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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18
votes
4answers
24k views

Cisco APs ignore DHCP Option 43 and use CAPWAP UDP broadcasts

Background I am trying to redeploy Cisco 1242 LWAPs on new Cat4507R+E switches, which means the IP address of the WLC is changing for that LWAP. For some reason, I have to configure ip helper-...
12
votes
7answers
15k views

DHCP relay problem on interfaces secondary network

A secondary network was configured on an interface of a Cisco 2621 router and the ip helper-address commands put in place but no clients of that secondary network could pull DHCP addresses. We swapped ...
3
votes
4answers
3k views

How does DHCP assign an IP address?

I understand that IP address is a unique address to identify a machine in a network. But for the first time when i Plug in say ethernet cable of a network to my PC's Ethernet Port, how the IP address ...
15
votes
4answers
40k views

How are two “ip helper-address” statements handled?

I've discovered a subnet with two "ip helper-address" statements. This is not our normal configuration. interface Vlan300 ip address 10.1.3.2 255.255.255.0 ip helper-address 10.2.1.10 ip helper-...
9
votes
3answers
23k views

Assign an IP address based on switch port

Short: I want DHCP server to assign a preconfigured IP address based on a port (on a switch, ideally) a device is connected to. Long: My situation: I am building an automated indoor farm (for ...
27
votes
8answers
19k 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 ...
5
votes
5answers
1k views

How we can assume which network protocol is working in which OSI Layer?

For a long time, I have this kind of silly question: How we can say some network protocols are working in X layer of the OSI model? For example, HTTP working in L7 of OSI, OSPF is L3, ICMP is L4, TCP ...
18
votes
4answers
8k views

Can DHCP Server determine client's OS? [closed]

Is it possible for the DHCP Server to determine the client operating system? I'm working on a monitoring tool for gateways on local networks that is web-based and would like to be able to somehow ...
16
votes
4answers
68k views

Best practice using Cisco's “ip-helper” for DHCP?

Our topology is such that we have two 4510's in our IDF closets. Each switch has a data VLAN and a voice VLAN. The switches are layer 2 trunked to the core, where the VLAN interfaces are, routing ...
14
votes
5answers
12k views

Duplicate IP Address - which one wins?

If there's a duplicate IP address, which one "wins"? First, last, flaps, neither?
10
votes
4answers
18k views

Setting up DHCP server on the router or on the switch?

We're using the Cisco 1921/K9 with a SG300 L3 switch. Does one set up DHCP server on the router or on the SG300? If both is capable, what is the reason to choose one over the other? Note: I have 4 ...
4
votes
1answer
634 views

ARP Destination address (internetwork)

Let's say i have the following WAN: Suppose that all arp tables are empty and that E wants to send a packet to A. The E will send an arp request with destination ip of Router 2(unicast), get its mac ...
4
votes
2answers
2k views

Some question about the relationship between VLAN , DHCP and subnet

I am new here and very interested in computer networks. From a book, I have some questions, for which I need help. question1: Can there be only one working DHCP server in one VLAN? question2: Can ...
3
votes
1answer
378 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 ...
3
votes
2answers
181 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....
3
votes
1answer
842 views

Routing Between VLANs on Cisco 1921

I have setup a new VLAN for VoIP phones that are being installed. I would like to segment their traffic to Subnet 10.20.77.0/24. I added an IP address to the DHCP server of 10.20.77.11 to help serve ...
2
votes
2answers
122 views

Wireless LAN Controller

I have a Cisco 2500 series WLC, and a 1700 series LWAP. In this case, what provides the AP the DHCP IP address, my router or the WLC?? There is already a PoE port in the WLC, yet when I connect my ...
2
votes
1answer
5k views

How to configure DHCP pools for 2 VLANs/subnets sharing a switch

I've set up DHCP pools on a layer 3 switch that goes out to 13 layer 2 switches. Most of which have their own subnet and VLANs, and everything works fine when that's the case. But when there are two ...
1
vote
1answer
46 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 ...
1
vote
1answer
72 views

unable to route traffic 2 switches deep (3 tier design)

so for simplicity sake in testing this configuration, I have a sample project that looked like this: breakdown: Configurations vlans configured on multilayer switch which is also vtp server: vlan ...
1
vote
2answers
4k views

How Can I configure DHCPv6

I want to config one DHCPv6 server using Packet Tracer and with multiple routers, the router takes IP addresses from a server and distribute to computers .I have done that with IPv4 using IP helper ...
1
vote
1answer
593 views

Help this problem with Dhcp Server with two switches

I will try to explain my problem. I am trying that Switch 1 can give dhcp for pcs but i cannot, in Switch 0 I can give dhcp server in the pcs. sorry for my bad english ROUTER ! version 15.1 no ...
0
votes
2answers
56 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 ...
0
votes
2answers
113 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 ...