Questions tagged [dhcp]

For questions about DHCP in in relation to network devices. For instance, you are setting up DHCP on a layer 3 switch.

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DHCP Packet Drops on Return

The DHCP packet makes it from the Security computer all the way to the DHCP server and back to Router1 but gets stuck there. All all packets make it across when the device has a static ip assigned. ...
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18 views

Machine cannot pickup DHCP, however with static IP gets internet, yet cannot ping [closed]

I have a rather complex issue for you guys, Below is the network topology for a small business I help with networking and computer setups, etc. The end PC on the chain is actually a CNC machine for ...
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2answers
46 views

IP Snooping\ARP Inspection With Static Devices On DHCP VLAN

Consider this network: I have enabled DHCP snooping on my system. Switch A has the DHCP connected and the port on VLAN 70 for DHCP has been trusted to allow for reading the database and passing ...
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1answer
26 views

Does an IPv4 DHCP Relay Agent care about Option 80 (rapid-commit)

I'm trying to figure out if an IPv4 DHCP Relay Agent needs to care about a rapid-commit (Option 80) included in a DHCP Discover. My understanding is that the Relay Agent is supposed to simply converts ...
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1answer
50 views

How does a device receive default gateway IP address?

When and how does a device get information about default gateway in LAN? I know you can define default gateway statically, but which protocol is used when it is not statically defined? Is it from ...
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1answer
43 views

DHCP Help 3560-CX + Aruba AP515

The problem VLAN 100 is not assigning IP address to the SSID Guest from the AP, but Aruba is Tagging the SSID to be VLAN 100. How do I get the Switch to assign the DHCP? On the switch, it seems to ...
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12 views

Arp Access-List Without An Interface [duplicate]

I have dhcp snooping an arp inspection setup on my VLAN. I have a number of clients that need to be statically set on this VLAN but still plug into a DHCP access port on the VLAN. I have ip dhcp ...
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1answer
2k views

Host IP address vs gateway IP address vs DHCP IP address

What is the difference between a host IP address, a gateway IP address, and a DHCP IP address when setting up networking devices? For example, when configuring a virtual network adapter for my VM, I ...
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8answers
19k views

Why does DHCP use UDP and not TCP?

DHCP uses UDP as its transport protocol. DHCP messages that a client sends to a server are sent to well-known port 67 (UDP—Bootstrap Protocol and DHCP). DHCP Messages  that a server sends to a client ...
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1answer
6k views

How to configure DHCP Relay Agent with multiple VLANs?

I have a network with 2 routers. Router 0 is a DHCP server and Router 1 I assume should be a relay agent. The routing protocol I use is EIGRP. The problem is that PC in vlan 15 and vlan 20 cannot get ...
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1answer
63 views

How does Network Layer behave when client received a unicast DHCP offer?

I went through various stack exchange post to understand the concept of DHCP offer when it comes as a unicast to client from the DHCP server. A server can send a unicast DHCP offer since it knows the ...
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23 views

Cisco FTD DHCP option codes

I have a Cisco ASA 5515-X that is currently running ASA with the FirePOWER module, which cannot sent option code 60 in the DHCP request. My ISP requires me to send this. Does anyone have FTD 6.4 (or ...
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1answer
830 views

meraki bridge mode: dhcp is untagged

We have the following set-up: +------+ +--------+ +--------+ |Router|-----| switch |-----| Meraki | +------+ +--------+ +--------+ | +---------+ ...
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1answer
2k views

Can I use PPPoE and DHCP simultaneously?

In terms of subscriber management, I understand there are two major approaches - DHCP and PPPoE. I know I'm being very general, so give me some rope. If using DHCP, RADIUS/AAA will authenticate the ...
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2answers
521 views

Cisco 2960 not receiving dhcp from the router

I have a problem with Dhcp of some the Vlans. here is how my network is : I have a router ASR1001, which connects 15 switches(2960) as a ring topology. each switch has a subinterface of the router ...
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22 views

DHCP helper flow in incorrect config

Discovered a configuration error in our network and would like to double check if the conclusions I drew from it are correct. Incorrect configuration: dhcp helper set on VLAN xyz to point at DHCP01 ...
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1answer
463 views

NXOS DHCP Relay - overwriting Option 54 (Server Identifier) differently in DHCPDISCOVER vs. DHCPREQUEST?

I'm trying to sort a DHCP relay problem in a VLXAN/EVPN environment (Cisco N9K, NXOS 9.3.2). We seem to be able to get DHCPDISCOVERs through to the server and DHCPOFFERS back from there. DHCPREQUESTs ...
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2answers
710 views

Switch0 is configured as DHCP server but not working?

Here I am not able to obtain ip automatically using DHCP. Here is configuration of swtich0 which is having DHCP Server. Switch#sh run Building configuration... Current configuration : 1237 bytes ! ...
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3answers
946 views

can a cisco ASA be configured as a DHCP server for a VLAN on a subinterface? and route packets between VLANs?

We are in the process of planning to phase out a Sonicwall tz205 in our office. i am hoping to replace it with a CISCO ASA 5516 specifically. We have three networks in house the main production ...
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1answer
42 views

Is it possible to configure DHCP on a router or UTM firewall for the multiple VLANs on L3 Switch?

I'm working on expanding our office network to accommodate more users/devices. Currently we have the DHCP configured on a UTM firewall(cyberoam ing50) device(cum router) providing IP addresses for ...
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0answers
28 views

1941W wireless clients losing DHCP IP address [closed]

I am attempting to 'extend' a 192.168.1.0\24 network with an experimental network 192.168.10.0\24 using a 1941W router. I have configured 1941W to distribute a 192.168.10.0\24 network, with WLAN ...
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1answer
141 views

Best practice / advice for cisco 3560 behind Virtualised OPNsense

Currently I run the below scheme. The problem is that when ESXi is down it takes down all the network with it, so I have to boot up another router to log in to it. WAN > OPNsense (in ESXi)> ...
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1answer
127 views

How to implement port security in SDN using pox controller and ovs?

How can I defend against DHCP starvation attacks or MAC spoofing in an SDN environment?
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14 views

Next-server option missing in dhcp server on EXOS switch

I'm trying to utilize the build-in DHCP server on our EXOS switch. Address pools work as intended. So far so good. But I also need to boot our FOG iPXE server through it. The configuration of the ...
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3answers
558 views

DHCP on CISCO 3850

I would like to configure the DHCP server on CISCO 3850, and reserve around 100 static IP for servers After doing research found that I need to create individual pool for each static maping like ...
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2answers
152 views

Unknown DHCP problem

Sometimes in my network I have some DHCP problem, the clients don't receive their IP. The problem seems connected with the switch because, for example, if I change the switch port of the client the ...
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4answers
21k views

DHCP server for multiple VLANs

Good afternoon, I'm learning how to build a network, and I'm trying to add a DHCP server for all VLANs, but I don´t understand how to make it work for all hosts regardless of whether they are on the ...
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3answers
5k views

Trying to get DHCP working across three VLANs

I have a packet tracer file with 3 switches and 3 VLANs for a school. It is divided up into VLAN 10, 11 and 12. VLAN 10 is for classrooms 1 and 2, VLAN 11 is for classrooms 3 and 4, and VLAN 12 is for ...
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1answer
87 views

Cisco IOS Software [Everest], ISR 4331. Vlan+Vrf+Dhcp

I'm looking after to use a setup with that objectives in mind: Create a subinterface on interface GigabitEthernet0/0/1 create a Vlan and assign it to that subinterface create a vrrf and assign it to ...
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2answers
332 views

Vlan cannot get DHCP address from using Router and L3 Switch

Simplified diagram of a larger network, but I'm having trouble getting DHCP from the router. Going into simulation mode in packet tracer, I'm seeing an error on the layer 3 switch saying "There is no ...
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2answers
491 views

How VLAN devices will get automatically IP from DHCP server

I have one Windows server 2012R2 which has 10.219.1.1 IP address & I also have Cisco Catalyst 2960-X Series which is layer 2, we managed to do inter VLAN routing by updating its firmware, where we ...
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3answers
153 views

Interface VLAN IP address not on exclude list?

Does an IP address need to be included in a ip dhcp excluded-address x.x.x.x if its already included in an interface vlan? Examples: ip dhcp excluded-address 10.3.8.1 10.3.8.20 interface Vlan30 ...
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2answers
247 views

General: What is a dynamic gateway, how does it work, where is it used?

I saw this option in my OPNsense gateway configuration, and was hoping someone could shed light on what it is, exactly: Dynamic gateway policy: [YES/NO] This interface does not require an ...
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3answers
3k views

How to enable DHCP Cisco router

This is what I have done in my GNS3 R3 - Router R4 - Switch I have installed GNS3 and trying to enable on Router as mentioned above depict. How to enabled DHCP on Cisco router R3 ?
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1answer
70 views

Cisco ip helper-address

I am looking at the DHCP documentation and i cannot seam to find how to configure the router to use a loopback interface as the relay-agent. My objective is to use option 82 so that the dhcp server is ...
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4answers
205 views

How the device chooses between multiple DHCP pools?

In a router , you can create and configure multiple DHCP pools each one with its own default route and dns server . And because the DHCP pool configuration is not specific to an interface in a router, ...
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2answers
52 views

Per-VLAN DHCP pools on the switch

Let us say I have a switch on which I have created two VLANs 10 and 20. I have set ports 1-10 to be on VLAN 10 and ports 11-20 to be on VLAN 20. Presently the PCs in both VLANs are configured with ...
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3answers
2k views

how to capture DHCP packets in wireshark

Hy! I want to capture DHCP packets in Wireshark but I did not receive any. Not my filter wrong, I don't get any. So I think I can't trigger the DHCP communications. my filters: dhcp bootp udp.port == ...
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1answer
40 views

Are new DHCP options sent automatically to clients?

When new DHCP options are configured on a DHCP server (Like NTP and DNS server options) are these sent out to clients automatically? if clients were provided an infinite lease time and so they would ...
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3answers
317 views

Can you keep DHCP addresses from your ISP

I have my modem configured for bridge mode. I get one IPv4 for my router and one goes to my server for public access. If I static assigned these IPv4 address would I keep them as long as no one else ...
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0answers
9 views

Cisco RV345P - disable DNS names for DHCP bindings

This is about Cisco RV345P router (non-IOS, it's the Web interface kind). When the hosts on our office LAN obtain address from DHCP their host name is automatically registered in a local DNS resolver ...
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4answers
24k views

Cisco APs ignore DHCP Option 43 and use CAPWAP UDP broadcasts

Background I am trying to redeploy Cisco 1242 LWAPs on new Cat4507R+E switches, which means the IP address of the WLC is changing for that LWAP. For some reason, I have to configure ip helper-...
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2answers
34 views

Cisco 2960-CX - Dynamic Management IP over trunk link

I have a Cisco 2960-CX switch mounted in a Mobile CT (hospital owned). This "trailer" moves between my 7 campuses as needed. Is there a way for the switch to obtain an IP address ...
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1answer
17 views

Question about the rebooting state of the DHCP protocol [closed]

Taking into account this diagram... I wonder if a device, after a reboot having a previous known configuration, uses it from the start even tho it's still asking to check if it can continue using ...
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4answers
161 views

Assigning IP addresses to multiple switches

Thank you in advance for taking the time to read my question, i appreciate it. I am in need of help on IP assigning to 4 brand NEW Araknis switches that I am replacing with the current netgear/tp-link ...
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1answer
59 views

Will devices with static addresses, will be disconnected when DCHP Server is changed?

In my office network, the DCHP Server is set to 192.168.0.1/24. I want to increase the available pool, so I am thinking update the above setting to 192.168.0.1/23 in order to have: Network: 192.168....
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2answers
111 views

Correctly Setting up DHCP for Intervlan Routing

I am currently building a network and would like my two switches connected to my router to automatically assign ip addresses through DHCP pools to my PC's and devices. I have 4 separate VLans being ...
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2answers
1k views

VLANs allowed vs VLANs active — cannot pull DHCP over WiFi

I am trying to set up a new WLAN. Cisco 5508 controller. W2K8R2 for DHCP. Why would VLAN 600 not appear as active in management domain? I have an AP (Aironet 1041) assigned to VLAN 600. I am unable ...
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1answer
188 views

Some mobile clients are unable to connect to UniFi AP mysteriously

We have two UniFi Controllers, one contains the main internet its directly connected to the fibre and then we give internet to the second controller using LAN connection, internet works fine in main ...
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6answers
37k views

Is a DHCP offer packet a broadcast or unicast?

DHCP OFFER is a layer3 broadcast because the server don't know client Ip, but server knows the client mac address. So how it would be the broadcast? If anyone ask me about this? how should I answer? ...

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