Cisco WAN :: 3750 Switch - Clear IP DHCP Conflict / Binding
May 10, 2013
I configured an DHCP server on cisco 3750 switch . Wher in w3750 gets connected to plain l2 switch 2960 on floor and machine gets connected to 2960 port. [code] Below is the description of problem:
-> The Cisco 3750 switch is the DHCP server. VLAN 108 is named as internet vlan.
-> Ports in Cisco 2960 switch has been configured with "switchport access vlan 108".
-> There were no problems at all and everything had been working smoothly.
-> 3 days back, users started complaining that they couldn't access the internet. Up on troubleshooting the issue, I found out that there was an issue with the DHCP server as the computer couldn't get any IP address at all. After setting static IP address, the internet started working again.
If I bind IP to MAc address reservation on core 3750 switch for some time of moment it works but after that machine gets unreachable .I restarted the 3750 switch and also all the 2960 switches over the weekend, however, the issue still hasn't been resolved yet. I did issue the command "clear ip dhcp conflict *", clear ip dhcp binding * but no joy at all.
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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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Aug 19, 2012
We have a 3750x switch with some issues on the arp. Our servers become unreachable for some time, buy when I clear the arp cache, I am able to ping the server again. I have tried adjusting the arp timeout but I don't think doing so would be the permanent solution.
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Nov 13, 2010
I have cisco 800 router, router configure as DHCP server, i want to bind user MAC ID with IP and block only Internet Access.
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Sep 30, 2011
Can the DHCP server on an ASA be configured with static bindings like IOS routers can?
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Dec 16, 2010
I am using a 1811W and CCP for configuration. I am trying to assign client names to devices on the LAN so that when a network scanner is used, the client name is displayed. I have attached part of the running config after a binding has been done. My assumption is that the scanner should now show 192.168.1.109 as name <Supermicro>, but the name is blank. Is this configured correctly for what I am trying to acheive?
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Jan 8, 2012
I have a 1250 AP connected to an Switch Cisco 3750. We have a SSID(v lan 1 - native) which get an IP Address from our DHCP Server(located in a Windows 2003 server). I added a new SSID in VLAN 2 and I would like no to use the DHCP Server but to make the AP get an IP Address from the pool I created in the own AP (ip dhcp pool Guest) but every time I try to connect the new v lan, it doesn't get an ip address.
Follow the settings of the AP.
version 12.4
no service pad
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
[Code]...
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Nov 27, 2011
WE HAVE cISCO 2960 SWITCHES. this switch acts as a dhcp server for the hosts connected to it. Provided mac based binding to the hosts, with enabled dhcp snooping and IP source guard per interface.' I have a problem with single host couldnt get an ip from dhcp as he binded based on mac: manualip. Here is my config: We have a VLAN99, 70 hosts connected should get an ip based on mac
switch(2960<config>interface vlan99
# ip address 10.10.14.2 255.255.255.0(code)
The above host amit (10.10.14.31 swhould get this ip bindded with mac) but hez not getting manual ip i.e 10.10.14.31, but if an ip excluded from the dhcp free, he can get that ip i.e automatic ip . every other host are getting the ips as binded in the pool manual ip. Checked with
**sh mac-address table dynamic vlan 99 ()
**clear ip dhcp binding * or 10.10.14.31
** clear ip dhcp snooping binding
*** clear ip dhcp conflict *
Tried to change pool names. All these troubleshoot couldn't make me success in providing amit an manual ip.
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Mar 15, 2011
I have a Cisco 3750 running DHCP. We have a lot of guest users on the network, so the DHCP conflict table fills up quickly, and when it does, users can not get on the wireless network. I have to go in and clear the DHCP conflict log. (clear ip dhcp conflict *) and the problem is resolved. I see in the Cisco documentation if you don't have a DHCP database agent configured you should disable that log. I just want to make sure what the steps are and the ramifications are of disabling that log. Would IP address's still be freed up to use on the network? It also said about enabling 'ip dhcp ping' so DHCP will ping the address first to see if it's available.
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Jun 13, 2012
DHCP conflict on 881-W with the internal AP?I have (12) 881-W chassis in the field. They are running DHCP services to the wired users as well as to the internal AP for reachability / management / etc. The scope for the internal AP is a /30 so only one address is in the scope and it is intended for the internal AP. This serves a a point to point link between the internal AP and the internal Router inside the 881-W chassis.
Somehow the 881-W DHCP server is getting out of synch and a conflict is occurring. It seems at some point, either at boot-up or lease expiration/renewal, the DHCP server is performing a ping to verify that the address is not in use. The AP has this address assigned prior and replies to the ping causing a conflict. I noticed an AP down today, checked the 881-W uptime and the conflict correlates to the same time. I have to manually clear the conflict and everything works as it should.The existing 12 881-w's could grow to 100's over time, so the manual intervention of clearing the conflict is not going to scale. I really want to stay away from static reservations.
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Sep 14, 2010
I've configured ip dhcp snooping on several vlans I want to monitor and the binding table doesn't seem to be building.eature DHCP is on, global ip dhcp snooping is enabled, VLAN snooping is enabled on the vlan's I want to monitor and my trusted interfaces are also configured. Alas no binding entries in the table! 7K is running 4.2(6).
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May 2, 2012
I just found out that one of our 10 3750's has been assigned with an IP Address that is in conflict with a PC that has been in production long before this 3750 was deployed in our environment. Good thing it is servicing devices on a separate vlan. The conflict IP Address is assigned to the default vlan of the switch so we can connect to it from the core.If I change the IP Address of the switch, will it reboot and momentarily disconnect the devices connected to it?
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Apr 21, 2013
We have VSS configured between Cat-6509 switches (s72033-advipservicesk9-mz.151-1.SY.bin)..For the voice vlans,dhcp scope is configured within VSS and ip addresses are assigned to ip phones from these pools configured within VSS.Cat 3750 stack is connected with dual links to this vss. IP phones are connected to cat 3750 switches and desktop is connected back to IP phone. For data vlans IP addresses are assigned from external dhcp server.
Currently we are facing lot of ip conflicts for ip phones and after clearing the dhcp conflicts, IP phones starting getting IP addresses..(sufficient IP's do available in the dhcp scope for IP address assignment). (What exactly the role of no ip dhcp conflict logging command......)
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Oct 8, 2012
Im setting up SBS 2011 in a new office. From what I understand, SBS 2011 needs to be the network DHCP server for everything to run well under Active Directory. The conflict is with a FIOS router, that also �needs� to be the DHCP server in order to communicate with a set-top box (MOCA bridge.) Verizon lists a handful of network configurations with multiple routers that might work, although completely unsupported. Is it possible for router, SBS2011, and set-top box to coexist in harmony on the same network (preferably keeping DHCP server on the SBS box)?
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Mar 21, 2011
There are list of ips and corresponding mac address in ARP list and Binding setting page of the routers in our company.
I would like to know what it is meant for. This was done by our network admin. I would like to learn about it.
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Feb 7, 2012
I have switch 2960 and router that connect with one interface to that switch. the link is trunk and Router function is inter vlan routing between 4 vlan. This netwrok has only one ip address space that is 10.10.2.0/24 and work without problem. We connect cisco switch 2960 with optic link to another switch that in stack 3750 which configured as trunk link and allowed only 3 vlan between them. In the other side netwrok which consist the switch 3750 we have different subnet ip address that switch working in layer 3 too. the problem is that when I permit vlan 210 in the switch 2960 only layer 2 between this switch and the 3750 in network that consist th ip address 10.10.2.0/24 devices, if I disconnect and then connect pc to network he says that he has ip conflict and in the log he show mac address of router that has vlan 210 subinterface configured with 10.10.2./24 subnet. But how I gibe back vlan 210 from permited vlan in trunk devices start normaly working. If I again put vlan 210 to permit vlan in that trunk devices again said that there are conflict ip address and show mac address vlan 210 router subinterface.
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Feb 8, 2011
Is there any way to clear the archived DHCP list on the Belkin F5D7230-4 wireless router? Over the years there have been a lot of connections, most are no longer around but the Belkin holds on to the list. I can find no way to clear it to get it back to what is currently connected. I have tried a soft reboot, unplugging power etc but it seems like I will have to do a factory reset and apart from not being able to find my ADSL login details, I would have to reset all my settings.
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Jun 5, 2012
We have several 3750 stacks across our campus that we are unable to completely clear port security on. We have mac address stick set up on all access ports. When we clear the sticky address on the port, the mac address is removed from the running config like normal, but we keep getting port-security voilations. If port security is taken off the port completely, i.e. no switchport port-security, traffic still doesn't pass the port. Even clear port security across the stack doesn't work. If we try to reload the stack, only the master reboots, and the other switches in the stack lose switch capabilities.
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Jan 12, 2012
How to clear dhcp lease in WLC 6.0.199 from the IP leased from internal server?
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Aug 22, 2011
I have a 4500 Catalysts switched (4510 R ) that require the configuration to wiped back to factory default setting, How would i go about clearing the configuration on each module board
The chassis consists of
2 x Supervisor engines v WS-X4516 with Flash cards
4 x WS x84448 GB RJ45 48 port switches
1 x WS x4306 GB Switch Module
I also have a Catalyst 6500 that requires each module within the chassis to we wiped back to factory defaults
1 x Supervisor engine WS X 6k SUP 2- 2GE
1 x WS X6416 G-Bic 16 port GB Ethernet
4 X WS X 6148 CE-TX Base T GE 10/100/1000
1 x WS X6348 48 Port Inline Power Capable
And i have a Catalyst WS - C 6513 with the following Module card that need the configuration wiped to Factory defaults as well
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Nov 2, 2011
i have an issue to connect a trunk between cisco switch and extreme switch i have many vlans that i want to cross via a link between cisco 3750 switch and a Extreme Alpine 3800 switch
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Nov 18, 2012
I have two 3750-X configured to be a stack and I am planning to re-rack these somewhere else. What I would like to know is what are the effects of having the master switch itself lose power? Does it immediately just make the member take over master (there should be no election since there are only 2 switches??) and there would be no loss of connectivity?
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Feb 20, 2013
I'm trying to enable dhcp server on it. done this how to [URL] It works, but unfortunately the client takes almost 2 min to get an ip.
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Aug 16, 2011
I have a WCS that I use to manage 8 controllers (2 WiSM's totaling 4 controllers, and 4 more controllers at remote locations). All controllers connect to 3750 switches. The layer three interfaces for all V LAN's that are related to the wireless network are created on these switches. Each layer three interface has a helper address that points the devices in the sub net to the correct DHCP server.
When a wireless device requests a DHCP request I believe it gets to that server based on the relay from the layer three interface on the 3750. However, I know that the virtual interface on the controller is also requesting an address because my firewall is flooded with deny statements. The virtual interface is configured for 1.1.1.1 and so it gets blocked. I am starting to question the use of this interface considering the fact that it is getting blocked and the clients are still getting address.
Are both interfaces trying to act as DHCP relays? Could I setup the controllers to be the only relay (without using the virtual interface)?
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Dec 13, 2010
Can we Configure DHCP server in 3750 ? we have configure DHCP server in 1841 router but some reason we want remove router .
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Dec 4, 2011
I got a set of dhcp pool in one 3750 attached to diferent Vlans in the network, the wired network works fine, you can get from any switch port across the LAN a diferente VLANs IP. In my wlc2504 I got 5 WLANs with the DHCP server pointed to the VLAN in the 3750, but I just got one set of ip when i tried to connect to diferent WLAN, without connectivity, I can see all the Ap's, and ping the VLANs in the 3750,
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Dec 27, 2011
a power analyzer in my network is sending some packets that are unexpected and incorrectly recognized as DHCPOFFERS. As a workaround, I would like to filter those packets with my Cisco switch 3750.Suppose IP_POWER_ANALYZER is the ip address, what could be the best choice
1. deny udp any IP_POWER_ANALYZER eq bootpc
2. deny udp any IP_POWER_ANALYZER eq bootpc; deny udp IP_POWER_ANALYZER any eq bootps
3. deny udp any eq bootpc IP_POWER_ANALYZER eq bootps
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Apr 16, 2013
We are configuring ACLs for a dhcp pool on Sw3750
ip access-list extended Test
permit ip any 192.168.1.0 0.0.0.31
permit ip any host 172.16.1.1
And, here is dhcp pool:
ip dhcp excluded 192.168.1.1 192.168.1.3
ip dhcp pool Name
network 192.168.1.0 255.255.255.0
default-router 192.168.1.1
But when a PC try to obtain IP automatically, it doesn't work.
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May 13, 2012
i created the 10 V LAN in my Cisco 3750 switch.All other V LAN DHCP IP's (192.168.2.X - 192.168.10.X) will be release from the DHCP server except VLAN1 . In my 3750 switch i created DHCP pool(192.168.14.X).... and i assigned to VLAN10.... but one of the client is assigned to V LAN 2(192.168.2.X) configuration. but its getting IP from the Cisco DHCP instead of DHCP server.
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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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Jul 16, 2012
I want to clear following things regarding Cisco 3750 switch.
1. Can I configure Multiple DHCP pool on C3750?
2. Performance effect due to same?
3. Can I resrve IP addrese from DHCP pool for specific MAC address.
4. Can I Exempt IP address from DHCP pool ?
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Jul 20, 2011
I've been working with a client's integrated 3750 WLC running 4.0.179.11. I want to upgrade the code because it is old plus I am having DHCP trouble. I have a couple of questions:
1. Is it OK to upgrade to SWLC3750K9-5-2-193-0.aes ? or do I need to go through 4.2 first ?
2. Will that code upgrade the bootloader at the same time?
3. How can I make sure there is enough flash space on the WLC?
4. Are there any special considerations to plan/prepare for?
The DHCP issue is failure of associated clients to get an IP address with this message found in WLC debugging:
[Code]...
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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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