DHCP Relay

I have a setup where my ISP router hands out DHCP addresses and my 2 time capsules is used to backing up our mac computers. I´ve installed the TC´s in bridged mode and their ip addresses is from the DHCP. Then today I tried to setup both my TC´s with an ip address just outside the scope, this way I always know what their ip addresses are, useful for some of my other clients that uses them as fileshares. But if I do that it looks like they wont relay DHCP addresses anymore?? If my scope is 192.168.1.10 - 99 and the gateway is .1, the TC´s should agree fine with being .2 and .3. But everyone connected to the TC´s (ethernet and wireless) stops receiving DHCP addresses.. Is this by design or is it a bug. I´ve never seen any other network devices do this??
It would be ok, if I was able to enable the relay again, but I can´t.
Regards

Go back to the start.. something is strange.. I run a number of TC in bridge and they have no issues getting IP and in fact in bridge if there is no dhcp server they will self-assign a 169.254.x.x address. Each time the lease expires the TC should simply find itself an address.. i have set this up with numerous different modems and routers. and not one has had issues. Although it is not unknown for dhcp to fail. You will generally have to do some rather intensive investigation, using a hub or a managed switch where you can mirror the ports and use a utility like wireshark to check dhcp requests.
You stated the ISP is giving you dhcp address.. does this mean you have a block of Public IP addresses?
I didn't think so because you then give the address range as 192.168.1.10-99.. that has nothing to do with the ISP and is purely from the modem router. So what did you mean by that statement??

Similar Messages

Setting up a DHCP relay agent

Hello,
I'm trying to setup a relay agent for an XP client to obtain configuration through 2 routers on a VM LAB
I have 3 Segments/subnets 1,2 and 3
the topology is the following:
1- server 2008 R2 AD DS DC on subnet 1 (192.168.1.0) and a DHCP server with 2 scopes
Internal 192.168.1.0 (subnet1)
external 192.168.3.0 (subnet 3)
2- server 2008 R2 with RRAS installed
Interface 1 pointing to the internal subnet1 192.168.1.0
Interface 2 pointing to subnet2 192.168.2.0
3- server 2003 with RRAS installed
Interface 1 pointing to subnet2 192.168.2.0
Interface 2 pointing to subnet3 192.168.3.0
relay agent installed on Interface 2
(servers/Routers 2 and 3 running RIP v2)
4- XP client on subnet3 (192.168.3.0) and the client trying to obtain config.
The XP client is unable to contact the DHCP to obtain config.
server 2003 relay agent receiving requests with no replies.
How do i get this to work?

Hi,
First, let’s see how DHCP relay agent works:
1. The DHCP client broadcasts a DHCPDISCOVER packet.
2. The DHCP relay agent on the client’s subnet forwards the DHCPDISCOVER message to the DHCP server by using unicast.
3. The DHCP server uses unicast to send a DHCPOFFER message to the DHCP relay agent.
4. The DHCP relay agent broadcasts the DHCPOFFER packet to the DHCP client’s subnet.
5. The DHCP client broadcasts a DHCPREQUEST packet.
6. The DHCP relay agent on the client’s subnet forwards the DHCPREQUEST message to the DHCP server by using unicast.
7. The DHCP server uses unicast to send a DHCPACK message to the DHCP relay agent.
8. The DHCP relay agent broadcasts the DHCPACK to the DHCP client’s subnet.
We can see in the second step, DHCP relay agent send unicast to DHCP server after receiving DHCP request. So confirm unicast communication between DHCP server
and DHCP relay agent works fine. At least ping should be working. You can use the following commend to add the route entry.
Add a static IP route
http://technet.microsoft.com/en-us/library/cc757323(v=ws.10).aspx
The result should be based on your test. If it doesn’t work it just indicates that we cannot configure another DHCP relay agent behind a relay agent.
Hope this helps.

DHCP Relay forwarded to Secondary when Scope is not available in Primaray

Two ip helper-addresses (let suppose DHCPServer1 and DHCPServer2) are defined on each of the branch router, and customer want to divide the load of DHCP request on two different DHCP Servers. The propose solution by customer is to disable some scope from one DHCP Server (DHCPServer1) and define the similar scope in second DHCP Server (DHCPServer2). Does the DHCP Relay request would be forwarded to secondary server (DHCPServer2), if the scope is disabled on first DHCP Server (DHCPServer1)?

The DHCP request is forwarded to all the addresses defined with the ip helper-address command.
So if you have 2 ip helper-addresses then the DHCP request is sent to both at the same time by the router. First one to respond is usually the one accepted by the client.
Jon

ASA 5512-X - VPN & local clients DHCP relaying (DHCP Proxy vs. DHCP Relay conflict)

Hey all,
I have ASA-5512-X serving as general firewall/router. It also serves as AnyConnect SSL VPN gateway (webvpn).
It has ~10 VLANs connected over 1 trunk port. One of the VLANs has DHCP server that shall serve all the VLANs (192.168.16.2).
I'm trying to have the ASA relay DHCP requests from all VLANs to the DHCP server and to also serve VPN clients.
However, according to bug https://tools.cisco.com/bugsearch/bug/CSCsd22469 both DHCP Proxy (webvpn) and DHCP Relay (local interfaces) can't be enabled at the same time.
As VPN clients connect to the same VLANs as local users (eg. VLAN 2 - 192.168.2.0/24) I want to have the very same DHCP server serving both, otherwise it's gonna become a mess.
Note: if I configure DHCP Relay functionality and disable DHCP Proxy - local clients are served fine. If I configure DHCP Proxy (webvpn) and disable DHCP Relay VPN clients are served fine. I therefore consider setup to be correct, just the ASA limitation won't allow me to make it serve both.
Can DHCP Relay also serve VPN clients (no DHCP Proxy enabled)? did I miss something?
Thanks!

Hi,
The only workaround for this issue is to configure the ASA itself to act as DHCP server for vpn clients. You also have the flexibility of using local pool and AAA server. Why exactly do you want to use the same DHCP server for both?
AM

DHCP Relay Cisco SG500X

Hi,
I've create 2 vlan in a cisco SG500X-24 and a DHCP server on vlan 2. I just want to dhcp server assign ip to devices on vlan 3. I've configured the vlan and dhcp server relay commands.
ip dhcp relay address 192.168.1.11
ip dhcp relay enable
ip dhcp information option
interface vlan 2
ip address 192.168.1.250 255.255.255.0
interface vlan 3
ip address 192.168.51.254 255.255.255.0
ip dhcp relay enable
The dhcp server gets the request from pc, and sends a new address, but the offer packet not comes to device. With Wireshark a see like offer dhcp packet can't jump to vlan 3.
It's the first time a work with SMB series, and this never happens with catalyst. I'm turning crazy.
Anyone can help me? Thank you in advances.
Victor.

Hi,
Yes, also I configured ip dhcp relay on intefaces.
Yesterday I found the trouble. I was using the tftpd32 dhcp server, and I tested with a Windows DHCP server and everything works like a champ. I didn't know what have do, and i turned crazy, so I began to change every element on solution, finally the DHCP server that it was the key.
Thank you so much for your answer.
KR!

WRVS4400Nv2 DHCP Relay on 2nd VLAN

Hi,
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 (10.5.1.5, 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): Enabled
Wireless Isolation (within SSID): Enabled
Setup>LAN>VLAN 1
Router IP 10.5.1.1, WLAN IP 10.5.1.3
DHCP Relay for 10.5.1.5
Setup>LAN>VLAN 2
Router IP 10.5.2.1
DHCP Enabled for 10.5.2.x subnet
DHCP 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.
If anyone has any ideas, that'd be great- thanks!
Matt

Yes...here's an answer I got from Cisco's Engineering support:
The issue you reported is a know issue.
Engineering and development are aware of this issue, and have provided the following information:
PROBLEM DESCRIPTION:
If the WRVS4400N is configured with multiple VLANs, and these VLANs are mapped to different SSID, the user cannot use an external DHCP server to provide IP scopes for these VLANs.
Hosts connected to both SSID will obtain IP address from native DHCP server only.
The workaround for this is to use the embedded DHCP server for all VLANs defined on the WRVS4400N.
Note: This is not considered a bug but rather a product limitation. The developer has confirmed the WRVS4400N is functioning as designed.
Regarding a fix:
Due to wireless and trunk switch port using different chip set, it is not possible to provide a fix for this issue.
In future product, Engineering & Dev teams will strive to use the same chip set (same vendor).
This functionality has been targeted for next new Product. No fix will be made on the current hardware.
Note: If this feature/function is mission critical to your deployment, and you would like to recover the cost of the WRVS4400N, please forward the serial number and a copy of the proof of purchase, and we will gladly provide a refund.
Best regards,
Alex Delano

DHCP Relay using Brocade Switches

Hi
I have a large project with 3 UCM cluster with unity cluster and UCCX
The network is a Brocade switch environement,
The Core is using OSPF and distribution is Layer 2.
I have configured the Cluster with a dedicated DHCP and TFTP service.
DHCP relay is not working, but when i configure one of the phones with a static IP address it registers and I have full functionality
When I connect my server dirrectly to the core which is not the design then the dhcp relay works and I get an IP address, but when i traverse the layer2 then i do not get an address.
In the same topology I connected a Windows DHCP server on the same vlan as my UCM cluster and change the relay address to point to the windows dhcp the i do get an address.
In an additional test i configured the same setup on cisco switches then the relay works great.
If anyone has seen or knows of any bug regarding DHCP relay i would be greatful for info
Thanks
Lance

Hi Experts,
i forgot to mention that i was reading an interesting document on Cisco website "network virtualization design guide", and they clearly mentioned the below:
"""VRF-awareness for DHCP-relay functionality is currently not supported on any Catalyst platform, but it is required only for supporting overlapping IP addresses"""
So i would like to ask you if you have any workaround to be done in such deployments
Thank you in advance
Samer Labaky
CCIE # 24675

NAC.OOB.L2.Real IP GW.dhcp-relay issue.

Hello.
I have CAM (manager) which is configured as L2 OOB real-ip gateway. central deployment.
ethernet 0 (trusted) is L3. (ip add x.x.x.x)
ethernet 1 (untrusted) is .1q and several authentication vlans (a,b,c,d) are connected to it.
of cause managed subnets are configured for auth vlans on eth1.
Manager is configured as dhcp-relay.
Is it ok that manager changes dhcp packets to the dhcp server so that it's ethernet 0 ip address (x.x.x.x) becomes the source address of the requests to the dhcp server?
how can dhcp server recognize auth vlan a from auth vlan b if all packets have the single source (x.x.x.x)???
Where could be my mistake?
Regards

Hello varnavsky!
You have to configure vlan mapping (at the CAM) for all authentication vlan! After the authentication and posture validation, the NAC client won't give a new IP address, so the client has to have an IP address from the proper access vlan. When you configure these vlan mappings CAS always acquire an IP address from the proper range.
By(e) Miki

DHCP relay for SGE2010

hi
I have SGE2010 switch in layer 3 mode and im unable to assign IP addresses in second VLAN 2.
My setup
Port 1: TRUNK , VLAN 1 and VLAN 2 --> connected to Cisco 887 FE3 Trunk with VLAn 1 and VLAN 2 and DHCP pool for VLAN2
Port 2: TRUNK , VALN1 and WLAN2 --> Cisco Aironet 1040 LAN WIFI VLAN 1 and Guest WIFI VLAN2
Port 3: Access , VLAN1 Windows DHCP server for VLAN 1 subnet
My LAN WIFI clients can get IP from Windows DHCP server for VLAN 1
My Guest WIFI clients on VLAN 2 cant get an IP from the Cisco 887 router on VLAN 2.
I did try turning on DHCP relay etc but didnt make any difference.
Can anyone give me some pointers on wat im missing ?
Thank you

Hi, if the symptom is that when you assign an IP address to vlan 2 the switch "locks up" then the reason is because the vlan 1 did not have an IP address assigned by user.
To fix that, you'd need to add an IP address for vlan 1 as you like then try to make an IP for the additional vlans.
-Tom
Please mark answered for helpful posts

3000 series and Multiple DHCP scopes (DHCP-relay)

I need to send different DHCP options to users; however, I need to put certain groups in different subnets. Is it possible to setup the concentrator to relay for addresses from different scopes?

- Configuration
- System
- IP Routing
- DHCP Relay
a. Enable 'Enabled' checkbox
b. Select Forward to
c. Address == 192.168.10.8 255.255.255.0
- Address Management
- Assignment
a. Enable 'Use DHCP'
- User Management
- Groups
- Select 'groupA'
- Modify Group
- Click General tab
- Enter 'DHCP Network Scope' x.x.x.x
- Select 'groupA'
- Remove Address Pool
Now I get the following error:
118 02/08/2005 13:29:00.720 SEV=3 DHCPDBG/39 RPT=34
DHCP discover timeout: no response from polled servers (xid 3821297335)
I can ping the server, and it is serving up this scope to other devices (just not from the concentrator)

PXE with IP Helpers/DHCP Relay

I'm a Sysadmin and I have a question about what is best practice in regards to PXE servers. We are currently using DHCP Options for PXE clients (options 66,67). This works for most clients but is not the recommended method from either of the vendors we have used (Microsoft or Symantec). They recommend using IP Helpers / DHCP relay to forward the DHCP discover request to the PXE servers so that the PXE server is getting the actual request. This is more of an issue now with UEFI-based machines where the boot file would be different based on if the client is UEFI.
My Network team is against using IP Helpers and thinks it can cause issues. This doesn't seem to make much sense to me, as from what I understand, all that happens is both the DHCP server and the PXE servers get the DHCP discover and respond with their relevant info. Can someone clarify what, if any, issues there are using multiple IP helpers/DHCP relay with PXE Servers like SCCM & Altiris? Is this not standard practice?

It's very common to use DHCP relays (IP helpers) in order to centralize DHCP infrastructure. Larger organizations will frequently use this approach in order to avoid having to manually edit DHCP configurations at the router or switch level. Having a few servers with a central DHCP configuration for all segments is a good management proposition.
In most environments, there isn't a problem with doing this, but it is a major architectural consideration and not something you just turn on without consideration. This is largely because DHCP works on a broadcast principle. The clients are going to broadcast for the first DHCP server that answers with an acceptable offer, which they will take. If you have a mixture of local DHCP servers and relays, the local servers will respond faster and may not provide the configuration you want to deploy... at best. At worst, you will have a mix of acceptable responses and a lot of potential for conflicting addresses. On any network segment where you're using DHCP relays, the local server needs to be disabled.
It might be worthwhile going back to your network team and asking what sorts of "issues" that they feel the implementation of DHCP relays would cause. There may be something unique to your environment that makes them reluctant to pursue this approach.

SGE2000 DHCP Relay Issue

I am looking for some help with 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 192.168.10.4 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 computer
I see the DHCP Request on the DHCP server coming from the IP assiged to the switch on VLAN 3 (192.168.9.254)
I see the DHCP server respond with a DHCP Offer
The 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.
Any help would be great.
Thanks,
Phil

Hi phil,
Have you created a static route on the DHCP server that points back to the 192.168.9.0/24 network.
The gateway for that network, from the DHCP relay servers perspective, is the VLAN2 IP address of the SGE2000 switch.
i would think that if you tried to ping the VLAN3 switch IP address from the DHCP server now, you will not get a reply.
When you create a static or persistant route in the DHCP server, you then should be able to ping VLAN3 IP address of the switch.
regards Dave

DHCP Relay Server

Has anyone successfully setup Server 2.2.2 to hand out IP addresses on multiple subnets? I have several VLANs and I'd like to have the server handout the addresses so I can manage them all from a single spot.
My router has a DHCP relay option so I've told it to forward DHCP requests to the server. I setup the subnets I have in the Server App and started the service. When I have a client make a DHCP request, the log shows that it recieves the request and makes an offer but the offer never makes it to the client. The server is handing out addresses in the proper subnets but for some reason the client does not recieve the offer.
In wireshark, this is what I see:
Src: 10.33.1.254 --> Dst: 10.33.1.16 --> DHCP Request
Src: 10.33.1.16 --> Dst: 10.33.110.254 --> DHCP Offer
10.33.1.254 is the router on VLAN1 and 10.33.110.254 is the router on VLAN380 (where the client is). The server is offering addresses in the 10.33.110.0 subnet like I want it to. Do I have a misconfiguration in the server or the router?

Well.. as far as I know what you are asking is not possible... :(
Did it help?

VWLC DHCP relay flooding

Hello.
I have a big problem with a vWLC installation and the DHCP relay. I have a interface for guest access in central Switching mode where is a DHCP Server address which is not in the same subnet. The Proxy mode is on, and the vWLC can reach the DHCP over its default gateway on the Interface. When a clients connects to ssid it sends a DHCP request and the controller sends it with its interface ip to the DHCP. So far so good, but the problem is that the vWLC does not send one packet, it sends thousends of same DHCP requests to the Server. The DHCP Server also ansers with thousends of DHCP acks.
When i give the DHCP which is also a vm, a interface in the guest vlan everthing works correct. Does anybody know if there is a problem with DHCP relay over Layer 3?
Regards Stefan
I use the latest verion of vWLC.

Hello.
I have a big problem with a vWLC installation and the DHCP relay. I have a interface for guest access in central Switching mode where is a DHCP Server address which is not in the same subnet. The Proxy mode is on, and the vWLC can reach the DHCP over its default gateway on the Interface. When a clients connects to ssid it sends a DHCP request and the controller sends it with its interface ip to the DHCP. So far so good, but the problem is that the vWLC does not send one packet, it sends thousends of same DHCP requests to the Server. The DHCP Server also ansers with thousends of DHCP acks.
When i give the DHCP which is also a vm, a interface in the guest vlan everthing works correct. Does anybody know if there is a problem with DHCP relay over Layer 3?
Regards Stefan
I use the latest verion of vWLC.

DHCP Relay through another firewall

Hello,
I have set up two ISA Servers in my lab (learning environment).
One faces the internet, the other one is in between the lan and the perimetral network.
Sort of:
LAN <--- ISA2---> DMZ <---ISA1---> INTERNET.
The thing is that the other office connects to ISA1 through a VPN-Site-to-Site, and it goes all fine except that ISA1 cannot take any ip from the dhcp server standing on the lan.
I have read this: http://technet.microsoft.com/en-us/library/cc302680.aspx
But in my lab, there are two isa servers , so I don't know how to send dhcp requests from isa1 to isa2 excepto for broadcast 255.255.255.255 , but the isa1 does not know how to forward that to the dhcp server in the lan.
I am mixed up because I am not an expert and am learning now about this dhcp relay thing now.
Thanks in advance!!
Luis Olías Técnico/Admon Sistemas . Sevilla (España - Spain)

Thanks a lot Keith.
I was all wrong. The relation between perimeter and lan (in ISA2) is route. And as far as I have read, that is how it should be, when no external network is involved.
I have a question, I feel doubtful about: When ISA1 takes the DHCP request, does he make a broadcast petition to 255.255.255.255 or a unicast request directly to dhcp-server machine ? , because the ISA1 machine is a DHCP relay so, when I configured it I
was asked to write the ip of the dhcp server, then maybe it just knows where to send the dhcp requests from the client and does not perfom multicast 255.255.255.255 but unicast to the dhcp server ?
EDITION: In the statistics of dhcp-server, there is no dhcp requests, so the traffic is not reaching it.
I am still digging in. This is difficult for me.
Luis Olías Técnico/Admon Sistemas . Sevilla (España - Spain)

Sonicwall DHCP relay not working

I recently set up a new vlan and am trying to get the dhcp server on the existing vlan to issue IPs. I have no trouble getting dhcp working with the sonicwall as the server, but I can't get it to pass it along to the actual server. I've set up the IP of the server as a trusted DHCP relay host but I don't see anything in the logs for the relay for the test host on the vlan. I tagged the port the server is connected to for the new vlan so I'm lost as to why it isn't working. DNS also isn't working using that server for the lookup. I am able to ping it by IP though. I'm sure it's something simple I'm missing but vlans are new to me so I'm still learning.
This topic first appeared in the Spiceworks Community

I recently set up a new vlan and am trying to get the dhcp server on the existing vlan to issue IPs. I have no trouble getting dhcp working with the sonicwall as the server, but I can't get it to pass it along to the actual server. I've set up the IP of the server as a trusted DHCP relay host but I don't see anything in the logs for the relay for the test host on the vlan. I tagged the port the server is connected to for the new vlan so I'm lost as to why it isn't working. DNS also isn't working using that server for the lookup. I am able to ping it by IP though. I'm sure it's something simple I'm missing but vlans are new to me so I'm still learning.
This topic first appeared in the Spiceworks Community

DHCP Relay

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