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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DHCP Discover Broadcast and its IP (255.255.255) [duplicate]

Cheers, I am trying to learn more about DHCP, and when studying about the session that DHCP goes through every one mentions that it broadcasts a discover message at IP: (255.255.255.255) (as seen here ...
0 votes
2 answers
95 views

Question about subinterface DHCP relay CISCO

I want to make 4 PC got DHCP IP address No problem with left side, but right side 2 PC can't get IP automaitic. I think the problem is DHCP Relay. How can I use ip helper-address for subinterface of ...
0 votes
1 answer
247 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)> ...
3 votes
1 answer
222 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?
1 vote
1 answer
43 views

How to configure a router as a dhcp server for vlans throught a Layer 3 switch?

I would like to know what commands to type in the different switches and the router to to make the router function as a dhcp server for each PC in seperate vlans . I know to create the dhcp pools in ...
1 vote
1 answer
31 views

What could be the bottleneck of my load-testing case?

I need to bring up a bunch of my devices in the network to hit some other service, for testing purposes. And I have used GNS3 to simulate that. As you may find in my GNS3 project, I have such ...
2 votes
2 answers
569 views

Cisco 2960 not receiving dhcp from the router

I have a problem with Dhcp of some the Vlans. here is how my network is : I have a router ASR1001, which connects 15 switches(2960) as a ring topology. each switch has a subinterface of the router ...
3 votes
1 answer
128 views

Is there an equivalent of the Cisco/ Cisco esque command "ip helper-address a.b.c.d" on Mellanox switches?

Apologies for my newbie question. I have recently had a Mellanox switch added to the mix. I was using an "IP helper-address" to forward DHCP requests in different VLANs to my DHCP server(s) ...
1 vote
1 answer
109 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 ...
12 votes
7 answers
45k views

Is a DHCP offer packet a broadcast or unicast?

DHCP OFFER is a layer3 broadcast because the server don't know client Ip, but server knows the client mac address. So how it would be the broadcast? If anyone ask me about this? how should I answer? ...
0 votes
4 answers
123 views

How does DHCP work?

I'm carrying out an experiment to test the mechanism behind DHCP. In this topology, I disable the link between the switch and the router. However, the computer still request IP address successfully. ...
4 votes
2 answers
2k views

arp inspection with dhcp snooping

My network Figure is : In this figure switch 3750 is my main switch and all of ACL and vlaning and DHCP server and... comands are in this switch. I want set ARP inspection configs for security in my ...
0 votes
2 answers
2k views

"Protocol Application Invalid" in CISCO IP PHONE 7940! [closed]

I have a boot issue in Cisco IP Phone "Protocol Application Invalid." So I want to update my firmware. I made my PC as TFTP and DHCP Server and connected my PC and IP phone in same vlan, but it is ...
-1 votes
1 answer
43 views

Apply Interface Default Gateway to Entire Device

I feel there may be a very simple term for what I trying to do, but I'm not sure what it is, and it is difficult to search for it in concise words. The shortest description I can come up with: "I ...
2 votes
1 answer
80 views

How does a DHCP server know which network interface and subnet the new IP address should be on

I've read that DHCP servers add a column to your iptable in your router. A new dynamically created IP address with a network interface and a subnet mask. Then the IP address is matched with your MAC ...
3 votes
1 answer
118 views

how to configure dnsmasq client-identifier for juniper prefix host-name

I have a Juniper switch that has a dhcp-client configured like this: show interfaces irb unit 0 family inet dhcp client-identifier { prefix { host-name; } } I ...
0 votes
1 answer
34 views

How can u assign IP addressing for point to multipoint switches that connect to only one router?

I was wondering if I can assign two network address in a LAN while the switches are point to multipoint which connect to only one router. How will me DHCP going? Router - Switch 1 - Switch 2,3,4
0 votes
1 answer
75 views

Configuration of DHCP for multiple vlans

I have the following network on Packet Tracer. The hosts are in different vlans each one. My goal is that the DHCP server can give IP to the hosts. Here is what I made for each vlan (the example is ...
4 votes
3 answers
33k views

How IP helper address works?

How IP helper address works and what is the difference between dhcp and IP helper-address .please explain in brief.
3 votes
2 answers
66 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 ...
4 votes
3 answers
2k views

DHCP Server Port-Based Address Allocation on Cisco switch 2960-x

I am trying to configure DHCP Server on a Cisco 2960-X switch to achieve port-based address allocation. I would like the IP address assigned to any device connected to that port to be the same every ...
0 votes
1 answer
45 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 ...
2 votes
2 answers
856 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
1 answer
215 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 ...
0 votes
1 answer
4k views

Correct way to set up network with multiple routers/access points over fiber/ethernet [closed]

Heading Below is a network map for a network. Router 192.168.0.1 has DHCP enabled. Routers 0.2, 0.3, and 0.4 are connected via their LAN ports to router 0.1 by ethernet cable, and have DHCP disabled ...
0 votes
1 answer
25 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 ...
3 votes
4 answers
261 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 ...
2 votes
1 answer
57 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 ...
1 vote
1 answer
94 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....
0 votes
0 answers
56 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 ...
0 votes
1 answer
211 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 ...
2 votes
0 answers
328 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 ...
0 votes
1 answer
58 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. ...
0 votes
2 answers
107 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 ...
2 votes
1 answer
109 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 ...
1 vote
1 answer
85 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 ...
1 vote
1 answer
113 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 ...
0 votes
0 answers
17 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 ...
3 votes
1 answer
3k 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 ...
27 votes
8 answers
26k 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 ...
2 votes
1 answer
6k views

How to configure DHCP Relay Agent with multiple VLANs?

I have a network with 2 routers. Router 0 is a DHCP server and Router 1 I assume should be a relay agent. The routing protocol I use is EIGRP. The problem is that PC in vlan 15 and vlan 20 cannot get ...
2 votes
1 answer
2k views

meraki bridge mode: dhcp is untagged

We have the following set-up: +------+ +--------+ +--------+ |Router|-----| switch |-----| Meraki | +------+ +--------+ +--------+ | +---------+ ...
2 votes
1 answer
2k views

Can I use PPPoE and DHCP simultaneously?

In terms of subscriber management, I understand there are two major approaches - DHCP and PPPoE. I know I'm being very general, so give me some rope. If using DHCP, RADIUS/AAA will authenticate the ...
1 vote
2 answers
886 views

Switch0 is configured as DHCP server but not working?

Here I am not able to obtain ip automatically using DHCP. Here is configuration of swtich0 which is having DHCP Server. Switch#sh run Building configuration... Current configuration : 1237 bytes ! ...
2 votes
3 answers
1k views

can a cisco ASA be configured as a DHCP server for a VLAN on a subinterface? and route packets between VLANs?

We are in the process of planning to phase out a Sonicwall tz205 in our office. i am hoping to replace it with a CISCO ASA 5516 specifically. We have three networks in house the main production ...
1 vote
1 answer
68 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 ...
1 vote
0 answers
46 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 ...
2 votes
3 answers
883 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 ...
1 vote
2 answers
489 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 ...
2 votes
4 answers
26k views

DHCP server for multiple VLANs

Good afternoon, I'm learning how to build a network, and I'm trying to add a DHCP server for all VLANs, but I don´t understand how to make it work for all hosts regardless of whether they are on the ...

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