Cisco Switching/Routing :: 3750X / DHCP Server Not Handing Out Specific IPs
Apr 17, 2013
I have a DHCP server for a subnet that has only lightweight WAP's in it. The DHCP server is running on the gateway for this subnet which is a 3750X 2 switch stack running 12.2(53r)se2.I have the following configured:
ip dhcp excluded-address 10.1.10.161 10.1.10.162
ip dhcp pool DHCP-VL20
network 10.1.10.160 255.255.255.224
domain-name mydomain.net
dns-server 10.11.11.30 10.11.11.40
default-router 10.1.10.161
ease 3
The server hands out up to 18 IP addresses and no more, with 20 devices on the subnet. Scanning the subnet with a 3rd party network management system I see the following IP's never get handed out or used:
10.1.10.161 - 162 (manually excluded)
10.1.10.167 - 168
10.1.10.171 - 176
10.1.10.178
and of course 2 IP's I have manually excluded, 11 IP's in all that wont get handed out. It should only be 2 that don't get handed out. I've double and triple checked the exclusion and thats the only one. so I run a 'sh ip dhcp pool' and see this:
Pool DHCP-VL20 :
Utilization mark (high/low) : 100 / 0
Subnet size (first/next) : 0 / 0
Total addresses : 30
[code]....
[edit]I should also mention that "sh ip dhcp bind" does not show these randomly excluded IP's in use. They also do not show up in any arp table I can find.I have looked all over the config and I cant find where these extra 9 addresses are being excluded. how to free up these 9 seemingly random exclusions? Haven't issued a reload and I haven't deleted and rebuilt the DHCP server yet, production network.
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Feb 23, 2012
Haveing issue with DHCP server handing out IP addresses to client connected to VLAN5 interface.ISP Router>Firewall -(WatchGuard Drop-in mode) I have several 3750 switches and one acting as a L3 switch. The L3 is configured as follow: [code]
If I connect a laptop to int fa1/0/10 I DO NOT get an IP address from the 10.100.0.8 scope. If I connect to another interface within the VLAN 1, I get an address from the 10.100.0.0 range.
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Apr 3, 2012
Have a client wanting to hand out public ip addresses to all clients from a PFSense Firewall terminating the internet connection.
How do I allow the Cisco Switches currently in place, configured with private ip addresses in the 10.10.x.x ranges and Vlans, where the main 3550 layer 3 has defined dhcp scopes for each vlan, to relay dhcp requests from all vlans to the PFSense firewall?
I assume I would take off the currently defined dhcp scopes for the vlans and configure each vlan/switch with the ip helper address and specify the PFSense firewall and that Nat would have to be disabled onthe firewall?
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Nov 2, 2011
Had a problem with a 3750 this morning not handing out DHCP addresses. The following is a sanitized config of what the switch is using. [code] The IOS installed on the switch is c3750-ipbasek9-mz.122-55.SE1.bin. What got my attention was that the sh ip dhcp pool PC showed 180 addresses being excluded. In doing the math from the dhcp excluded addresses, only 64 should be excluded.
My next step was to remove the second dhcp excluded-address line above. Doing a clear ip dhcp binding * started letting the DHCP service hand out addresses but the sh ip dhcp pool PC stil showed 180 addresses excluded.
It finally took removing the dhcp pool and putting it back in to drop the number of excluded addresses down to a value that matches the first excluded-address line. Didnt see a dhcp bug in the bug database that would explain this.
I tried re-entering the second excluded-address line from above and saw the number of excluded addresses rise as expected. When I negated the line, the number of excluded addresses dropped back to its previous value.
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Jun 16, 2012
I have a LAN with about 200 computers (192.168.10.0/24) with a DHCP Server on Windows server 2003.The problem is that my company have acquired 100 others computers that I have connected on this network.Some computer does not get IP address from the DHCP server. When I investigated the log of the DHCP server, I realized that the DHCP server was out of addresses.
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Mar 28, 2013
I'm trying to get clients to pick up a DHCP address from my server. Physical config is as follows:
4-switch stack of 3750X-48P-S (x 2) and 3750X-24S-S (x 2). 48's are physical switch 1 & 2. Data stack is working fine. That's the Core Switch
Mix of 2960S-48TS-L and -24TS-L, 2960CG-8TC-L and 3560CG-8PC-S Access switches.
physical switch 1 in Core Switch, all ports are VLAN 4. No DHCP required - VLAN 4 is infrastructure only. All switches have:
Switch#(config)int vlan 4
Switch#(config-if)ip address 10.0.4.x 255.255.252.0 (Core switch is 10.0.4.10)
Switch#ip default-gateway 10.0.4.10
Physical switch 2 in Core Switch, all ports are VLAN 8 (client access, main corporate office site)
Physical switch 3&4 in Core Switch, all ports (SFP) are trunk
[Code] .....
So in that slightly spooky, obscure way that they have, the clients ought to be picking up a DHCP address from the relevant VLAN, depending on which VLAN the access port they're connected to is in. But they don't pick up anything. Connectivity is there - everything can ping everything, including clients if I set static IPs, and including DHCP server.
Should ip helper-addresses be set on the access switch VLAN interfaces too? Or have I missed something else obvious/critical? I need to have this out and on the ground and tested within 3 weeks - this is the first hurdle and I've fallen over. Like I said at the beginning, this config (or the equivalent) works fine on Packet Tracer for distributing IP addresses.
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Oct 23, 2011
is it possible to shutdown a specific port on my 3750x and monitor this port at the same time .for example , im dealing with a mac authenticated network using port security , i want to shut down all the ports that are not used at the moment , however , if some one gets connected to the one of the shutdown ports i want to know the mac address of the user or atleast to know that i have someone who is just plugged in to the one of the shutdowned ports .
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Nov 8, 2011
I am looking for a way to bind between a switch interface (cat 3750X) and a DHCP server reply.The switch can operate as the DHCP server .a PC connected to interface Gi 1/0/1 will lways get IP address 10.0.0.1 because it is connected to interface Gi 1/0/1, a PC connected to interface Gi 1/0/5 will lways get IP address 10.0.0.5 because it is connected to interface Gi 1/0/5 and so on... (no matter the source MAC address who sends the DHCP request).
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Sep 2, 2012
Using a Cisco 1800 series router (1802) with IOS 15.1(4)M2.I am quite sure the following should somehow be possible in IOS, but I can't figure out how to do it ... :I have the situation that I need to bind specific devices by DHCP to the same IP range.
These devices (medical equipment, used in hospital) are all from the same vendor.So the first three octets in the MAC address (Organizationally Unique Identifier , OUI) are the same for each device. The next three are always 'unknown'.I know how to bind a fully known MAC address to a host ip or ip range , but is it somehow possible to do this by the OUI ?Like using some wildcard option.
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Jul 23, 2012
I imagine this question has been posted a million times before but here goes. I am trying to image a number of machines via Ghost Cast server across a 3750X stack running multiple V LAN's. I am running the IP BASE image so am aware that multicast functionality is limited.
I am running 12.2(55)SE3. I have tried adding both V LAN's into an IGMP group using the "ip igmp join-group" command which shows both V LANs as part of the group but to no real effect. To be honest though I am clutching at straws! I'm just starting to read through the documentation so hopefully that will work.
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Jan 10, 2013
We have a 3750 running IOS ver 12.2 (44) SE, it has performed great and we have never had a problem with it. However we have noticed that when we had an outage some of our Wireless APs didn't come up as they get DHCP from the 3750. The DHCP scope said IP was depleted although there were IPs to give. We had to delete and recreate the DHCP Pool. However two days later we got the same problem and then had to do the same thing over again.
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Feb 5, 2012
Basically I have netflow which i'm trying to use to export to a netflow collector. I'm pretty sure that the 3750-X does support netflow. I've recently updated IOS on the 3750-X to support flexi netflow.For some reason the netflow packets are not being exported to the server. I'm using Opmanager which should present the netflow stats in the form of a graph. I'm using a universal IOS image. (C3750E-UNIVERSALK9-M), Version 12.2(58)SE2 3750-X WS-C3750X-24T-S
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May 21, 2012
I've created a tonne of dhcp scopes on my routers before never had any issues, however this one will not hand out any addresses at all, i even give the router a reload to see if any magic happened but nothing, ive ended having to put a temp server in with just dhcp installed until i get the router diong what it should my config below, its something simple i havent seen, as ive compared it to plenty of my working DHCP configs and seen nothing.
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Dec 22, 2011
I have a Belkin model F9K1102 router supplying WAN/LAN connection to three PCs and 2 laptops. Two of the PCs are hardwired with the remainder PC and laptops are wireless. I'm using the default router IP of 192.168.2.1 and my ISP is Charter Cable (if that's of significance). The router is picking up all the dynamic IP information from my ISP and internal DHCP is enabled. Here's the issue though - when I connect a PC, laptop or iTouch (wired or wireless) with obtain IP settings automatically enabled the IP address it receives an IP address on a different subnet ie, 192.168.3.x and thus won't have WAN/LAN connection. I have tried to set the router IP to 192.168.3.1 and set the scope in the .3 subnet but the IP obtained by the device is .4! This makes no sense to me at all. The router is on the latest firmware (according to Belkin) and there doesn't seem to be any other update I can find. I have also tried another Belkin router (older model: F5D8236) and it does the same thing.
I'm not sure if this is related but I upgraded my service with Charter to a 18MB connection and a D3.0 Ubee cable modem - this issue seem to have began after this upgrade but I don't see how that would have any bearing on what is happening on my LAN IP scope and Charter tech support is pretty useless. My workaround is that I've static assigned an IP for each device in the same subnet as the router but it would be nice for the DHCP to function correctly.
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Oct 22, 2012
We currently have around 150 2975 switches and have had problems with it them not handing out PoE power to the cisco phones and access points at random times. There is plenty of power left for the switch to use. We have at least 15 that will be running fine for about a week and then all of the devices that use PoE power will shut off and will not come back on until we reload the switch. If you console in there aren't any messages that pop up and if you look at the port it just shows on connected or will show IeeePD in the power inline. We have contacted Cisco TAC and they just RMA them.
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Jun 12, 2013
I've a Cisco 1941W router which is DHCP server for data-VLANs and uses ip-helper for voice-VLANs. [code] I don't know why I can't have IP from wireless voice VLAN whereas it is OK and wired voice VLAN and conf is the same!
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Jul 9, 2012
Is it possible to configure an 881 router to act as a DHCP server to 4 VLAN's each with a different scopes all through a single ethernet interface?
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May 28, 2013
I have customer who has as Core Switch one Cisco Catalyst 3750 with the IOS c3750-ipbase-mz.122-35.SE5.I know that this image support DHCP Server configuration, but I like to implementate new vlans (approx 15) and I want to know if this switch support 15 DHCP Servers.
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Feb 2, 2013
I used to use a CentOS self-made server for intranet for my little office, but I bouth few days ago a Cisco 861 router to replace the linux box.
1. I have 2 public IP classes from my ISP. 1 class is limitted to 80mbit upload, the other to 30mbit upload. So I need some sort of DNAT to be able to know exactly which intranet computer uses big internet and which one limitted internet.
2. I need DHCP server and with static IP addresses (one computer must always have the same IP address, etc).. i have my needs for this.
3. Also I need external access to some servers inside (web, ftp, etc) [code]
So far so good, all looks simple and I can achieve this in 2 hours on a centos linux box (correct routes, ip forwarding enabled and few iptables rules for NAT/SNAT/DNAT).
But on this brand new Centos router well, i'm not even successful in pinging the outside world, nor the inside world I'm tired of reading the forums, the documentation..i want (at first) a simple scenario: vlan+dhcp, fa4 with 1 public ip address and ACCESS to the real world. I wasn't able to achieve not even that much. [code]
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May 2, 2012
i'm interested if it's possible to set the NTP server via DHCP on an 2901 Router with 15.2(2) image.
i configured the interface gigabit 0/0 as dhcp client. The DHCP Server sends to me DNS, Default GW and NTP. All is working fine, but the NTP will not be configured. i tried to add an DHCP option request, but there is no NTP (42) value. [code]
is there any way to add the value NTP (42) for the DHCP request or isnt it possible?
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Mar 27, 2012
I have trouble with a Cisco 892 Router from my Internet service provider.
Last week we switched from a virtual Router to a hardware Router. But after plugging it in our LAN Switch, the Windows DHCP Server stopped leasing IP's. I got many BAD_ADDRESS with MAC like e1:80:10:ac, e2:80:10:ac, e3:80:10:ac, e4:80:10:ac, e5:80:10:ac, ea:80:10:ac, eb:80:10:ac, ec:80:10:ac and so on.
I do not have access to the Router config, so I can not dump the config to you. We have a flat LAN, single SUB-Net(172.16.0.0/16) and no VLAN, no Spanning Tree. A Keep it Simple, Stupid(KISS) System.
A tech guy from service provider, is telling us, the error is not there fault and my switch is not correctly configured. But this is ********. For years we had a another Cisco Router from the precursor ISP and for 2 years the virtual Router from our current ISP. No trouble with my DHCP. But after plugging the new Router in, my DHCP stopped working.On the 892 is no running DHCP, but something interferences with my Windows Server 2008 R2 SP1 DHCP Server.
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Nov 14, 2011
it's possible to let the Nexus 5548UP act as a DHCP server? (or if it will be possible in future releases)
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Dec 11, 2012
I am running into a DHCP problem on a Cisco 891 running 15.0(1)M2. I am running DHCP on the router and want to reserve an address for a printer. I have done this hundreds of times on hundreds of routers. Per Cisco recommendation, I let the printer lease an address to see whether it uses it's "hardware-address" or "client-id". This printer uses the "hardware-address" format. The printer has leased 10.0.0.102 right off the bat. I want it at 10.0.0.50.
I have a DHCP pool, like this:
ip dhcp pool CLIENT
network 10.0.0.0 255.255.255.0
domain-name chsinc.ds
default-router 10.0.0.1
dns-server 10.0.0.1
lease 2
I create a "reservation" like so:
ip dhcp pool HP_LaserJet_Printer
host 10.0.0.50 255.255.255.0
hardware abcd.ef12.3456
Now I do a "show running-config" to see what I've put in and it looks just like above. Now we reset the network settings or change any network setting on the printer to force it to renew it's lease. What should happen and what usually happens is that the printer should request an IP, be offered 10.0.0.50, accept that IP and come up on that IP address. What is happening with this particular printer is that the printer requests a specific IP (the same IP that it had initially = 10.0.0.102), the router says OK and does not enforce the reservation. Then the router actually deletes the hardware-address config line right out of the running config. A "show running-config" shows that the reservation config now looks like this:
ip dhcp pool HP_LaserJet_Printer
host 10.0.0.50 255.255.255.0
See the logs below. Notice the ones in bold.
000226: Dec 12 17:34:01.382: DHCPD: Seeing if there is an internally specified pool class:
000227: Dec 12 17:34:01.382: DHCPD: htype 1 chaddr 101f.74b0.575c
000228: Dec 12 17:34:01.382: DHCPD: remote id 020a00000ae1e10100000001
000229: Dec 12 17:34:01.382: DHCPD: circuit id 00000000
[code]....
Is there a way to make the router enforce the reservation and not let clients just bring their own IP and actually make changes to the running-config of the router?
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Jan 24, 2013
I seem to be having a problem with DNS name resolution after configuring my router (Cisco 3725 running IOS image: c3725-adventerprisek9-mz.124-25.bin) for handling DHCP requests.
Before I made the change, everything was working correctly; I could ping Google.com from a computer inside my LAN and would get response from one of Google's public IP's like normal.
I had a separate DHCP/DNS server running Windows Server 2008 handling the DHCP request and DNS queries.
When I made the change, I turned off the DHCP/DNS server and issued the following DHCP commands to my router:
Code...
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Jun 5, 2013
I receive a question from a future customer about this future if its supported on " WS-C2960S-24PS-L":configuring 2 dhcp server on this swith ( 1 dhcp for voice vlan , and 1 for Data Vlan).I did some search , but i didnt find the answer .i have to advice a customer before ordering the switch.
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Apr 24, 2011
On a 4500 switch port , defined as access vlan 10, if the user connects his own dhcp server ( instead of the normal pc that should be connected ), will it cause issues with my existing network. the existing network is all static ip. In above case, will the dhcp server start looking out and assign dhcp ip's , if a user unknowingly removes his static ip and changes to obtain ip via dhcp option on the lan properties.
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Apr 26, 2012
I'm attempting to configure a Catalyst 3560-X Switch to act as a DHCP Server. There is documentation that supports this feature. Below is my config procedure however after the completed procedue no IPs are handed out to clients. [code]
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Oct 26, 2011
Can I configure a DHCP Servero on the Nexus 7018?
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Feb 10, 2013
I need to buy a cheap Cisco switch with DHCP server.Can you confirm that 2960-24-S, 2960-24TC-S and 2960-48TC-S be a DHCP server?
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May 4, 2012
I am wondering if it has its own DHCP router and if theres a command to enable it?Also Random side question. it hands out ip addresses to other devices (the 2950 im using infront of a router) but when I hook up another switch to this switch it doesnt initialize the port or try to connect? why.
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Dec 24, 2011
On a 4500 switch port , defined as access vlan 10, if the user connects his own dhcp server ( instead of the normal pc that should be connected ), will it cause issues with my existing network. the existing network is all static ip. In above case, will the dhcp server start looking out and assign dhcp ip's , if a user unknowingly removes his static ip and changes to obtain ip via dhcp option on the lan properties.
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Oct 7, 2012
I just trying to setup a dhcp server in my catalyst 3560 switch for a nortel ip phones. I show you mmy configuration:
VOICE VLAN: 3
DATA VLAN: 1
S1:10.2.110.200
port:4100
Nortel IP Phones: IP 2002 (Firmware Version 0604D9H) & IP 1110 (Firmware Version 0623C7)
Switch Configuration:
aaa new-model!aaa session-id commonip subnet-zeroip routing!ip dhcp pool datos network 10.2.100.0 255.255.255.0 default-router 10.2.100.1 lease 0 2!ip dhcp pool voice network 10.2.110.0 255.255.255.0 default-router 10.2.110.200 option 191 ascii "VLAN-A:3" option 128 ascii "Nortel-i2004-A,10.2.100.200:4100,1,5." lease 0 2!!!!no file verify autospanning-tree mode pvstspanning-tree extend system-id!vlan internal allocation policy
[Code]...
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Dec 11, 2012
a new LAN installation, two VSS pair 6509 core, 15 closets, with 3750 stacks. Floor 15 only, devices/hosts can ping teh DHCP server but cannot aquire IP addresses. no such problem on other floors?
portfast an dother parameters are intact.
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