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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15 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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30 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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37 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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11 views

Is there a way to find all the public ip addresses my pc had for the last months or year? [closed]

Is there a way to find all the public ip addresses my pc had for the last months or year ? Are they saved somewhere ? Thanks in advance,
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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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2answers
38 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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22 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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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
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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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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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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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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1answer
78 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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1answer
65 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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2answers
49 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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2answers
238 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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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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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
187 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
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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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
57 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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139 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
180 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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38 views

Juniper / SRX-100 / Repurpose old device / Disable DHCP?

I have an old Juniper SRX-100. I want to re-purpose it for my network. I need to extend the network in a new location, so I need more ports. I could use a simple switch, but I have this laying ...
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2answers
61 views

Why we define pool for declaring CISCO router DHCP?

In case declaring DHCP server in CISCO routers, should define pool with network addresses.↓ Example Router(config)#ip dhcp pool net1 Router(dhcp-config)#network 192.168.1.0 255.255.255.0 The router ...
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31 views

VLAN DHCP Relay Agent how to set

dhcp server V10 10.10.10.10 V10 10.10.10.0 V20 10.10.20.0 V30 10.10.30.0 PC1 - V10 PC2 - V10 PC3 - V20 PC4 - V20 PC5 - V30 PC6 - V30 SW1 int f1/0 no sw ip addr 50.50.90.100 255.255.255.0 int f1/...
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2answers
116 views

Security issues with DHCP snooping on cascading switches

Consider the following topology: This image was copied from here and in this article it specifies the following: Remember that port Fa0/24 on SW2 is an untrusted port from DHCP Snooping’s point of ...
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4answers
155 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
67 views

Why can my device not get an ip from DHCP in a network with 2 VLANS of which one has DHCP?

In our company we have a CISCO 2811 Switch accompanied by an HP1920 Switch. Our current configuration consists of 2 VLANS: VLAN-2 that has no DHCP in IP range 192.168.0.0/24 VLAN-5 That contains DHCP ...
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39 views

Why DHCP client doesn't issue a DHCPREQUEST as it has received a DHCPOFFER?

In GNS3 (and using Cisco routers), I've created four subnetworks like the following: The goal is to set up a DHCP server on router R1 and a DHCP relay agent on router R2 in order to make it available ...
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1answer
40 views

Simplest way to achieve single IP communication with IP camera and simple MCU?

I have a product that uses an IP camera and a simple ATmega-based motherboard for general I/O control, managing a very simple web interface, etc. Ideally, I would like to be able to access both of ...
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1answer
137 views

Cisco DHCP relay with Microsoft DHCP server

Current situation: we have a C3850 switch serving DHCP lease to desktop clients without communicating with any upstream DHCP server Objective: We would like the C3850 switch continue to serve DHCP ...
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2answers
150 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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1answer
68 views

How does DHCP over WiFi work?

Specifically - does the AP that the client is authenticated with mediate the communication between client and the DHCP server when the client first joins the network, or does the client talk directly ...
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0answers
61 views

Configue IOS DHCP server to respond to Option 60 class

I have a number of small networks each with about half-a-dozen mostly-fixed hosts. The routers on each network provide DHCP service for the occasional visiting engineer's laptop. I am adding IP ...
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1answer
33 views

Will DHCPRequest get ignored by other computers?

I've been reading about DHCP and see that it uses limited broadcast to send its initial request to reach a DHCP server. I read about limited broadcast too which says it sends the message to every ...
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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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1answer
441 views

No DHCP ACK from Cisco 897

I have a Cisco 897 acting as the DHCP server for a LAN. The problem is that no client is receiving a DHCP ACK. Client sends DHCP discover Cisco responds with DHCP offer (with IP address) Client ...
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0answers
32 views

How does the IP address lease process work? [closed]

Curiosity. When a Computer-A has just received an IP lease, for example 2 hours. And immediately it is turned off for about 30 minutes. And then new devices are connected. Can any of these new devices ...
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1answer
336 views

Cisco IOS: DNS Servers via DHCP

Simple question: I have following switch configuration: interface Vlan1 ip address dhcp end ip domain-lookup I receive and IP and DNS servers along with it from our DHCP server. At least Windows ...
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2answers
49 views

redundant option in DHCP

RFC 2132 defines both subnet mask and broadcast address option. Why there is a Broadcast Address Option (28) in dhcp protocol, when it can be calculated by a client, using subnet mask and ip address?
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3answers
589 views

Why is DHCP client able to accept DHCP Offer packet?

I am seeing a DHCP packet flow, which consists of at least 4 packets: Discovery Offer Request ACK With the discovery packet, client tries to find DHCP server. Since client does not know his own IP ...
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8answers
18k 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
448 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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54 views

There have DHCP relay for different vlans issue in my MX-480 router

I have the network topology: in this topology, in my router, I set the DHCP relay: admin@MX-RE0# show forwarding-options dhcp-relay server-group { smart_group { 103.57.xxx.19; } } ...
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1answer
792 views

meraki bridge mode: dhcp is untagged

We have the following set-up: +------+ +--------+ +--------+ |Router|-----| switch |-----| Meraki | +------+ +--------+ +--------+ | +---------+ ...
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3answers
100 views

Ip phone problem cannot get an ip address from dhcp using other vlans except from vlan 1

i am trying to understand native vlans. when i use vlan 1 it worked and it provides an ip address to my ip phone. When using vlan 100 it does not work even i tried using native trunking on it. please ...
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2answers
148 views

Industrial Ethernet network design

looking for some advice on network architecture for an industrial switchroom with several constraints. Modbus TCP devices are located in motor control centre cells, these need to connect to the ...

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