Cisco Switching/Routing :: 2960S - How To Setup DHCP Relay For VLan2

May 9, 2013

Windows Server 2008 R2 has two DHCP scopes 192.168.1.x (for data) and 192.168.2.x (for VOIP). The Catalyst 2960-S has Vlan1 for the Data V LAN and V lan 2 for the VOIP network. How do I setup DHCP relay for Vlan2 to get their IPs from the scope on the Windows server?
Used to doing ip helper-address x.x.x.x in other Catalyst switches, but not available here.

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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 and DHCP servers are in, randomly I guess, I get NACK from my DHCP server, and if I look into DHCP logs I got something like this:


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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 :: 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 :: 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 :: 2921 DHCP Relay Agent

Jun 30, 2012

I have a 2921 with 4 segments: [code] My DHCP server is and I need to serve clients from by MAC address and only to that segment.

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Cisco Switching/Routing :: 3560X-24P-S Will Support LLDP / DHCP Relay

Feb 1, 2012

I would like to know cisco 3560X-24P-S will support LLDP & DHCP relay .If it support which IOS feature is required to enbale these features.

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Cisco Switching/Routing :: C3750 DHCP Relay Is No Longer Functioning For Client PCs

May 29, 2012

I have upgraded a C3750G-12S-E to c3750-ipserviceslmk9-tar.122-55.SE5This switch is a distribution layer switch for one of my remote sites.  it contains an ip helper-address on the site vlan's SVI.DHCP relay is no longer functioning for client PCs.  Static address assignment allows full network functionality. I enabled debug ip dhcp server packet. [code] Actually I am betting you upgraded your IOS from something before 12.2(50)SE to 12.2(50)SE or later.  We added enhancement CSCso19800 which will validate DHCP options when we are a relay agent.

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Cisco Switching/Routing :: 7000 Domain Controller IP To Be Allowed For DHCP Relay

May 2, 2013

I have a Nexus 7000 Core Switch , and i need to allow the domain controller ip 10.x.x.x for DHCP relay on switch.

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Cisco Switching/Routing :: Configure Two 3845 Routers To Act As DHCP Server / Relay?

Feb 14, 2012

I am trying to configure two 3845 routers to act as dhcp server and dhcp relay. Clients are connected to the router that relays all dhcp requests to the vrf instance which is used to connect it to the router wich is running dhcp server.
ip vrf dhcp_dns
rd 8:1
 int gi0/0
ip vrf forwarding dhcp_dns
ip address


So far I can see dhcp requests coming from the R1 and dhcp server on R2 replies with the dhcp offer but PC is not getting any ip.

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Cisco Switching/Routing :: Configure 3560 To Force Client To Get IP By DHCP Relay Server?

Jul 30, 2012

How to configure cisco 3560 to force the client only can get ip by dhcp-relay server ?
The company i am working in has 5 vlans which have been set an lay-3 switch(3560), uses the dhcp-relay server .(in svi configuration: ip helper-address X.X.X.X) well , that works ok~
Now , I got my problem: I need to force the client only can get ip by dhcp-relay server, that means if anyone set static IP manunally , he can't really access to anywhere (to provent anyone set static IP with malignancy )
I know if a h3c router , how to set this configuration n svi configuration : dhcp relay security address-check enable )
the how to configure on a cisco 3560 ?

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Cisco Switching/Routing :: ME3800 Stop Forward DHCP Relay Packets Immediately

Mar 29, 2012

I faced with issue on ME3800. [code] With that configuration there is no problem with DHCP Relay packets.But if I add  on interface #xconnect 82.199.1 19.1 77 encapsulation mpls it will stop forward DHCP relay packets immediately. All other traffic transfers without problem.

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Cisco Switching/Routing :: Block All DHCP Packets Through 2960S LAN Base IOS?

Mar 23, 2013

I am trying to block all dhcp packets through 2960S lan base IOS. But when i set no trust interface for dhcp snooping, the dhcp packet source port will be err-disabled.  Is there any other solution to block any DHCP packet through switch without interface or other service outage?Is possible to block DHCP packet through specific VLAN?

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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 :: 3750x / 2960S - How To Setup InterVLan Configuration

Jul 6, 2012

I am trying to setup intervlan configuration and stuck on a problem. Here are the details:
1. Switches Catalyst 3750-x (as core switch) and Catalyst 2960S (as access switch)

2. Both switches have VLAN 20 and VLAN 1 on their database and both are active. BTW, after I figure out how to properly configure interVLAN routing the native VLAN 1 will not be used anymore. This is just an initial test.

3. VLAN 20 SVI interface (IP on 3750 is up and can be pinged from catalyst 2960.

4. VLAN 1 SVI interface (IP on 3750 is up and also can be pinged from Catalyst  2960.

5. Catalyst 3670 can ping a client computer (IP connected to Catalyst 2960.

6.  IP route enabled on 3750

7. Trunking is enabled on etherchannel connecting both 3750 and 2960

8. Client computer in VLAN 20 (connected to 2960) can ping VLAN 20 SVI interface on switch 3560.But, the client computer in VLAN 20 can not reach any computer in VLAN 1 and vice versa. Strangely, the switches which these computers are connected to can ping each other or any connected client copmuters without any problem as described above.

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Cisco Routers :: RV042 Setup - VLAN1 To VLAN2 Access?

Nov 19, 2011

I have 2 VLANs set up and I know they are set as default to not allow one to communicate to the other.  Is there a way to set a rule to allow that?  I'd like VLAN1 to be able to access VLAN2, but not the other way around.

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Cisco Switching/Routing :: Catalyst 3560X-24T-S - Setup DHCP Servers On Layer 3 Switch?

Apr 1, 2012

Do you have the ability to setup DHCP servers on this layer 3 switch? I know I can with my old 3550 switch. Want to upgrade and make sure this model supports setting up dhcp servers on it.

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Cisco Switching/Routing :: 2821 Multicast Routing Relay Basic

Mar 12, 2013

I  start configuring Cisco 2821 router for multicast . First short  description and attached sheme explanation. Let we say  I have small  network with 100 users. One router and Cisco switch 3560. Two VLAN’s,  one for data another for multicast. Data from internet works fine but  now I want to connect multicast servers (or source of more multicast  streams) from another subnet. Router have three interfaces.I expect there should be no problems with multicast configuration, but unfortunately it is not like I expect. What I did ?

First step:  enable multicast routing

Second step: on both interfaces (Fe 0/1 and Fe 0/2)  - ip pim sparse-mode

Third step: configure switch that users are connected to access port in VLAN 222 (temporary to see if multicast work)
When  I start VLC on computer nothing happend. If I try to connect computer  on same subnet where is source of multicast streams it works fine.What  I am doing wrong ? Is there anything about routing ? All subnets are  directly connected. RP is not needed if I have one router or ?

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Cisco WAN :: DHCP Relay With ASR 9000

Feb 6, 2013

I'm having a problem getting DHCP working with an ASR9k as shown in this document. I've successfully implemented very similar setups with some Cisco IOS routers, but the IOS XR on the ASR seems to be defeating me. Router A (happens to be a 3750)A DHCP/BOOTP/TFTP server, connected to router ARouter B - this is the ASR, running software version 4.0.3.Router A and B are connected by a layer-3 link.Router C (happens to be a Broadcom embedded router). It's connected to Router B by a VLAN trunk link.Device 1, this one needs to get its configuration by DHCP/BOOTP/TFTP. It's connected to Router C by a VLAN trunk link.Device 2, this one doesn't need any DHCP/BOOTP/TFTP. It's connected to Router C by a VLAN trunk link (its port is the same as Device 1's)  Device 2 works great - it can ping the DHCP/BOOTP/TFTP server (and vice versa) and everything else it needs.

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Cisco :: DHCP Relay And VLAN Identification

Oct 15, 2012

I have a firewall that I want acting as a DHCP relay. This firewall has a number of VLAN interfaces serving clients. The DHCP relay destination is the IP address of a Windows 2012 Server running Microsoft DHCP which has multiple scopes configured, one for each client VLAN.What I'm finding confusing is how the DHCP will identify the client. Does the DHCP relay insert an identifier of some sort (opt. 54?) based on which VLAN the DHCPREQUEST comes from and then this identifier can be configured to be recognized on the DHCP server?

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Cisco WAN :: 1841 DHCP Relay Through GRE Over IPsec

Mar 17, 2011

I have a data center with virtual desktops and other shared infrastructure serving remote sites, some of which are connected to the data center with GRE over IPsec.
IP address management including DHCP is centralized in my architecture, but I simply cannot figure out how to relay DHCP requests through GRE over IPsec to my DHCP server cluster. I am working with Cisco 800 series VPN peers, and the VPNs are terminated either on a 1841 or a Juniper SRX. Everything else is just fine and dandy, but DHCP is not forwarded across the GRE tunnel.
As a workaround I am forced to use local DHCP pools on the VPN peers, which is extra work from a management point of view, and also precludes static IP address assignment where a local DHCP pool is in a VRF. My LAN devices are mostly thin clients, so I don't care if DHCP stops working when the WAN link fails. As such local pools have no upsides, they are only a tremendous hassle.
My config is very basic, public WAN in global routing table and WAN + GRE tunnel in a VRF. NAT is not used. Here are the DHCP-related configs I have tried:ip helper-address on the LAN gateway, both with and without ip forward-protocol udp bootpcip dhcp pool with relay options configured 

In every case, I can see the UDP broadcasts hit the LAN gateway, but relayed packets never arrive at the other GRE tunnel endpoint let alone the DHCP server.

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Cisco Switches :: SGE 2000 - DHCP Relay

Oct 15, 2009

I have defined several V LAN's and the corresponding IP Addresses on the SGE2000. The static routing works fine. On one V LAN there is a Windows 2003 DHCP Server which I have defined as DHCP Relay Server (Option 82), but no packets are relayed. Has anyone a functional setup, with dhcp relay?

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Cisco Routers :: SRP 527W - How To Configure DHCP Relay

Sep 12, 2012

I know how to disable the DHCP on the SRP527W but i was wondering how do i configure DHCP relay to point to a network DHCP server.

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Cisco Switches :: DHCP Relay On A SGE2000 Switch?

Jun 25, 2012

DHCP Relay on a SGE2000 switch.I have configured two VLANs on the switch, VLAN2 (192.168.10.x/24) and VLAN3 (192.168.9.x/24). I have the switch in Layer 3 mode. I have configured the DHCP relay server of and the DHCP Interfaces as VLAN3. All of the IP Static Routes were generated by the switch.
If I put a client computer on a port that is Untagged VLAN 3 and try to get a DHCP address from the server on an Untagged VLAN 2 port I never get a response back.I have done some packet captures and here is what I have found:

I see the DHCP broadcast on the client computerI see the DHCP Request on the DHCP server coming from the IP assiged to the switch on VLAN 3 ( see the DHCP server respond with a DHCP OfferThe DHCP offer never gets to the client computer I can't seem to get a DHCP address to any system not on the same VLAN as the DHCP server. Option 82 is disable and I did try enabling it, which made no difference.

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Cisco Switches :: SRW248G4P Supports DHCP Relay

Feb 12, 2013

Does SRW248G4P supports dhcp relay?I don't see any option for it with firmware version 1.0.2.

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Cisco Routers :: WRVS4400Nv2 DHCP Relay On 2nd VLAN

Feb 24, 2011

Here's what I'm trying to figure out:
My network is set up such that I have a Wireless Network in VLAN 1, which is the primary network that we use.  The subnet is 10.5.1.x.
My goal is to set up a completely isolated Guest Wireless Network, however it would work best.  What I am trying to do now is I created a seperate VLAN (VLAN 2, IP range 10.5.2.x) and turned on DHCP on the WRVS4400N.  However, in the Guest Network, it is always picking up a 10.5.1.x IP which is handed out by the DHCP server (, Win 2003) and still routing all of the traffic to/from our private network.
Here's What I have set:
Wireless>Security Settings>Guest Network (SSID 2)
Wireless Isolation (between SSID w/o VLAN): EnabledWireless Isolation (within SSID): EnabledSetup>LAN>VLAN 1
Router IP, WLAN IP Relay for>LAN>VLAN 2
Router IP Enabled for 10.5.2.x subnetDHCP Relay option is grayed out (not sure why)Setup>Advanced Routing
Inter-VLAN Routing: Disabled 
Any way to solve this would be fine.  I just do not want traffic routing through our internal network.  Ideally, if I could get the Windows server to hand out 10.5.2.x addresses, that would be perfect, but I'm not sure how to configure it for such. 

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How To Configure Dhcp Relay Agent And How It's Work

Jun 17, 2012

how to configure dhcp relay agent and how it's work

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DHCP Relay And Switch Port Settings?

May 7, 2011

I am actually more of a 3Com guy than Cisco but I like to think I know my stuff and having just discovered this site I hope to join in as it looks a good place.I have a question about the general theroy underneath DHCP relay (IP Helper in the Cisco world I believe!)I've always put the DHCP server in VLAN1 only. A few weeks ago, I repatched the DHCP server in one of our offices (small site, single switch) into a different port by mistake. A few days ago I noticed (when doing something entirely unrelated) that I had left it in a port on both VLANs meant for PC's/phones. So, untagged on VLAN1, tagged on the voice VLAN. It had continued to work properly all that time however.By contrast, at a larger site, a new DHCP server came online and was put on a switch elsewhere in the building and was also put into a port on both VLANs - however things didn't work at all - of course we noticed immediately and changed the port setting to VLAN1 only, and it came back.In the second example, the server was on a different switch to where the main L3 switch for the Voice VLAN was (which also does the DHCP relay), and was connected over a fibre trunk link.Is there any reason why it should work on a single switch on a port on both VLANs, but not when connected over a trunk link? The server does not understand tagging. In the case where it worked, the phones were getting an IP from the correct scope; so the relay obviously must have been working with the server issuing an address based on the GIADDR field.

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Cisco Switching/Routing :: Catalyst 2955 Relay Connector Information

Feb 6, 2012

I come across to use the Catalyst Switch 2955 and it has two Relay Connector with one Major (MAJ) and one Minor (MIN) as below picture.There is command line to trigger these two Relay Connectors. As below command to set the Relay Connector to minor for monitoring the power supply: alarm facility power-supply relay minor
1. My questions are when there is power-supply faulty, the Minor Relay Connctor (right picture) will be short-circuited, right?
2. If we connector the two ports (ports 4 & 5 at the left picture) with a normal cable to drive an Alram Bell (in short-circuiled or closed loop situation), do we need an external power supply to the Alram Bell? Or there will be power supply from Catalyst 2955 to the Alram Bell as well?

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Cisco Switching/Routing :: Relay Agent And Forwarding Query On 2960?

Nov 23, 2011

I need support on understanding and configuring dhcp relay agent And forwarding. Lets say a bunch of TCP/IP devices required a dhcp ip where it is installed on a perticular server to run so. The server having dhcp pool where it provide the devices with IP addresses as he recieve queries from them requesting to release their addresses. On 2960 switch no dhcp configured and ports assigned under specific vlan under those devices. The issue here, if power goes down and booting process started, the devices started to ask the server for ip add and it takes too much time and somehow it does not take ip and those request kind a dropped. As the minimum requirement is to configure relay agent on the switch and forwarding and multicast?

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Cisco VPN :: 880 / 1800 / 2960 - DHCP Relay Through IPSEC VPN Tunnel

Mar 11, 2011

Here is the high-level question, please only respond if you have a conclusive answer with documentation to back it up. It seems simple, but all my research on forums and things have been confusing and conflicting.
When "ip helper-address" is used to enable the dhcp-relay function, will the DHCP packets get relayed through the VPN tunnel (if thats where the DHCP server is?)  This question applies to Cisco IOS Routers and VPN appliances which have a Site-to-Site IPSEC VPN Tunnel to a place that hosts a DHCP server.
I'm using the Cisco 880 and 1800 series routers.  I've already got DHCP relaying through IPSEC tunnels, but so far I've only set it up where my 2960 switch relays the DHCP messages to the VPN router on site (which is a separate device). I want to know if the router can pickup and relay through it's own tunnel natively.

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Cisco WAN :: How To Setup DNS Relay On 877 Router

May 7, 2012

typical ADSL configuration. My ISP only sends out DNS information automatically (PPP) - no static entries. I need to capture this information and relay it to users via DHCP. Currently when I do "ipconfig/ all" all DNS entries are empty.           

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WAN Setup Using Frame Relay?

May 21, 2011

Main site have 8 departments and each department have 60 pc's,remaining sites each have 6 departments and in each department have 40 pc's and in the design of WAN connection you use frame relays and that is the 100% growng hosptals and clock speed is 64000 bits/sec and security must don't access the unautheraised users from out can I do this?

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