Cisco Switching/Routing :: Ce 500 Cannot Get Ip Address From Dhcp

Aug 10, 2011

I disconnected and reconnected the powercable while holding on to the setup button until system, alert, setup go amber. The system led light began blinking green. I waited until one of the leds lights on the ports starts blinking green I then connected the ethernet cable connected to my pc.  I made sure my lan connection on my computer was set to dhcp.In the docs claim it should take about 1 minute to grab a new ip address.  After a few minutes i check the ipconfig on my pc and I get the apipa address.The setup light on the switch remains green while system is amber.  The led for port 1 stopped blinking and remains green.My pc is not grabbing an ip address I don't know what else to do.

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Cisco Switching/Routing :: 3560G - IOS DHCP AP Loosing IP Address

Nov 13, 2012

Not sure if this is a problem with the switch or the wireless AP connected to the switch, but I have a couple of 3560's, one is a 3560G and the other is a 3560, both have phones and wireless ap's connected to them.  The ap's on both of these switches continue to loose there ip address and thus disconnect from the controller.  This happens about once a week, but the odd thing is that the phones never loose there ip address.  All of my other 3560s and 3560g's that have AP's and phones connected are working fine.

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Cisco Switching/Routing :: IP Address DHCP Command Not Available On C3550

Nov 19, 2011

I'm trying to configure my C3550 with fast ethernet port 0/48 assigned to vlan 2 in static access mode and SVI vlan 2 configured as dhcp client.
 
But I see command ip address dhcp is not available on interface vlan 2:
 
Cat3550(config-if)#ip ad
Cat3550(config-if)#ip address ?
A.B.C.D  IP address 
Cat3550(config-if)#ip address  
 
Could it be a problem related to the version running on the equipment (see below the output of sh version command not sure of what EA1 stands for)? I read here [URL] that this command was introduced in version 12.1(2)T
 
If it is a version problem is there any possibility to download upgraded version for free? 
 
Cat3550>sh ve
Cisco Internetwork Operating System Software
IOS (tm) C3550 Software (C3550-I5Q3L2-M), Version 12.1(20)EA1, RELEASE

[Code].....

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Cisco Switching/Routing :: 120 IP Address From Incorrect Scope Is Assigned From DHCP

Jul 8, 2012

I am trying to setup VLANs and most of configurations are working ok now except IP address assignment from DHCP. If any computer in VLAN 120 or 130 configured with manual IP address, then all works fine. It can reach internal servers and the internet without problem.If the IP address is assigned automatically then any computer in VLAN 120 or 130 are obtaining  IP address (strangely!) from VLAN 100. Because switch ports that connected to the computer belongs to VLAN 120 or 130, the computer cannot reach internal servers and the internet with ip address from VLAN 100 . All SVI interfaces for VLAN 100, 120 and 130 have ip helper-address option defined pointing to the DHCP server. No DHCP snooping enabled on all switches at this point. DHCP server have three scopes for the three different VLANs.

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Cisco Switching/Routing :: Assigning IP Address Through DHCP On New 4500E Install?

Nov 20, 2011

The DHCP/DNS server is on ip address 10.1.100.103 with an alt on .102 I'm attempting to integrate a 4510R+E into an existing network and use existing DHCP/DNS windows 2008 server to push out IP addresses to connected computers.
 
I want to assign a VLAN to every port for management purposes and then I put an IP helper address on every VLAN.
 
I've attached a the 4500E partial config.  I'm attempting to get Gi1/44 to a state where I can plug a computer into it an resolve an ip address and gain internet access like all the devices on the existing network can do.
 
I've created a new scope in DHCP with the ip subnet of 10.60.211.0 255.255.255.0 It leases addresses from .1 to .253
 
The computer will not resolve ip addresses with this config.

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Cisco Switching/Routing :: 3560 - Dhcp - Excluded Address Range

Apr 29, 2012

we have a 3560 switch configured with EIGRP with dhcp.  We have a user that we cannot ping, however the interface show up / up and no errors on interface. the ip address is 10.2.0.199 - however we have dhcp configured to exclude the range from dhcp ip dhcp excluded-address 10.22.0.1 10.22.0.200 how can this work station get a dhcp address if we have that ip range excluded from the dhcp pool?
 
The user is off a different switch that is a uplink to this distribution switch. Traceroutes shows that the problem is with the distribution switch.

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Cisco Switching/Routing :: 3750 - DHCP Server Doesn't Provide IP Address

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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Cisco Switching/Routing :: 3911 Router DHCP Server Not Giving IP Address

Jan 30, 2011

I have a 3911 router with a 1242 AP. The problem that I have is that when the user is trying to connect, the user get the OS Ip address 169.254.168.154 and I see that when I do the "show dot11 association" command, but when I do sh ip dhcp binding on the  router I see
 
172.19.9.141        0100.18de.74db.14       Jan 31 2011 11:14 AM    Automatic
 
The router is seeing as if the router gave the ip address to the user, but the reality the user was assigne the OS ip address 169. I did "debug ip dhcp server events" and I got the following:
 
Jan 31 11:09:06.752 EST: DHCPD: Seeing if there is an internally specified pool class:Jan 31 11:09:06.756 EST:   DHCPD: htype 1 chaddr 0100.18de.74db.14
Jan 31 11:09:06.756 EST:   DHCPD: remote id 020a00000a58218400000000Jan 31

[Code].....

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Cisco Switching/Routing :: Nexus 7010 New Users Were Not Getting Ip Address From Dhcp Server

Jun 8, 2013

We  have 2 nexus 7010 switches configured with HSRP in the network. For all  the vlans core1 is Master and Core2 is standby. In the current setup we  have external dhcp server and dhcp relay is configured for all the  vlans on Master and standby switch. The setup is running the IOS 5.2
 
Activity Done: During  the Maintainacne activity, we isolated core1 switch in the network by  disabling the vpc/keepalive and all the uplinks from access switch. The  core2 switch was master for all the vlans.
 
Issue observed: It  has been observed that new users were not getting ip address from the  dhcp server. The ethereal capture showed that dhcp server was not  getting the dhcp requests from the core2 switch. We disabled the dhcp  feature in core2 and enabled again with dhcp relay again configured on  vlan interfaces .even after doing this no change was observed in  behaviour. Finally we got core1 back in network by enabling all the  links.
 
Observation: The  moment VPC link came up between the core switches, users started  getting ip's from dhcp. Then we started enabling all the uplinks on  core1.Core1 again become master for all the vlans and users continued  getting ip’s. Network running fine.
 
Further Testing

1. For  one of the vlan, core 2 switch has been made primary and for new users  checked the dhcp functionality and it was working fine. The aim was to  identify if anything wrong on core 2 related to dhcp relay

2.Again  we changed the priority for this vlan and made core1 master for the  same. This time we disabled this vlan on core1 and tried new user with  core 2 became master and dhcp functionality worked fine for new user.  Actually in this case we have simulated the same behaviour when we  observed the issue with only difference of VPC was not available during  the issue time as core 1 was isolated form network 
Inputs needed.

Is  there any known behaviour for dhcp functionality when VPC is  unavailable? If we see the test scenario2 (wherein core1 was master for  the vlan and we disable this vlan on core 1 and core 2 was able to relay  dhcp requests for new users in this vlan.) it was actually same as  scenario we observed during issue time..

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Cisco Switching/Routing :: DHCP Request Not Being Forwarded By Helper Address Same VRF 6500?

Feb 22, 2013

Version 12.2(33)SXI
 int vlan 1
description client vlan
ip vrf forwarding A
ip address 10.1.1.1 255.255.255.0
standby 129 ip 10.1.1.2
standby 129 timers 1 4
standby 129 priority 105
standby 129 preempt
ip helper-address 10.1.2.20

[code]....
 
dhcp requests are not making it to the dhcp server SAME VRF (ip helper-addres is not doing anything.....)extended vrf traceroutes on udp 67 sourced from vlan2 are fine
 
I am expecting udp unicast packets on port 67 "giaddr" relay packets on the DHCP server generated and sourced by the relay on Vlan1
 
eg. Mar  1 01:59:06.731: DHCPD: setting giaddr to 10.1.1.1
 
This exact setup works in our preprod environment with the same code.Only difference is we run Distributed etherchannel on the 6500's where this doesnt work.
 
Wireshark on the client I can see the requests being sent Going to check it with debug ip dhcp server to check the relay logs out of production hours.
 
I have seen so many people say it IS and ISN'T supported on this version of the code.e.g. [URL]
 
I am aware the helper-adddress should inherit the vrf of the interface ip helper-address vrf command is not supported.The fact it works in the PP environment.... could this be due to the Distributed EtherChanel difference? or just some bug....

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Cisco Switching/Routing :: Catalyst 2960S - Dynamically Assign IP Address To Computers Via DHCP

Aug 30, 2012

I am administering a Catalyst 2960S switch and I would like to connect several computers to it.  Some of those each have a static IP address.  For a few of them, I would like the switch to dynamically assign an IP address to them via DHCP.  Is the switch capable of doing this?  If so, how can I do it? I tried looking through Cisco Network Assistant and I couldn't find it.  Some web pages have suggested I telnet into the switch and issue commands like "ip dhcp ?" to see what commands are possible.  I can telnet in and if I type  but I get an "Unrecognized command" for both "ip ?" and "ip dhcp ?".  This makes me think I'm reading the wrong web pages. I did come across the term "DHCP snooping".  It seems relevant, but very difficult for me to grasp. 

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Cisco Switching/Routing :: Can Layer 2 2950 Switch Be Used As DHCP Server With Its Own Address Pool

Mar 18, 2009

Can a layer 2 cisco 2950 switch be used as a dhcp server with it's own address pool.

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Cisco Switching/Routing :: 2960 - DHCP Server Port-Based Address Allocation

Nov 15, 2012

Does the 2960 switches with LAN-Lite support DHCP Server Port-Based Address Allocation?

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Cisco Switching/Routing :: 4500 / 3560 - DHCP Redundancy - IP Helper Address Point To HSRP?

Jan 5, 2012

My actual Scenario
 
1 x 4500 and 1 x 3560?They are gateways of 8 Vlans?They are doing HSRP in each of those Vlans?The 4500 is the Active?There is a DHCP Pool for each of those Vlans on both gateways using "ip dhcp excluded-address" I ensured that the range of provided ips by each DHCP server will not be overlapped Obs.: Reducing the lease time, I ended with the calls bringing related problems.
 
OK, every thing is blue, every thing is fine.But the network diagram is realy complex(41 switchs, 89 uplinks), and depending of how is the network flow, one or other server answer first or latter.
 
For many reasons I would like that the secondary DHCP server would answer only if the primary DHCP server goes down.To me, the bigger reason is that DHCP database would be only in one DHCP server.But there is other reasons.
 
I passed by many frustrated solutions:Try to force a delay on the answer on one of the servers. - Impossible.Try to disable DHCP server, and, using EEM, enable it only if router became active in HSRP. - I couldn't do It.
 
What I'm thinking now is use the HSRP resource to resolve it.On both routers I would put a "ip helper-address" pointing to an Virtual_HSRP_IP.And depending on which router is the active, him will answer the request.
 
My first doubt is:Would it work?The second doubt is:Could I use the same Virtual_HSRP_IP that exists on that Vlan(see example 1),or I would need to point it to a Virtual_HSRP_IP in a different Vlan(see example 2)?

Example 1
        -----------------------------------
        |              4500               |
        -----------------------------------
        interface Vlan1
         ip address 10.10.0.2 255.255.0.0
         ip helper-address 10.10.0.1
         standby 1 ip 10.10.0.1

[code]....

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Cisco Switching/Routing :: 4506-E Excluded Dhcp Address Are Showing More Than Excluded

Nov 8, 2012

I have a Cisco Catalyst 4506-E Swtich,I configure it as a DHCP and gw for the Wireless Cisco AP through the WLC 5508,the DHCP pool reached the maximum limit I run the Show ip dhcp pool (pool name) it's show the below result
 
GIR906.PCIRQ.DC.CR.1#show ip dhcp pool 406

Pool 406 :
Utilization mark (high/low)    : 100 / 0
Subnet size (first/next)       : 0 / 0
Total addresses                : 126
Leased addresses               : 76
[Code]....

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Cisco Switching/Routing :: 2921MS DHCP NACK With DHCP Relay?

Nov 11, 2012

I have some DHCP trouble since I subnetted my network with a 2921. My clinets are in 172.16.2.0/23 and DHCP servers are in 172.16.5.0/24.Sometimes, randomly I guess, I get NACK from my DHCP server, and if I look into DHCP logs I got something like this:
 
15,11/09/12,09:52:27,NACK,172.16.3.172,switchE51D12.host.com,A0CF5BE51D12,,0,6,,,,,,,,
15,11/09/12,09:52:28,NACK,172.16.3.172,switchE51D12.host.com,A0CF5BE51D12,,0,6,,,,,,,,
15,11/09/12,09:52:29,NACK,172.16.3.172,switchE51D12.host.com,A0CF5BE51D12,,0,6,,,,,,,,

[code]....

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Cisco Switching/Routing :: 3550 / 2950 DHCP Relay Option To Router Handing Out DHCP

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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Cisco Switching/Routing :: DHCP For PC At G0/1 From G0/0 For 1941

Mar 12, 2013

I have this Cisco 1941 router with two Ethernet ports g0/0 and g0/1. The g0/0 is connected to office LAN with internet access. As my office LAN is DHCP, it will assigned a IP address for g0/0 since this g0/0 is configured as "ip address dhcp". Now my question is that i have a group of 5 pcs, namely PC1, PC2, PC3, PC4 and PC5 that is connected to the switch and one of the ports of this switch is connected to g0/1 of Cisco 1941. Is it possible that let say PC2 and PC3 (both DHCP enabled) could access the internet access from g0/0 and at the same time, the office LAN assigned IP address for PC2 and PC3 automatically?
 
                                                       Office Lan with internet access (DHCP) (Default gateway 10.0.0.1)                                      
                                                                                          |
                                                                                          |
                                                        g0/0 (DHCP enable) (DHCP assigned IP address 10.0.0.138)
                                                                                 Cisco router 1941
                                                                                       g0/1
                                                                                           |
                                                                                           |
                                                                                  HP Switch
                                                                                           |
                                                                          PC1 PC2 PC3 PC4 PC5
                                      
Is this operation possible? if possible, how to configure inside the router 1941 to achieve this objective?

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Cisco Switching/Routing :: 6509 - NAT / DHCP

Nov 30, 2011

We are looking to avoid the need to install an additional device in our network as our core 6509s are not being pushed by any stretch.  However, we are having an issue getting the 6509 to assign DHCP addresses and perform NAT.
 
Most interfaces and V LAN's on the 6509 are using public IPs and have BGP routing at the edge.  We have a trunk up link coming into the 6509 on a ws-6816 card via a SMF GBIC in slot 9, port 2 that feeds a wifi link where we are looking to provide guest access to our network.
 
We created 2 V LAN s on the switch 20 and 21.  We assigned a private IP and network to the VLAN20 interface and assigned a new public /30 sub net ip to the V LAN 21 interface.  The following configuration was applied which I thought was the required configuration based on how we would typically configure ISR routers for the same services...
 
ip dhcp excluded-address 10.200.200.1
!
ip dhcp pool WiFi_Pool
network 10.200.200.0 255.255.255.0
default-router 10.200.200.1
dns-server 4.2.2.1 4.2.2.2
[ code]...
  
What am I missing in this configuration? Note that if I create an access switch port for v LAN 20 on the switch and plug a laptop in directly to the 6509, the laptop is unable to receive a DHCP address.  If I assign the laptop an address in the 10.200.200.0 /24 range manually, I can ping 10.200.200.1 from the laptop, however, the laptop will not get to the internet as it appears to be failing to perform nat.

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Cisco Switching/Routing :: 819 Router - NAT With DHCP

May 12, 2013

I am a newbie to Cisco. I am trying to setup NAT with DHCP in our office on CISCO 819 router. I am having a problem with DHCP not assigning an IP on vlan1. I cannot figure out what i'm doing wrong. Below is my config and  debug from DHCP.
 
router#sh config
Using 4328 out of 262136 bytes
!
! Last configuration change at 05:56:39 UTC Mon May 13 2013 by cisco
! NVRAM config last updated at 05:57:16 UTC Mon May 13 2013 by cisco
[Code]....

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Cisco Switching/Routing :: 6500 DHCP Not Giving IPs

Jan 15, 2013

I have this message "DHCP Timeout"on few cisco IP Phones .try to assign IP manually and it's working fine.. seems DHCP not giving IP's to those.. 6500 have configured as DHCP pool.

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Cisco Switching/Routing :: N7Ks / DHCP Relay On NX-OS?

Nov 30, 2011

I am trying to get an understanding of some behaviour I am seeing on my N7Ks regarding DHCP relay.I have two identically configured Vlans interfaces both configured with the same two dhcp relay servers in the same order. The only difference between the two vlans is that one is HSRP active on the A side switch and the other is active on B side switch. All clients in Vlan136 (active on B side) are getting DHCP leases from the first of the two dhcp relay servers configured while all clients on Vlan 137 (active on A side) are getting DHCP leases from the second of the two dhcp relay servers. I would expect that all clients on both vlans would get leases from the first relay server configured unless that device was unavailable.

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Cisco Switching/Routing :: ME 3400 - DHCP Snooping

Sep 27, 2012

I have a problem at a place where 5 ME3400 switches are connected in a straight line. I can't do much about the topology of that place, but the problem is they are all DHCP Snooping, but uni cast replies from the dhcp server further up the hierarchy gets eaten by the first switch! I can't really see why it not only inspects in and whines about it not being for itself - it then drops the message.
 
What have we done wrong (apart from the actual layout of that place, which I can't really change)?
 
Sep 28 13:49:29: DHCP_SNOOPING: received new DHCP packet from input interface (GigabitEthernet0/1)
Sep 28 13:49:29: DHCP_SNOOPING: process new DHCP packet, message type: DHCPOFFER, input interface: Gi0/1, MAC da: 7444.012d.debd, MAC sa: 0013.1a4a.65c7, IP da: XX.YY.186.7, IP sa: XX.YY.186.1, DHCP ciaddr: 0.0.0.0, DHCP yiaddr: XX.YY.186.7, DHCP siaddr: 0.0.0.0, DHCP giaddr: 0.0.0.0, DHCP chaddr: 7444.012d.debd
Sep 28 13:49:29: DHCP_SNOOPING: binary dump of option 82, length: 20 data:
[Code] ......
 
It really should just send it on, as with any uni cast not on the switch itself - it should go out Gi0/2 really. Why isn't it?
 
[core] -- [sw1] -- [sw2] -- [sw3] -- [sw4] -- [sw5]
 
All the trunks are trusted, DAI is on (I've tried shutting it off, as well), port-security is used but it's actually not dying on the switch having the client computer, but the first one in the chain with dhcp snooping. 

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Cisco Switching/Routing :: 1841 DNS Updates From DHCP

Jan 19, 2013

I have an 1841 running Advanced Enterprise Services 12.4(22)T3 that is functioning as a DHCP server and DNS server.  What I am trying to figure out how to do is have the DNS service respond to queries about the clients of the dhcp service.  I have successfully enabled it as a caching server for other requests, like "google.com" and "cisco.com", but what about the hosts on the local LAN?
 
As an example, let's say a Windows computer connects to the network with the hostname "computer" and receives an IP address from the 1841 with the domain name "test.net".  I would like the 1841 to serve DNS queries for "computer.test.net" with the IP address that it assigned. 

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Cisco Switching/Routing :: PXE Failing With DHCP On 4506?

Jun 11, 2012

We are attempting to PXE boot from clients obtaining their DHCP lease information from DHCP pools configured on our 4506.  The PXE server, and the client are configured in separate VLANs.  We have configured option 66 to point to the PXE server IP address, and the bootfile option to point to the PXE boot configuration filename.  On the client side SVI, we also have configured the ip helper-address command to point to the PXE server (which also acts as another DHCP server for redundancy).
 
The PXE boot continuously fails stating it is unable to find the configuration file.  If we remove the DHCP pool from the 4506, and allow the client to receive their DHCP lease info from the secondary server (Windows 2k8 - same server as PXE server), they PXE boot with no issues.
 
We have no problem obtaining DHCP info, just completion of the PXE process.

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Cisco Switching/Routing :: DHCP Relay On 3560

Apr 12, 2012

Would like to impliment VLAN's on Cisco IOS Software, C3560 Software (C3560-IPSERVICES-M), Version 12.2(25)SEB4...But I need a DHCP Realy to my Windows Based DHCP Server.  How do I enable DHCP Relay on the 3560?

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Cisco Switching/Routing ::7010 - How To Configure DHCP

Aug 9, 2012

I have couple of questions about Nexus 7010 configuration. how do we configure DHCP like the following example. [code]

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Cisco Switching/Routing :: DHCP Propagation In 3750x

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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Cisco Switching/Routing :: SG 300 VLAN Not Pulling DHCP?

Mar 31, 2013

I have a Cisco SG 300 28 port switch that I have set in Layer 3 mode. I set up a second VLAN on it (vlan 4). I also set up the scope for DHCP on a Windows server for both VLAN's. The problem I am having, is that VLAN 4 is not pulling DHCP at all. The DHCP server is connected to port 1 on the switch, and the specifics are as follows:
 
VLAN 1: 192.168.5.251 subnet 255.255.255.0
VLAN 4: 192.168.55.251 subnet 255.255.255.0
DHCP Server 192.168.5.1

[Code]......

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Cisco Switching/Routing :: SG 100-16 Switch - 2 DHCP Addresses

Jan 11, 2012

I currently have a the following configuration and am unable to get more than 2 DHCP addresses for the devices connected to the Cisco new SG 100-16 Switch.The AP have no trouble handing out DHCP to the wireless clients, but we are unable to get the SG 100-16 to be able to do the same thing to wired clients.  It is currently connected to the 2960-8 in port 1.  We can get 2 devices connected without a problem, but the 3rd machine and beyond do not work.  Also, setting up a static IP does not work.  Using a static will not even allow us to ping or tracer back to any devices beyond the SG 100-16.

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Cisco Switching/Routing :: SW 3750 - ACLs For DHCP

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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Cisco Switching/Routing :: DHCP Snooping On 6506

Mar 2, 2013

I have a problem with high CPU load by DHCP Snooping process on Catalyst 6506 (WS-SUP720-3B, soft: s72033-ipservices_wan-mz.122-18.SXF11.bin). I have it enabled on 15 VLANS, in which there are subscriber devices residing, and sending DHCP requests through Cisco to DHCP server (Cisco acts as DHCP relay, and it's collecting the snooping database, I also use DAI).
 
Snooping database contains 6962 bindings now.
 
CPU load goes high only sometimes, and I don't have a clue, why it's going so high. It can load as high as 45-47% of CPU, like this:

PID Runtime(ms)   Invoked      uSecs   5Sec   1Min   5Min TTY Process
116    81471244 322596368        252 42.95% 43.48% 36.06%   0 DHCP Snooping 

When the load is high, the command: show ip dhcp snooping statistics is showing, that the overall quantity of
Packets Processed by DHCP Snooping is increasing rapidly. In normal situations, it's like 10-20 packets per second, but when the load is high, it's 1000-10000 pps.
 
But when I look at SPAN from my subscriber's VLANS, I don't really see any flood of DHCP requests, or something like that - everything looks as usual. Maybe, some of subscriber's devices are sending incorrect DHCP requests, that are causing packets to loop inside RP, or something like that? How can I detect that thing?
 
Also I thought, that if I enable the ip dhcp snooping trust mode on all of the Catalyst interfaces, the DHCP snooping will not process the subscribers DHCP packets, and I can, by exclusion of interfaces from one to one, detect, from which interface the problem is originating. But this seems to be incorrect, I turned the ip dhcsp snooping trust on all interfaces, and I still get spikes of CPU load by DHCP snooping process. Why it's still examining packets, even on trusted interfaces, is it ok?
 
And one more question - if I disable the ip dhcp snooping globally, will it clear all my existing bindings in snooping database?

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Cisco Switching/Routing :: 2960 - DHCP PC / Not Getting Valid IP

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Facing some DHCP issue. I got my laptop directly connected with Cisco 2960 switch. However it is not getting valid IP.

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