DHCP conflict

I am running 10.4 server in an elementary school with about 100 computers, desktops and laptops, mostly running 10.4. The server was set up by a professional in the summer to run DHCP. A week or so ago, we lost our internet connection. It seemed the trouble was our sonic wall content filter so it was disconnected and the router reconfigured (not by me) to do DHCP. Now we have internet but it drops all the time. Clicking renew DCCP lease solves the problem but I assume there is a conflict between the server and the router. I tried disabling DHCP in the server and the router separately but we lost service again completely? Does anyone have any thoughts for a new person?

There isn't enough information here to be able to form an opinion, or at least, answer the question.
There are so many ways the network could be architected that it's hard to tell.
For example, what services (other than DHCP) is the server providing? Just directory service? file service? web service?
Is it acting as a gateway providing network service to the clients (so all clients talk through the server)?
That's important to know since it will affect how the clients connect.
In general, it shouldn't matter which DHCP server manages the network (and multiple DHCP servers are valid, too), provided they are configured appropriately.
You should really think about what your preference is - do you want the Mac to provide DHCP, or the router?
Once you decide that you can focus on configuring that device in the way that's appropriate for your network and disable the other completely.

Similar Messages

Auto clear ip dhcp conflict *?

Is there a command or config that will make a router automatically clear ip dhcp conflict * on a regular basis? I have a site that constantly has a problem with DHCP due to conflicts which is fixed simply by clearing the conflict table. If we could automate this, it would be great.

I modified your example to solve similar issue. I wanted it run every hour though. Here's how to modify Cron format:
https://en.wikipedia.org/wiki/Cron#Predefined_scheduling_definitions
My EEM simple script:
DV-CORE(config)#event manager applet ClearDHCP
DV-CORE(config-applet)#event timer cron cron-entry "0 * * * *"
DV-CORE(config-applet)#action 1.0 cli command "enable"
DV-CORE(config-applet)#action 2.0 cli command "clear ip dhcp conflict *"
DV-CORE(config-applet)#action 3.0 cli command "clear ip dhcp binding *"

DHCP Conflict Detection & Win 7 Firewall..

       This may be a stupid question, but I can't quite find the answer....
   We have a small network, about 200 computers (Server 2012), Win 7 workstations (Very Few XP's left)
I had one workstation detect an IP conflict (XP if it makes any difference), and it just was assigned another address
and it was on its merry way.   I took a look at the DHCP server and realized that I never turned on DHCP Conflict detection.
I turned it on and set it for 1 attempt.
    So for the heck of it I pinged the workstation and DNS worked but ping is blocked on the workstations firewall.
    Which made me wonder if I should push out a GP to allow ping to all the workstations???? (Question 1)
     Question two: If I do that to all the workstations, what would stop it from happening if someone brings a "guest"
     laptop into the building??
           What would be best options? or is it working as it should and I am just Paranoid!! LOL
                           Thank You in advance for any advice
                                           Wolverine..

Hi,
According to
this article, Client computers running Windows Server 2008, Windows Vista, Windows Server 2003, Windows XP, Windows 2000, Windows NT 4.0, Windows Millennium Edition, and Windows 98 automatically check to determine if an IP address is already in use before
using it. I think this behavior still exists in windows server 2012.
On the server-side, when a DHCP client requests a lease, a DHCP server checks its pool of available addresses and assigns the client a lease on an available IPv4 address. By default, the server checks only the list of current leases to determine whether an
address is available. It doesn’t actually query the network to see whether an address is in use. If you enable address conflict detection, the DHCP server uses the ping process to test available scope IP addresses before including these addresses in DHCP lease
offers to clients.
In addition, each additional conflict detection attempt delays the DHCP server response by a second while waiting for the ping request to time out. This increases the load on the server, so it is not recommended to set the value greater than two for ping attempts.
Hope this helps!
Best regards,
Susie

DHCP conflict due to Gratuitous ARP.

One of my wireless VLAN DHCP scope on cisco core switch is often exhausted due to Gratuitous ARP.
Please help me to check what is the cause of this.

I have a VLAN with DHCP SCOPE and layer 3 configured on core switch.
the DHCP pool often gets exhausted and when I do show ip dhcp conflict most of the IPs conflicted due to Gratuitous arp
CORESWITCH# show ip dhcp conflict
172.28.106.195 Gratuitous ARP Oct 14 2014 04:44 PM
172.28.106.54 Gratuitous ARP Oct 14 2014 04:49 PM
172.28.106.189 Gratuitous ARP Oct 15 2014 12:28 PM
172.28.106.55 Gratuitous ARP Oct 17 2014 02:05 PM
172.28.106.74 Gratuitous ARP Oct 21 2014 09:39 AM
172.28.106.72 Gratuitous ARP Oct 23 2014 02:26 PM
172.28.106.89 Gratuitous ARP Oct 28 2014 03:09 PM
172.28.106.119 Gratuitous ARP Nov 03 2014 01:39 PM
172.28.106.124 Gratuitous ARP Nov 05 2014 08:03 AM
172.28.106.127 Gratuitous ARP Nov 05 2014 02:56 PM
172.28.106.131 Gratuitous ARP Nov 08 2014 01:59 PM
172.28.106.153 Gratuitous ARP Nov 10 2014 12:14 PM
172.28.106.139 Gratuitous ARP Nov 11 2014 07:57 AM
172.28.106.143 Gratuitous ARP Nov 11 2014 09:28 AM
172.28.106.157 Gratuitous ARP Nov 11 2014 02:36 PM
172.28.106.156 Gratuitous ARP Nov 11 2014 07:55 PM
172.28.106.162 Gratuitous ARP Nov 13 2014 06:48 PM
172.28.106.187 Gratuitous ARP Nov 18 2014 01:57 PM
172.28.106.176 Gratuitous ARP Nov 19 2014 02:30 PM
172.28.106.53 Gratuitous ARP Nov 19 2014 02:47 PM
172.28.106.199 Gratuitous ARP Nov 20 2014 11:18 AM
172.28.106.61 Gratuitous ARP Nov 20 2014 01:27 PM
172.28.106.56 Gratuitous ARP Nov 20 2014 01:39 PM
172.28.106.63 Gratuitous ARP Nov 21 2014 02:15 PM
172.28.106.85 Gratuitous ARP Nov 24 2014 07:17 PM
172.28.106.92 Gratuitous ARP Nov 25 2014 10:47 AM
172.28.106.95 Gratuitous ARP Nov 25 2014 02:14 PM
172.28.106.97 Gratuitous ARP Nov 27 2014 04:19 PM
172.28.106.100 Gratuitous ARP Nov 28 2014 09:18 AM
172.28.106.79 Gratuitous ARP Nov 28 2014 11:09 AM
172.28.106.104 Gratuitous ARP Nov 28 2014 05:20 PM
172.28.106.129 Gratuitous ARP Dec 01 2014 09:53 AM
172.28.106.130 Gratuitous ARP Dec 01 2014 11:19 AM
172.28.106.133 Gratuitous ARP Dec 01 2014 11:36 AM
172.28.106.134 Gratuitous ARP Dec 01 2014 03:04 PM
172.28.106.135 Gratuitous ARP Dec 01 2014 03:47 PM
172.28.106.136 Gratuitous ARP Dec 01 2014 04:13 PM
172.28.106.137 Gratuitous ARP Dec 02 2014 12:28 PM
172.28.106.141 Gratuitous ARP Dec 03 2014 09:33 AM
172.28.106.149 Gratuitous ARP Dec 05 2014 02:01 PM
172.28.106.151 Gratuitous ARP Dec 05 2014 04:21 PM
172.28.106.173 Gratuitous ARP Dec 08 2014 06:40 PM
172.28.106.182 Gratuitous ARP Dec 09 2014 09:28 AM
172.28.106.158 Gratuitous ARP Dec 09 2014 04:46 PM
172.28.106.185 Gratuitous ARP Dec 09 2014 05:05 PM
172.28.106.188 Gratuitous ARP Dec 10 2014 02:56 PM
172.28.106.186 Gratuitous ARP Dec 10 2014 06:19 PM
172.28.106.193 Gratuitous ARP Dec 12 2014 12:48 PM
172.28.106.75 Gratuitous ARP Dec 16 2014 02:37 PM
172.28.106.68 Gratuitous ARP Dec 16 2014 04:05 PM
172.28.106.80 Gratuitous ARP Dec 16 2014 06:02 PM
172.28.106.81 Gratuitous ARP Dec 17 2014 03:11 PM
172.28.106.84 Gratuitous ARP Dec 19 2014 02:03 PM
172.28.106.115 Gratuitous ARP Dec 23 2014 10:35 AM
172.28.106.78 Gratuitous ARP Dec 23 2014 01:37 PM
172.28.106.121 Gratuitous ARP Dec 24 2014 06:18 PM
172.28.106.125 Gratuitous ARP Dec 26 2014 10:02 AM
172.28.106.161 Gratuitous ARP Dec 29 2014 12:01 PM
172.28.106.181 Gratuitous ARP Dec 29 2014 03:08 PM
172.28.106.184 Gratuitous ARP Dec 30 2014 05:25 PM
172.28.106.66 Gratuitous ARP Jan 02 2015 09:44 AM
172.28.106.194 Gratuitous ARP Jan 03 2015 03:14 PM
172.28.106.106 Gratuitous ARP Jan 07 2015 01:54 PM
172.28.106.112 Gratuitous ARP Jan 07 2015 04:32 PM
172.28.106.113 Gratuitous ARP Jan 08 2015 04:48 PM
172.28.106.103 Gratuitous ARP Jan 09 2015 12:53 PM
172.28.106.164 Gratuitous ARP Jan 13 2015 12:13 PM
172.28.106.155 Gratuitous ARP Jan 13 2015 03:54 PM
172.28.106.168 Gratuitous ARP Jan 13 2015 05:12 PM
172.28.106.169 Gratuitous ARP Jan 14 2015 05:07 PM
172.28.106.170 Gratuitous ARP Jan 14 2015 05:50 PM
172.28.106.197 Gratuitous ARP Jan 16 2015 06:18 PM
172.28.106.60 Gratuitous ARP Jan 19 2015 07:56 AM
172.28.106.88 Gratuitous ARP Jan 19 2015 05:17 PM
172.28.106.94 Gratuitous ARP Jan 20 2015 12:46 PM
172.28.106.101 Gratuitous ARP Jan 21 2015 10:15 AM
172.28.106.102 Gratuitous ARP Jan 21 2015 02:08 PM
172.28.106.147 Gratuitous ARP Jan 28 2015 11:04 AM
172.28.106.159 Gratuitous ARP Jan 28 2015 12:37 PM
172.28.106.128 Gratuitous ARP Jan 28 2015 02:27 PM
172.28.106.165 Gratuitous ARP Jan 29 2015 12:31 PM
172.28.106.166 Gratuitous ARP Jan 30 2015 07:40 AM
172.28.106.178 Gratuitous ARP Jan 30 2015 02:20 PM
172.28.106.183 Gratuitous ARP Jan 30 2015 02:39 PM
172.28.106.69 Gratuitous ARP Feb 02 2015 09:40 AM
172.28.106.76 Gratuitous ARP Feb 02 2015 07:18 PM
172.28.106.91 Gratuitous ARP Feb 02 2015 08:17 PM
172.28.106.93 Gratuitous ARP Feb 02 2015 08:20 PM
172.28.106.200 Gratuitous ARP Feb 04 2015 01:41 PM
172.28.106.96 Gratuitous ARP Feb 05 2015 09:57 AM
172.28.106.111 Gratuitous ARP Feb 05 2015 01:42 PM
172.28.106.108 Gratuitous ARP Feb 06 2015 08:04 AM
172.28.106.122 Gratuitous ARP Feb 09 2015 05:11 PM
172.28.106.174 Gratuitous ARP Feb 11 2015 06:17 PM
172.28.106.179 Gratuitous ARP Feb 12 2015 06:18 PM
172.28.106.83 Gratuitous ARP Feb 16 2015 03:56 PM

DHCP Conflict between ZfD 4 Agent and Novell Client

I am having problems with the use of Novell Client versions that support
DHCP settings tab (Tree, Context, Server).
This is in this board because my problem is only reproduced when ZENworks
for Destkops 4 (IR5 and IR7) Workstation Management component is installed.
THe problem is this:
Every now and then, logging in with the novell client displays 886f errors
in the login results window, and other strange communication errors.
If I release and renew the IP, it works fine after that.
If I reboot, there is a chance I get the same problem.
This absolutely does not happen when I have the two options for DHCP
settings in the Novell Client unchecked (Server->Binary Data).
Now, is ZfD Workstation Manager getting the Preferred Server IP from DHCP
as well during system startup? Is this clear? Happens on both Windows
2000 and Windows XP.
I have no access to the router serving DHCP so I don't know the details on
that end.

There was (is?) a conflict that is supposed to be solved,
but I'm not 100% convinced that is true. Since I always
use Client32 I remove novdhcp.dll in my ZfDAgent transform,
even now with ZDM7 because I've seen the "semaphore" error
there too if I don't.
See:
http://support.novell.com/cgi-bin/se...?/10090994.htm
http://support.novell.com/cgi-bin/se...?/10093676.htm
http://support.novell.com:80/cgi-bin...?/10091089.htm
Regards
Rolf Lidvall
Swedish Radio (Ltd)

Manual IP and DHCP conflicts

My Barricade g died (SMC2804WBRP-G). I replaced it with an Airport Extreme (802.11g).
With the Barricade g, I had manually assigned IP address to all the computers on the LAN (range 192.168.x.1-192.168.x.99). The router distributed IP addresses to the wireless clients via DHCP range (192.162.x.100-192.168.x.200)
I've setup the AEBS to Distribute IP addresses and selected Share a single IP address (using DHCP and NAT).
BUT, the AEBS is assigning some of the manual addresses to wireless client IP requests. Then the computer that is supposed to have a manual IP address doesn't have one. Basically, the manual and DHCP addresses are coming from the same pool and causing conflicts.
How do I deal with manual IP addresses AND DHCP with this router?
Thanks

David,
Thanks for the input. But, I may have misread my post.
From my original post.
'With the Barricade g, I had manually assigned IP address to all the computers on the LAN (range 192.168.x.1-192.168.x.99). The router distributed IP addresses to the wireless clients via DHCP range (192.162.x.100-192.168.x.200).'
In other words, on the network, LAN=static IPs, Wireless clients=DHCP.
You can have both static and DHCP on the same network.

Trying to resolve a DHCP conflict involving Airport Extreme

I have my LAN set up so that the router hands out addresses with DHCP in the 192.168.1 range. Also on the network is an Airport Extreme (an older 11g model running the 5.7 firmware). I am having a terrible time trying to configure it so that it hands out addresses to its clients in the 10.0.1 range. No matter what I try, the Airport DHCP server is overridden by the DHCP server on the main router and a 192.168 address is assigned.
On the first configuration page of Airport Utility under the Internet tab, I have chosen Connect using Ethernet and DHCP. And I have chosen "Share a public IP address." Under the DHCP tab I've indicated beginning and ending IP addresses from 10.0.1.10 to 10.0.1.20. Why then when I connect to the airport with, say, my laptop, do I get a 192.168 address?
Any advice would be much appreciated.

What you are trying to do is quite common, but perhaps the key is that the LAN with the DHCP router assigning 192.168.1 addresses must be connected to the AEBS via its WAN port.
In a default (configured from Factory Reset) scenario, the AEBS will request an IP address from the router via DHCP for itself, and will distribute IP addresses for its clients (wireless and via its LAN port) via DHCP from the pool you've specified if you have it set up to "Share a public IP address."
You can read more about setting up this type of network starting on page 24 of the Apple manual Designing AirPort Networks.
I suspect what's happening is the router is connected to your AirPort's LAN port, which causes a race condition between the two DHCP servers as to which will provide an address to new network devices.

WRT54G firmware Mac DHCP conflict

I updated my WRT54G version 6 to firmware version 1.01.0 and (after 2 days when things worked fine) lost the ability for any of my 3 Mac computers (intel iMac and pismo powerbook) to get an IP address either by wired connection or wireless connection to the router. My Windows laptop connected just fine by wired and wireless connections. The Macs could see the router if manually set to IP 192.168.1.50, but did not get an IP address if set to DHCP. No amount of resetting router, modem and computers helped. I reflashed 1.01.0 using the PC but that did not help. I flashed back to firmware 1.00.9 and immediately got back wired and wireless connections with all of the Macs. There are at least three other reports of people solving exactly the same problem posted in the Apple discussion boards with other Mac models.

Check this link.... ftp://ftp.linksys.com/pub/network/
Look for wrt54gv5_v6_fw_1.00.9_US_code.zip

DHCP conflicts

Hi,
I have configured a 3550 switch with 3 vlans. With the following configs
interface Vlan1
description ---> MANAGEMENT VLAN <---
ip address 192.168.10.1 255.255.255.0
ip helper-address 192.168.3.8
interface Vlan2
description ---> SERVER VLAN <---
ip address 192.168.3.10 255.255.255.0
ip helper-address 192.168.3.8
interface Vlan3
description ---> OFFICE VLAN <---
ip address 192.168.11.1 255.255.255.0
ip helper-address 192.168.3.8
For some reasons i am not getting IP address from the DHCP server even after assigning the scope.
Any one have some idea about that why??
Thanks
Rajesh

STP is enabled by default on all ports. DHCP is known to run into problems when access ports has to go through the different states of STP.
Enabling spanning-tree portfast will put the access port directly into forwarding state without having to transition through blocking, listening, learning and forwarding states.
Syntax depends on the type of switch you are using. If you are using an IOS based switch, try 'spanning-tree porfast' on the access ports.
HTH,
Sundar

Guest network DHCP conflict

I get this message and would like to know how to fix the problem. This airport wireless device rejected a DHCP address in the same subnet as its internal DHCP server for the guest network. you should change the DHCP Range for the guest network. How do I do this.
Thank you

Welcome to the discussion area, anthony!
I get this message and would like to know how to fix the problem.
Open AirPort Utility and click on Manual Setup
Click the Internet icon
Click the DHCP tab
The DHCP ranges will be displayed for your Main network (top line) and Guest network (third line). Note the range that your Main network is using, either 10.0, 172.16 or 192.168. Then select a different range for the Guest network.
So for example, if your Main network is using 10.0, then you would select either 172.16 or 192.68 for the Guest network and Update to save your changes.

Question # 2--how to avoid the DHCP conflict issue, double NAT, etc.

I'm having a tough day wasting hours working on the TC. It once worked fine for a year. Now, I'm struggling to maintain a connection at all.
I may be doing this wrong but I'm using two screens to manage this.
1. preferences/network
2. the TC internet connection settings
I had written all of my settings that worked on a piece of paper. Now that I've had to reset everything earlier today by plugging/unplugging stuff per Comcast orders, I'm wondering if all of my previous settings are worthless.
Reading possible solutions on here I tried to set the connection sharing to bridge to avoid the double NAT issue. This resulted in a message that more than one computer had the same IP address and I couldn't access the internet so I went back to sharing the public IP address like I had before.
I had, and I'm trying to have now, IPv4 configured manually. When I use settings like I had before, it tells me the DHCP range is invalid. If I increase the 3rd digit/group of numbers to change the range, it re-boots but I'm unable to get to the internet.
I don't know what I'm doing wrong. Any help?

Thanks to you both for responding. I had actually already read that Networking 3.0 document ... and since options 1-3 were not allowing the QuickVPN to work and options 4+ resulted in lost FIOS TV services I wasn't pursuing any of those options. Out of all of them it sounds like Bridging the Westell would be closest to what I want (enabling the Cisco router to acquire the public IP address). But I'm not willing to sacrifice my TV functions so even that option is a non-starter for me.
Over the past two weeks I have spent some 30 or 40 hours researching and then tinkering with the configuration on the routers (and VPN client software -- QuickVPN and shrewsoft VPN client). So I just invested about 15 minutes in downloading the free TeamViewer software. And although I didn't want to go the "3rd party software" route I'm actually glad I tried it. I now have a working VPN connection via TeamViewer, and through the VPN am able to use windows remote desktop just fine -- which was my goal all along. I'm concerned about the 3rd party software / security ... but at least this works. And I can always disable the TeamViewer Service when I'm not using the software.

One Internet Connection, Two different LANS & Two DHCP Servers, How to share internet without conflict?

I have two LANs and one internet connection. Each LAN has its own DHCP server. I want to be able to have internet access on BOTH LANs but don't
want to have a DHCP conflict between them.
The main LAN is a Time Warner Cable modem and a Cisco router running DHCP going to a 48 port switch that has all the workstations connected.
The second is a stand alone Windows 2012 WDS server which is ONLY use to image computers via WDS. The server is running DHCP as well and is connected to another 48 port switch where I connect systems that need to be imaged.
I want to be able to provide internet access on LAN with the Windows 2012 WDS server so after I image the computers I can download drivers direct from the internet. The Windows WDS server has two NIC cards but I am only using one. Is
it possible to configure this so the internet from the main LAN is shared to the WDS server and its clients without causing problems with the two DHCP servers? Here is a basic network diagram. Thanks!

Hi Adam,
To share the internet on secondary VLAN, please follow the steps below:
Connect the secondary switch to Cisco router
Configure the devices on secondary VLAN to use Cisco router as its' gateway
Configure NAT for secondary VLAN on Cisco router
Due to different manufacturer has different ways to configure, for detailed configuration information, please consult the manufacturer of the switch and router.
Best Regards.
Steven Lee Please remember to mark the replies as answers if they help and unmark them if they provide no help. If you have feedback for TechNet Support, contact [email protected]

Assigning DHCP IP address by SSID

Hello,
I want to assign IP addreses by SSID on the 861W. I have two Vlans on the router on two different subnets, and one DHCP pool for each subnet. On the AP I have two SSIDs on each of the Vlans.
However, when I associate with the different SSIDs, I get an ip address from the same DHCP pool, instead of different pools. I want ip from different subnets with different SSIDs.
Any help is greatly appreciated.
Here's the AP config:
version 12.4
no service pad
service timestamps debug datetime msec
service timestamps log datetime msec
service password-encryption
hostname ap
enable secret 5 <hash>
no aaa new-model
clock timezone EST -5
clock summer-time EDT recurring
dot11 ssid Public
vlan 1
authentication open
dot11 ssid Voices
vlan 2
authentication open
username Cisco password 7 <hash>
bridge irb
interface Dot11Radio0
no ip address
no ip route-cache
ssid Public
ssid Voices
station-role root access-point
interface Dot11Radio0.1
encapsulation dot1Q 1 native
no ip route-cache
bridge-group 1
bridge-group 1 subscriber-loop-control
bridge-group 1 block-unknown-source
no bridge-group 1 source-learning
no bridge-group 1 unicast-flooding
bridge-group 1 spanning-disabled
interface Dot11Radio0.2
encapsulation dot1Q 2
no ip route-cache
bridge-group 1
bridge-group 1 subscriber-loop-control
bridge-group 1 block-unknown-source
no bridge-group 1 source-learning
no bridge-group 1 unicast-flooding
bridge-group 1 spanning-disabled
interface GigabitEthernet0
description the embedded AP GigabitEthernet 0 is an internal interface connecting AP with the host router
no ip address
no ip route-cache
interface GigabitEthernet0.1
encapsulation dot1Q 1 native
no ip route-cache
bridge-group 1
no bridge-group 1 source-learning
bridge-group 1 spanning-disabled
interface GigabitEthernet0.2
encapsulation dot1Q 2
no ip route-cache
bridge-group 1
no bridge-group 1 source-learning
bridge-group 1 spanning-disabled
interface BVI1
ip address dhcp client-id GigabitEthernet0
no ip route-cache
ip http server
no ip http secure-server
ip http help-path http://www.cisco.com/warp/public/779/smbiz/prodconfig/help/eag
bridge 1 route ip
line con 0
no activation-character
line vty 0 4
login local
end

Thanks for the suggestion. However, when I implement these commands clients on SSID Voices (Vlan2) cannot connect to the DHCP server on the router.
Here is my config on the router:
Current configuration : 2200 bytes
! Last configuration change at 10:45:20 EDT Mon Apr 27 2009 by Thomas
! NVRAM config last updated at 15:26:52 EDT Sat Apr 25 2009 by Thomas
version 12.4
no service pad
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
hostname pa-router
boot-start-marker
boot-end-marker
logging message-counter syslog
no aaa new-model
clock timezone EST -5
clock summer-time EDT recurring
no ip source-route
no ip dhcp conflict logging
ip dhcp pool 0
network 192.168.0.0 255.255.255.0
default-router 192.168.0.1
dns-server 65.19.88.195
ip dhcp pool 1
network 192.168.1.0 255.255.255.0
default-router 192.168.1.1
dns-server 65.19.88.195
ip cef
username Thomas privilege 15 secret 5
archive
log config
hidekeys
interface FastEthernet0
no cdp enable
interface FastEthernet1
no cdp enable
interface FastEthernet2
switchport access vlan 2
no cdp enable
interface FastEthernet3
switchport access vlan 2
no cdp enable
interface FastEthernet4
ip address 65.19.88.211 255.255.255.224
ip nat outside
ip virtual-reassembly
duplex auto
speed auto
interface wlan-ap0
description Service module interface to manage the embedded AP
ip unnumbered Vlan1
arp timeout 0
interface Wlan-GigabitEthernet0
description Internal switch interface connecting to the embedded AP
interface Vlan1
ip address 192.168.0.1 255.255.255.0
ip nat inside
ip virtual-reassembly
interface Vlan2
ip address 192.168.1.1 255.255.255.0 secondary
ip address 207.136.203.109 255.255.255.252
ip nat inside
ip virtual-reassembly
ip forward-protocol nd
ip route 0.0.0.0 0.0.0.0 65.19.88.193 permanent
no ip http server
no ip http secure-server
ip nat inside source list NAT interface FastEthernet4 overload
ip access-list standard NAT
permit 192.168.0.0 0.0.0.255
permit 192.168.1.0 0.0.0.255
no cdp run
control-plane
line con 0
no modem enable
line aux 0
line 2
no activation-character
no exec
transport preferred none
transport input all
line vty 0 4
exec-timeout 120 0
privilege level 15
login local
scheduler max-task-time 5000
end

DHCP on 1841 IOS 12.4

Cannot get DHCP to work on Cisco 1841 IOS 12.4 router.
Clients send DHCP discover packets, not getting DHCP Offer packets from the router.
1. does "service dhcp" need to be expclitly listed in running config?
2. does bootp need to be enabled?
Here's my running config:
version 12.4
no service pad
service tcp-keepalives-in
service tcp-keepalives-out
service timestamps debug datetime msec localtime show-timezone
service timestamps log datetime msec localtime show-timezone
service password-encryption
service sequence-numbers
hostname xxxxxxxxx
boot-start-marker
boot-end-marker
logging message-counter syslog
logging buffered 51200 warnings
no aaa new-model
clock timezone EST -5
clock summer-time EDT recurring
no ip source-route
no ip dhcp conflict logging
ip dhcp excluded-address 192.168.103.1 192.168.103.249
ip dhcp pool DOT
   import all
   network 192.168.103.0 255.255.255.0
   domain-name xxxxxxxxx.com
   dns-server 192.168.100.2
   default-router 192.168.103.1
ip cef
no ip bootp server
no ip domain lookup
ip domain name yourdomain.com
login block-for 100 attempts 10 within 100
login delay 5
login on-failure log
login on-success log
multilink bundle-name authenticated
ip tcp synwait-time 10
interface FastEthernet0/0
description xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
ip address 192.168.103.1 255.255.255.0
ip access-group 100 in
ip helper-address 192.168.100.2
no ip redirects
no ip unreachables
no ip proxy-arp
ip accounting access-violations
ip flow ingress
speed auto
half-duplex
no cdp enable
interface FastEthernet0/1
no ip address
shutdown
duplex auto
speed auto
interface Serial0/0/0
ip address w.x.y.z 255.255.255.252
ip access-group 110 in
no ip redirects
no ip unreachables
no ip proxy-arp
ip accounting access-violations
ip flow ingress
encapsulation ppp
no peer neighbor-route
no fair-queue
no cdp enable
router bgp 65011
no synchronization
bgp log-neighbor-changes
redistribute connected
neighbor w.x.y.z remote-as 65000
neighbor w.x.y.z remote-as 65000
no auto-summary
ip forward-protocol nd
ip http server
ip http access-class 90
ip http authentication local
ip http timeout-policy idle 600 life 86400 requests 10000
access-list 90 remark HTTP Access-class list
access-list 90 permit 192.168.103.0 0.0.0.255 log
access-list 90 permit 192.168.100.0 0.0.0.255 log
access-list 90 deny   any log
access-list 100 permit tcp 192.168.103.0 0.0.0.255 any
access-list 100 permit udp 192.168.103.0 0.0.0.255 any
access-list 100 permit icmp 192.168.103.0 0.0.0.255 any
access-list 100 deny   ip any any log
access-list 101 remark VTY Access-class list
access-list 101 permit ip 192.168.100.0 0.0.0.255 any log
access-list 101 permit ip 192.168.103.0 0.0.0.255 any log
access-list 101 deny   ip any any log
access-list 110 deny   ip 10.0.0.0 0.255.255.255 any log
access-list 110 deny   ip 172.16.0.0 0.15.255.255 any log
access-list 110 deny   ip 127.0.0.0 0.255.255.255 any log
access-list 110 deny   ip 255.0.0.0 0.255.255.255 any log
access-list 110 deny   ip 224.0.0.0 31.255.255.255 any log
access-list 110 deny   ip host 0.0.0.0 any log
access-list 110 deny   ip 192.168.103.0 0.0.0.255 any log
access-list 110 deny   ip host w.x.y.z any log
access-list 110 deny   icmp any any redirect log
access-list 110 permit ip any any
snmp-server community blah RO
snmp-server community blah RO
control-plane
line con 0
exec-timeout 15 0
login local
line aux 0
exec-timeout 5 0
line vty 0 4
access-class 101 in
exec-timeout 15 0
privilege level 15
login local
transport input telnet
line vty 5 15
access-class 23 in
privilege level 15
login local
transport input telnet
scheduler allocate 4000 1000
ntp update-calendar
ntp server w.x.y.z source FastEthernet0/0
end

Hi,
ip dhcp excluded-address 192.168.103.1 192.168.103.249
What mean this command ? You want to exclude address from .1 to .249 :)
Change the exclude addresses range (e.g. 103.1 to 103.50 or somthing else), I hope it will work
Don't forget to rate helpfull posts
Sajid Ali Pathan

IOS DHCP Best Practices

Hi Group,
I have a query regarding DHCP conflicts. One of our customer is using Cisco 4500 switches in Core/Distribution and these switches are running DHCP service as well. There is one DHCP Pool configured for IP Phones (172.21.17.0/24). Yesterday we got compalint from cutomer that IP Phones are not able to get IP address so I checked the primary 4500 switch and found 'DHCP conflict' log messages so I used ' claer ip dhcp conflict *' command and after that all IP Phones started getting ip addresses.
What could be the possible cause of this problem ? Should we disable logging of DHCP conflicts ?
Can we avoid such incident by using 'ip dhcp ping' command ? Kindly guide me in this reagrd.
Thanks in Advance.
Regards,
Mujeeb

Hi Andrew,
Here is the setup of our client,
- 2*4500 are working in primary/secondary setup.
- Voice VLAN is 12 and DHCP pool for IP Phones is 172.21.17.0/24. Same DHCP pool is configured on both primary & seconadry switch.
- HSRP is running, Primary 4500 is 'Active' Router.
- Primary 4500 is root switch for VLAN 12.
- All edge switches are connected with primary and secondary 4500 except 2 switches which are cascaded with each other and one of them is only connected with secondary 4500 so root port is going towards secondary 4500. As per my understanding when IP phones which are connected with this edge switch will require IP Address from DHCP then they will broadcast the request. In the result broadcast traffic will actually flow through secondary 4500 to reach root switch but secondary switch is also running DHCP service with same DHCP pool so it will provide the IP Addresses to specific IP Phones. This setup could result in DHCP IP conflicts ??
Regards,
Mujeeb

DHCP conflict

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