VLAN, and it cannot provide the http service as usual until I remove the "interface vlan 192" from the switch. Why? However; without this command, I cannot receive the 192.168.0.0 network IP from the pool.
ip dhcp pool data_vlan1
network 10.10.1.0 255.255.255.0
default-router 10.10.1.1
dns-server 10.10.1.100 10.10.1.101
domain-name company.local
lease 7
ip dhcp pool dmz_vlan
network 192.168.0.0 255.255.255.0
default-router 192.168.0.1
dns-server 8.8.8.8 4.2.2.2
domain-name company.com
lease 7
interface vlan 10
ip address 10.10.1.254
interface vlan 192
ip address 192.168.0.254

Sorry for the delay as I got busy with work. If your layer 3 switch is the default gateway for VLAN 192 then the default-router for the DHCP scope should be the IP address of the layer 3 switch interface (192.168.0.254). With that being said, the FW DMZ_192 interface, the switch SVI for VLAN 192 and the DMZ server should all be in the same broadcast domain, thus they should be able to reach each other.
So, can you confirm with me exactly what does not work on the server configured with VLAN 192 and a static IP? For instance,
1. Can you ping the server from the L3 switch
2. Can you ping the server from the FW
3. Can the server ping 192.168.0.1 and 192.168.0.254
4. Can the server ping the outside world? For instance, www.google.com and 4.2.2.2
5. Have you tried taking a test PC, connecting to the switchport configured for VLAN 192 and see if you get an IP address from the DHCP scope

WLC Controllers with Multiple DHCP Servers

Hello All,
I have a central office with (2) 4402 WLC's and about 25 Branch offices throughout the country. Currently all AP's are static IP'd with IP's from the local Branch office subnets. However the Clients all pull their IP's from a Central DHCP server here at corporate.
What I would like to do, is have clients get local branch office IP's from the AP located at that site. So rather than using a central DHCP server here at corporate using a single subnet for all wireles clients. Clients would be assigned local IP's by preferably local DHCP servers. I am having trouble finding an answer to this problem within the documentation. Any help or Ideas would be appreciated.

were not using any radius type authentication. But I am still a bit hazy on how the hreap thing works, I did read the link and it is very helpful but I was kind of thrown into this one without much wireless background. Right now when I change an Ap to H-reap it somehow disables the a radio. I cant seem to get that back working which im not all that sure is even that big of a deal. The SSID is configured for local switching and central auth.

Multiple DHCP Subnet through V lan

Dear All,
i like to request a help, i am not good in cisco anyone can explain me it will help for me.
i am trying to configure muliple dhcp subent through Valn
1. i create a dhcp server and create 3 subetnet
a. my network card ip 192.168.50.200 dhcp enabled
b . configure DHCP scope for 192.168.20.0 and 192.168.30.0
2. i have sonicwall firewall with router there i create 2 valn .
3. cisco switch sg300-28p also create valn. ( valn 20 port 3-5) (Vlan 30 port 7-10) create a trunk port for both Vlan port number 2.
i give conection from sonicwall to switch trunk port 2 and connect laptop to valn 20 port i am getting 192.168.20.0 range ip, if i connect to laptop to Vlan 30 also getting Vlan 30 range IP.( this time Sonicwall DHCP is enabled)
now come to the point, i need to relase DHCP from my server, so i disable dhcp from Sonicwall. and enable dhcp from server.
but i am not getting ip address from server to any valn.
i create a trunk port for DHCP server and connect to there. then also same problem
please help to configure the best way.

what you have to do is configure ip helper addresses on your vlans to point to the new server, it was probably pointing to your sonicwall which is why it was working on the sonicwall, but once you changed over to your server, you have to convert it over to your new dhcp server.
without port forwarding your switches/routers do not know where to send those requests, especially if they are on different vlans. thats one ceveat to running vlans and switches, it doesnt like flooding out requests to every port.
it appears to be under:
ip config - udp relay/ip helper
that section, add your new dhcp server to that and it should fix it so it sends your dhcp requests to your dhcp server.

Multiple DHCP scopes on WLC 5508 (not showing leases?)

I have 2 DHCP scopes set up on a wlc 5508, one for the AP's and another for a wlan, the leases for the AP's scope show up, but the one that the clients on the WLAN are on do not show up in the "show leases" is that a bug? normal?

Customers using Cisco Unified Wireless solutions have been reporting issues with the DHCP support provided on the Wireless LAN Controller (WLC). Some of these issues are software bugs or debugability problems. Others are due to lack of proper understanding on the DHCP implementation.
This document describes the different DHCP operations on the wireless controller, which provides consistent and accurate information to customers in an effort to reduce the related customer issues and TAC cases.
Please refer to the following link: http://www.cisco.com/c/en/us/support/docs/wireless/4400-series-wireless-lan-controllers/110865-dhcp-wlc.html

3000 series and Multiple DHCP scopes (DHCP-relay)

I need to send different DHCP options to users; however, I need to put certain groups in different subnets. Is it possible to setup the concentrator to relay for addresses from different scopes?

- Configuration
- System
- IP Routing
- DHCP Relay
a. Enable 'Enabled' checkbox
b. Select Forward to
c. Address == 192.168.10.8 255.255.255.0
- Address Management
- Assignment
a. Enable 'Use DHCP'
- User Management
- Groups
- Select 'groupA'
- Modify Group
- Click General tab
- Enter 'DHCP Network Scope' x.x.x.x
- Select 'groupA'
- Remove Address Pool
Now I get the following error:
118 02/08/2005 13:29:00.720 SEV=3 DHCPDBG/39 RPT=34
DHCP discover timeout: no response from polled servers (xid 3821297335)
I can ping the server, and it is serving up this scope to other devices (just not from the concentrator)

Multiple DHCP servers Not authorized to start in domain.

Hello all,
Suddenly in our network, we started noticing that DHCP servers are getting unauthorized automatically and stop servicing to their clients.
it is happening randomly to all my locations and post restarting the service and authorize the service will solve the issue.
I dont know why this behavior and still some dhcp servers are prompting with this issue.
Upon checking the evenlog, i am able to find that the event id "1046" with the error message loggind in those machines stating that
The DHCP/BINL service on the local machine, belonging to the Windows Administrative domain CORP.DRREDDYS.COM, has determined that it is not authorized to start. It has stopped servicing clients. The following are some possible reasons for this:
This machine cannot reach its directory service enterprise and it has encountered another DHCP service on the network belonging to a directory service enterprise on which the local machine is not authorized.
Please provide your inputs on this behavior.
Regards,
Andrew

Could anybody update on this cause.

Multiple DHCP servers

Hi gurus,
I have DTUs on shared networks. Each network has a Cisco 2610 router running the DHCP Relay.
Because on these networks there are also some PCs other than DTUs, I would DHCP Relay sets different DHCP server IPs for DTUs from PCs. PCs should get/refer to a general DHCP server, while DTUs should get/refer to the SRS DHCP.
Do you know if it is possible?
MTIA

Hi,
Why should you use a separate server for Sun Ray DTU's. Keep your setup as
simple as possible and that is perfectly possible with Sun Ray.
Just use your DHCP server that you use for your PC environment and start
your Sun Ray server with "utadm -L on" (which does not setup a DHCP
server on your Sun Ray server).
Still Sun Ray DTUs like to know the SR specific information. To provision these,
have a look at:
http://blogs.sun.com/ThinkThin/entry/sun_ray_provisioning
I have best experiences with option 66 in the standard DHCP server and .parms file.
Jaap

Multiple DHCP Subnets for different Interfaces

Hi All,
Lets Assume that I have a 1841 single WAN and 2 Fast Ethernet ports.
I have 2 different Local LANs, one on each FastE.
Fast 0/0 : LAN 1
Fast 0/1 : LAN 2
Lets say i want to assign IP Addresses from the router acting as a DHCP.
I know how to set it up for single interface.
Lets say I want for :
Fast 0/0 - LAN 1 :192.168.1.0/24
Fast 0/1 - LAN 2 :192.168.2.0/24
How do i specify on the router what IP Range belongs to which interface ???, so that each interface will give out to its connected LAN the desired IP Addresses ???
Thanks,
George

Hi,
Its just that you have to configre two pools for DHCP.
When a request is generated by the PC it will send a DHCP broadcast message with the source IP as 0.0.0.0. When this reaches the interface it will change the source IP address to its own IP address and will send a unicast dhcp request to the DHCP server. This way based on the interface's IP address the request will be matched with one of the defined pool and the client will be assigned the IP address from the respective pool.
There is a good link which will explain this in detail-
http://tcpmag.com/qanda/article.asp?EditorialsID=285
Sushil

Netgear WC7600 Best Practise Multiple DHCP / VLAN

We are coming to this with a background in setting up Cisco wireless controllers and the question is specifically in relation to management of...

Hi
Reinstalling a WS709TP after doing factory reset. Physical installation fine, all APs provisioned. However pretty much all the advanced config...

DHCP pools for LWAP's with multiple models

I have 2 different AP models (1130's & 1140's) for which I want to create a DHCP pool on a core layer 3 switch with an Option 43 pointing to the Wireless LAN Controller. In conjunction with the Option 43 entry however, I need to specify the AP type as an ASCII string in the Option 60 parameter. Problem is, how can this be done for multiple ASCII strings; ie. multiple AP models? The DHCP pool option 60 entry only allows for one string and you can only enter one option 60 command per DHCP pool. Surely it is common to have more than one AP model and that this can be done without having to resort to multiple DHCP pools (one for every model)?
Can anyone shed some light on this for me please? Would be much apprciated as I've come up blank on CCO documentation!

I usually just stage the AP first to join a WLC and to make sure it works prior to installing it. Pllace it on the same submnet as the management and let it join and then set the primary, secondary and or tertiary. Then you can move it to any vlan you want. If you want to use DHCP Option or DNS, then you should know that if for example it is an RCVK IOS previous to capwap it will only do LWAPP. Once it joins to the WLC in LWAPP it takes a new IOS the unit will do CAPWAP.
As an example 1140 have an RCVK IOS that only run CAPWAP, so it should only do CAPWAP:
CISCO-LWAPP-CONTROLLER and CISCO-CAPWAP-CONTROLLER
Create two A records both pointing to the same controller if you want to use DNS.
DHCP Option 43:
DHCP Option 43 is limited to one access point type per DHCP pool. You must configure a separate DHCP pool for each access point type.
http://www.cisco.com/en/US/docs/wireless/access_point/1140/quick/guide/ap1140getstart.html#wp37440

Multiple DHCP

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