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.
410
questions
1
vote
1answer
15 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 ...
0
votes
1answer
30 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 ...
0
votes
1answer
37 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
0answers
11 views
Is there a way to find all the public ip addresses my pc had for the last months or year? [closed]
Is there a way to find all the public ip addresses my pc had for the last months or year ?
Are they saved somewhere ?
Thanks in advance,
0
votes
0answers
12 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 ...
0
votes
2answers
38 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
0answers
22 views
Cisco FTD DHCP option codes
I have a Cisco ASA 5515-X that is currently running ASA with the FirePOWER module, which cannot sent option code 60 in the DHCP request. My ISP requires me to send this.
Does anyone have FTD 6.4 (or ...
0
votes
0answers
22 views
DHCP helper flow in incorrect config
Discovered a configuration error in our network and would like to double check if the conclusions I drew from it are correct.
Incorrect configuration:
dhcp helper set on VLAN xyz to point at DHCP01 ...
1
vote
1answer
63 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 ...
1
vote
1answer
42 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
0answers
28 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 ...
0
votes
0answers
14 views
Next-server option missing in dhcp server on EXOS switch
I'm trying to utilize the build-in DHCP server on our EXOS switch.
Address pools work as intended. So far so good. But I also need to boot our FOG iPXE server through it. The configuration of the ...
0
votes
1answer
78 views
Cisco IOS Software [Everest], ISR 4331. Vlan+Vrf+Dhcp
I'm looking after to use a setup with that objectives in mind:
Create a subinterface on interface GigabitEthernet0/0/1
create a Vlan and assign it to that subinterface
create a vrrf and assign it to ...
0
votes
1answer
65 views
Cisco ip helper-address
I am looking at the DHCP documentation and i cannot seam to find how to configure the router to use a loopback interface as the relay-agent. My objective is to use option 82 so that the dhcp server is ...
1
vote
2answers
49 views
Per-VLAN DHCP pools on the switch
Let us say I have a switch on which I have created two VLANs 10 and 20. I have set ports 1-10 to be on VLAN 10 and ports 11-20 to be on VLAN 20. Presently the PCs in both VLANs are configured with ...
1
vote
2answers
238 views
General: What is a dynamic gateway, how does it work, where is it used?
I saw this option in my OPNsense gateway configuration, and was hoping someone could shed light on what it is, exactly:
Dynamic gateway policy: [YES/NO]
This interface does not require an ...
0
votes
1answer
40 views
Are new DHCP options sent automatically to clients?
When new DHCP options are configured on a DHCP server (Like NTP and DNS server options) are these sent out to clients automatically?
if clients were provided an infinite lease time and so they would ...
0
votes
0answers
9 views
Cisco RV345P - disable DNS names for DHCP bindings
This is about Cisco RV345P router (non-IOS, it's the Web interface kind).
When the hosts on our office LAN obtain address from DHCP their host name is automatically registered in a local DNS resolver ...
0
votes
4answers
187 views
How the device chooses between multiple DHCP pools?
In a router , you can create and configure multiple DHCP pools each one with its own default route and dns server . And because the DHCP pool configuration is not specific to an interface in a router, ...
0
votes
2answers
34 views
Cisco 2960-CX - Dynamic Management IP over trunk link
I have a Cisco 2960-CX switch mounted in a Mobile CT (hospital owned). This "trailer" moves between my 7 campuses as needed. Is there a way for the switch to obtain an IP address ...
0
votes
1answer
17 views
Question about the rebooting state of the DHCP protocol [closed]
Taking into account this diagram...
I wonder if a device, after a reboot having a previous known configuration, uses it from the start even tho it's still asking to check if it can continue using ...
0
votes
3answers
2k views
how to capture DHCP packets in wireshark
Hy!
I want to capture DHCP packets in Wireshark but I did not receive any. Not my filter wrong, I don't get any. So I think I can't trigger the DHCP communications.
my filters:
dhcp
bootp
udp.port == ...
1
vote
1answer
57 views
Will devices with static addresses, will be disconnected when DCHP 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
1answer
139 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)> ...
0
votes
1answer
180 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
38 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
61 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
31 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
116 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
4answers
155 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
67 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
39 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
40 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 ...
1
vote
1answer
137 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 ...
1
vote
2answers
150 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 ...
3
votes
1answer
68 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
61 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
33 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
2answers
111 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
441 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
32 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
336 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
49 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
589 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 ...
27
votes
8answers
18k 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
1answer
448 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
54 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
792 views
meraki bridge mode: dhcp is untagged
We have the following set-up:
+------+ +--------+ +--------+
|Router|-----| switch |-----| Meraki |
+------+ +--------+ +--------+
|
+---------+
...
0
votes
3answers
100 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
148 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 ...
