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.

Filter by
Sorted by
Tagged with
0
votes
0answers
15 views

Statis IP address changing [closed]

I have a system with three NICs, two NICS have a static IP and one has a DHCP IP. The static IP keeps changing and the config files .xlr keep disappearing. Any ideas? Antivirus?
0
votes
0answers
16 views

Proper configuration for using an old router as an access point/switch? [closed]

So I've moved house and re-setup the network, pretty much the same apart from a different router and new Ethernet cables. And I think I should configure all the infrastructure more suitably and ...
0
votes
1answer
36 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 ...
0
votes
1answer
20 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 ...
0
votes
2answers
50 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 ...
0
votes
0answers
25 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/...
2
votes
2answers
67 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 ...
1
vote
3answers
65 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
votes
1answer
51 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 ...
0
votes
0answers
27 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 ...
0
votes
1answer
35 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 ...
0
votes
1answer
44 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 ...
0
votes
2answers
72 views

Unknow 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
votes
1answer
59 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 ...
1
vote
0answers
17 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 ...
1
vote
1answer
31 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 ...
0
votes
0answers
95 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-...
0
votes
1answer
51 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
votes
1answer
165 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 ...
1
vote
0answers
27 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
votes
1answer
129 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 ...
0
votes
2answers
44 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?
2
votes
3answers
248 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 ...
26
votes
8answers
13k 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 ...
1
vote
1answer
228 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 ...
0
votes
0answers
38 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; } } ...
2
votes
1answer
298 views

meraki bridge mode: dhcp is untagged

We have the following set-up: +------+ +--------+ +--------+ |Router|-----| switch |-----| Meraki | +------+ +--------+ +--------+ | +---------+ ...
0
votes
3answers
46 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 ...
3
votes
2answers
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 ...
0
votes
2answers
223 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 ...
0
votes
1answer
40 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 ...
0
votes
1answer
93 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 ...
0
votes
1answer
60 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 ...
0
votes
1answer
71 views

DHCP server access problem

What will stop a PC from receiving an IP address from a DHCP server? Is it STP, VTP, 802.1Q or DTP? What is the most preferable of these?
0
votes
4answers
177 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 ...
0
votes
2answers
91 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 ...
0
votes
2answers
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?
0
votes
1answer
102 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 ...
0
votes
2answers
300 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....
0
votes
1answer
52 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 ...
0
votes
1answer
88 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. ...
2
votes
2answers
359 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 ...
0
votes
1answer
467 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 ...
1
vote
1answer
2k 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 ...
1
vote
1answer
106 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?
4
votes
2answers
112 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 ...
3
votes
1answer
925 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 ...
1
vote
2answers
120 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 ...
2
votes
1answer
128 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 ...
2
votes
1answer
41 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 ...

1
2 3 4 5
8