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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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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27 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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91 views

How do devices connected to a switch get their IPs?

It should go without saying, I'm all new to networking and there is plenty I need and want to learn about. One of the things I'm not clear on and couldn't find a satisfying answer to, although I've ...
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2answers
49 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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54 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
21 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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26 views

Connecting 2 networks virtually [closed]

I am currently working on setting up a small personal network for home use and my own experimentation. I currently have a small network of computers operating from within my home and I have a server ...
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2answers
31 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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31 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
37 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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13 views

WatchGuard interface with secondary router holding WiFi splash page

I have a captive portal splash page I need to be presented to only 1 Open Wireless SSID on a WatchGuard AP controlled via the XTM330. The WatchGuard is not able to present the required splash page ...
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2answers
49 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
58 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
65 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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0answers
31 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
91 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
87 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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52 views

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

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
68 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
21 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
170 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
178 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
27 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
74 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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0answers
92 views

Customized captive portal with external DHCP server [closed]

I am stuck in one issue for which I need your help on this. Actually its bit complex to explan about my situatuion but I will try my best. I am working on customized captive portal on arm processor ...
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2answers
67 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
134 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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14 views

DHCP Layer 2 and Layer 3 [duplicate]

I am having a difficult time to visualize the conceptions of DHCP Discover message in order to receive an IP address sends out a broadcast at both layer 2 and layer 3. Can someone care to explain? ...
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1answer
153 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
57 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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46 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
164 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. ...
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1answer
132 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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0answers
87 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
44 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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1answer
52 views

ip dhcp class command

Here is a DHCP configuration that we have here: ip dhcp class range ip dhcp pool abc network 10.10.10.0 255.255.255.0 default-router ... class range address range 10.10.10.10 10.10.10.254 My ...
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2answers
100 views

Get DHCP IP with subinterface

Router0 has 1 subinterface on gi0/0 and can't get a ip trough dhcp. Is there something I forgot? The configs: Router0(got no ip from dhcp): interface GigabitEthernet0/0 ip address dhcp duplex ...
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1answer
47 views

Dhcp Broadcast Through Switches

Think of a pc connected to switch1. Sw1 is connected to sw2(trunk port on both switches) and sw2 is connected to a router(dhcp server). Pc sends a dhcp broadcast. Does sw1 passes the broadcast through ...
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1answer
52 views

DHCP Broadcast on SVI

Think of a dhcp broadcast going through multiple switches. What happens to that broadcast when it reaches the vlan interface (svi)?
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2answers
59 views

How can TCP be used in order to implement DHCP and under which circumstances is this preferable?

I am pretty new to the computer networking studies and was learning about the DHCP protocol. It is implemented based on UDP, as I've gathered, but is there a way for it to be implemented over TCP? ...
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1answer
47 views

Why aren't we using digital signatures for the DHCP?

Why aren't we using digital signatures for the DHCP in order to stop Rouge DHCP attacks?
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1answer
27 views

faild hardware address for ifd ge-0/0/0 failed on junos-vsrx-12.1X47-D20.7-domestic vmware machine

I have been trying to configure dhcp client on ge-0/0/0, I have asked a question before about it in this link At first the solution provided worked, but when I started the virtual machine again it ...
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0answers
19 views

DHCP Broadcast messages [duplicate]

Why are there so many DHCP broadcast messages while trying to give a computer some network settings? 2.Last,when can these broadcasts be avoided and how are DHCP relay agents related to the whole ...
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2answers
280 views

Importance of DHCP option 12, client host name

The main purpose of a DHCP server is to provide dynamic configuration for a group of hosts (mainly IP, Gateway and DNS). There are several options that can also be sent. Option 12 (client hostname), ...
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1answer
192 views

Configuring DHCP on Juniper junos-vsrx-12.1X47-D20.7-domestic on vmware

I'm preparing for JNCIS-SEC exam. I used junos-vsrx-12.1X47-D20.7-domestic image to create virtual machine in order to practice for the exam. I am following this to configure the vsrx. When I do the ...
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1answer
38 views

Connectivity from DHCP-based machines to servers with static IP addresses on the same gateway

I have Comcast service with 5 static IP addresses, using a Cisco DPC3939B as the cable modem. In addition to the 5 machines with static IP addresses, there are additional devices that get their IP ...
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1answer
49 views

Can a machine be its own DHCP server for another interface?

I was wondering if a single machine (with several network interfaces) can be, at the same time, a DHCP server and a DHCP client, that is the server would dynamically attribute an IP address to an ...
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1answer
103 views

Why do Cisco IOS switches send packets to DHCP servers with zero giaddr field when DHCP snooping is on?

I recently troubleshooted a network where the switch had DHCP snooping turned on and even though the router which was acting as a DHCP server was connected to a trusted port, the client wasn't able to ...
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3answers
95 views

Sonicwall DHCP client option code

Is it possible to set DHCP option codes for the DHCP client (the WAN interface)? I am quite sure that you can send options in a DHCP request, I quote: "This option is used by DHCP clients to specify ...
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2answers
79 views

Sonicwall DHCP Reserved IPs Broken After Expanding Subnet

I've just expanded our subnet at work from /24 to /22 now that we've started running out of IPs. For ease of transition, I left all statically-assigned IPs at their original addresses and moved the ...