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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35 views

Do IPv6 addresses have better persistence with DHCPv6?

I have a LAN with about 25 devices that occasionally grab each other's IP address via DHCPv4. I know there are certain lease time limits and it can be set to very long periods to work it around to an ...
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2answers
51 views

IRDP protocol nowadays

I'm considering to remove rdisc tool from iputils project (see https://github.com/iputils/iputils/issues/363). This tool implements ICMP Internet Router Discovery Protocol (IRDP). Is IRDP really ...
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1answer
64 views

Configure dhcp relay agent and router on stick

I need help. I don't know what i did wrong because i have configured the dhcp pool, subinterfaces and dhcp relay agent. Gateway pc uses static ip address while Branch pc acquired their ip address ...
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1answer
20 views

Assigning static IPs to VoIP phones in packet tracer

Is there a way to assign IPs and dn to VoIP phones in a network configuration without using DHCP? Such that if I have PCs and VoIP phones connected to the same switch, which is connected to a router ...
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4answers
225 views

How to add two VLANs for DHCP Pool

Currently one of my customer has DHCP pool created in Cisco Switch and ip address range is 192.168.25.0/24 (This is a VLAN). Now they have 230 devices and They are going to increase device count by ...
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1answer
31 views

Assigning static IP address from the DHCP pool range on Cisco 800 series

What happens if I assign a static IP address to a device in a LAN where there is an active DHCP server and the address falls within the configured DHCP pool and DHCP server is Cisco 800 Series? Most ...
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0answers
37 views

Cisco DHCP using dynamic updates

I would like to use a configuration on a Cisco router that allows for clients to resolve the names of other clients without the use of mDNS. I have following configuration: roTST01#show running-config ...
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1answer
106 views

Cisco IOS - Delay DHCP offers

I have two routers in the same subnet that have a HSRP configuration in order to take over, if one of the device fails. There is the same DHCP configuration on both devices: ip dhcp pool LAN network ...
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0answers
94 views

Communication between subnets on Sonicwall firewall

I have a Sonicwall TZ-350. X0 is the default LAN with IP 192.168.10.1, and X1 is the WAN. I've set up a second local subnet on X2 with IP 192.168.20.1 for a single NAS device (no switch; the device is ...
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1answer
46 views

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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1answer
43 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
69 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
78 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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0answers
16 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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2answers
75 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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0answers
41 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
95 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
50 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
35 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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0answers
29 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
211 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
134 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
107 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
572 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
41 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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4answers
623 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
47 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
37 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
5k 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
84 views

Will devices with static addresses, will be disconnected when DHCP 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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1answer
198 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
455 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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1answer
55 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
64 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 ...
2
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2answers
157 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
272 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 ...
2
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1answer
105 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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0answers
72 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
41 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
249 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
268 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 ...
3
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1answer
138 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
112 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
35 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
135 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 ...
3
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1answer
603 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 ...
2
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0answers
34 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 ...
2
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1answer
458 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
54 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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