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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How are nameservers selected by hosts? [closed]

When I access my gateway's web interface, there are two sections for primary and secondary DNS servers. It is my understanding that these were selected by (and probably belong to) my ISP. My question ...
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19 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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share mobile data from client to lan [closed]

can help me ? how to configure AP ?
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19 views

Juniper MX80 as layer3 dhcp server

I have this config: set dynamic-profiles CLIENTS-IPoE interfaces demux0 unit "$junos-interface-unit" no-traps set dynamic-profiles CLIENTS-IPoE interfaces demux0 unit "$junos-interface-unit" proxy-...
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32 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
58 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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22 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
63 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
41 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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120 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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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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121 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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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
168 views

meraki bridge mode: dhcp is untagged

We have the following set-up: +------+ +--------+ +--------+ |Router|-----| switch |-----| Meraki | +------+ +--------+ +--------+ | +---------+ ...
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45 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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145 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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78 views

Multiple DHCP Pools in Ubuntu Server with DHCP Relay

I am currently using Cisco SG-350 Series Switch as the DHCP server on the network. I was having 16 VLANs, and my SG350-28 switch was acting as the DHCP server for all the VLANs. All was running fine ...
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37 views

152 bit hardware address in dhcp binding?

When listing MAC addresses on a Cisco ISR DHCP service, I get a long list of hardware addresses, one per IP address, but for one IP I get an address so long it runs onto three lines. The other ...
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1answer
46 views

Cannot ping PC directly connected to switch

I'm trying to configure a new subnet for my users. DHCP is configured on the switch SW1. The topology looks like this : SW1 <===> SW2 <===> PC There is an etherchannel + trunk link between SW1 ...
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1answer
40 views

I have a small managed switch I want to use as the default gateway for my subnet, but something isn't working

Not a networking guy by trade, but I know enough to get myself into some trouble. And I think I've managed it. I need to set up a DHCP server on a PC for a small subnet of 3 or 4 devices. I have ...
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1answer
46 views

DHCP server access problem

what will stop a pc from receiving ip address from DHCP server? Is it STP , VTP , 802.1Q or DTP ? What is the most preferable ?
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4answers
167 views

How do devices connected to a switch get their IPs?

It should go without saying, I'm new and still learning about networking. One of the things I'm not clear on and couldn't find a satisfying answer to, although I've done some digging around, is how ...
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2answers
74 views

In making network changes how would mixing sub nets affect the network

Will hosts with IP address manually assigned as 192.168.0.10/24 or 192.168.1.11/24 continue to function. When the router, DHCP, and switches are now setup to work as 192.168.0.0/22. We in inherited ...
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63 views

Why do we need Dynamic IP, if all devices are already provided with IP address

Why there is a need for DHCP server, when all devices already have a IP allocated to them?
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1answer
60 views

Dynamic DNS and VPN [closed]

I have a few PCs/services that I want to access remotely, which are inside a VPN and gets assigned local IP addresses using DHCP. How can I setup dynamic DNS to access the PCs on their internal VPN ...
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2answers
70 views

What is the Boot File name flag for in DHCP message?

Boot Filename - Optionally used by a client to request a particular type of boot file in a DHCPDISCOVER message. Used by a server in a DHCPOFFER to fully specify a boot file directory and filename....
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47 views

Static IP assignment 3750X - DHCP Override

I have a 3750X that I am running some testing with. I have a VLAN interface that is using 10.10.10.254/21 as it's primary IP and 192.168.10.254/24 as it's secondary IP. See below: interface Vlan10 ...
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1answer
63 views

DHCP options field [closed]

I have a problem understanding the description of the Pad-Option field of DHCP in RFC 1533: 3.1. Pad Option The pad option can be used to cause subsequent fields to align on word boundaries. ...
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2answers
262 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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1answer
228 views

ARP after DHCP discover

Hey All, I was working on DHCP lab As seen in the below figure when I take a pcap between e2 and R1 [in a situation where i shutdown the f0/0 interface on R1 and startup again] I see an ARP ...
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1answer
674 views

What's the difference between DHCP Disabled or Relay on an access point?

I am trying to turn my old router to an access point for the new router, I assigned an IP address in the range of the new one and when I went to disable DHCP there was another option which is Relay ...
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1answer
72 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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2answers
103 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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1answer
565 views

pfsense DHCP lease remember time settings?

pfSense remembers DHCP leases for a quite long time, which is good use on a LAN where the same machines request IP numbers frequently and have a chance to always get the same leases. However on an ...
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2answers
91 views

How to give one pc with dhcp a default-gateway while the rest use static ip and static default-gateway [closed]

I have this topology where the PC0, Server0 and PC4 use static ip and static default-gateway, but one pc is Request DHCP, so i have to use DHCP ip address for him and static ip for the rest, now the ...
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1answer
100 views

How to prevent manual assignment of an IP of VLAN/subnet A when connected to a VLAN/subnet B?

I'm configuring a Cisco router C1111-8p using IOS XE 16.8 with 3 VLANs. VLAN 1: native/management 192.168.0.0/24 VLAN 10 : 192.168.10.0/24 VLAN 20 : 192.168.20.0/24 I haven't set ACLs up yet but ...
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1answer
32 views

Shoretel ST1D Switch not accepting assigned IP

After configuring a Shortel ST1D switch, I connected the LAN1 Port from Shoretel ST1D to my Cisco 4507R switch. I attempted to ping the IP that I set specifically on the ST1D switch and I wasn't able ...
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2answers
388 views

How does a DHCP relay router forward the packet to the server?

We know that routers do not forward broadcast messages. So when a DHCP relay router receives a DHCP Discover message, the destination IP address is going to be 255.255.255.255 because at this stage ...
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2answers
187 views

Cisco DHCP Router

I have come across an issue and I’m not sure on how to resolve. I’m trying to get the router to assign the PC’s within my network IP addresses. I have excluded the ones which i wish to not be used ...
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1answer
28 views

How do devices with static IP behave themselves when plugged to a new network? [closed]

I'm trying to understand how to determine if a device plugged to my PC with Ethernet cable has a static IP. What I'm trying to do is to sniff DHCP packets that it sends and by looking at DHCPDISCOVER ...
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2answers
174 views

What happens when DHCP client and server are on different VLANs [closed]

I'm trying to create a lab on PT and I've attached an image. But for some reason my PC is not able to get an IP address from the DHCP server. There is no issues with layer 1 and layer 2. I checked ...
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2answers
131 views

Client timeout for Cisco IOS Static DHCP Pool

I'm not a network admin, but I have an old Cisco Catalyst 3560 for my network. I've successfully set up a DHCP Pool: ip dhcp pool 192.168.0.0 network 192.168.0.0 255.255.255.0 default-router 192....
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1answer
287 views

Configuring HP Smart Switch and SonicWall with VLAN

I'm trying to configure an HP SmartSwitch with a Dell SonicWall on a VLAN for some computers in our network. The computers in question are on port 37 on the switch. I've created a new VLAN interface ...
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1answer
298 views

No DHCPOFFER message captured in Wireshark

I am looking for the answer why packet captures in Wireshark doesn't contain DHCP offer message. I was trying to capture packets directly on the computer with installed Wireshark and doing a SPAN ...
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0answers
132 views

Cisco ASA: Windows DHCP doesn't bind IP address after failover change active [closed]

Equipment and soft: Two Cisco ASA 5540, ASA ver. 9.1(7)32, active/standby failover DHCP server: Windows server 2016 Anyconnect VPN clients get IP addresses from DHCP servers. Everything works ...
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0answers
83 views

DHCP over Frame Relay [closed]

I have two co-operate buildings. Building A is connected to building B via frame relay. Building A has the main switch server (with VLAN info) and a DHCP server. I need Building B devices to receive ...
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1answer
379 views

Is there such a thing as a “fallback” DHCP server? [closed]

Suppose I have a network 10.0.0.0/24, and a DHCP server that allocates addresses under that network. My question is simple — I have a separate box which is also capable of acting as a DHCP server. ...
3
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1answer
494 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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263 views

Cisco ASA L2TP remote-access VPN with addresses assigned by DHCP

I have an ASA with a working Cisco VPN Client configuration set up. I am trying to phase out the Cisco VPN Client, initially in favour of L2TP. The Cisco Client policy has end-users fetch their ...
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1answer
60 views

Cisco 887VA not handing out IPs to new requests

A few days ago seemingly with no changes (other than we changed the adsl mode on the controller). DHCP has stopped working for 2 of the 3 vlans we have configured on a Cisco 887VA. From the Cisco ...

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