<div>
First step is to disable admin logins on all your machines... because... anyone with admin privilege can run a DHCP server, accidentally or on purpose.<br />
<br />
Once you do this, then just audit all your machines... because if a rogue DHCP server is running somewhere, debugging related problems will be a nightmare + near impossible.
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First step is to disable admin logins on all your machines... because... anyone with admin privilege can run a DHCP server, accidentally or on purpose.

Once you do this, then just audit all your machines... because if a rogue DHCP server is running somewhere, debugging related problems will be a nightmare + near impossible.

Network Administrator

DP230

<div>
For finding it: netscan makes it easy, one button to show dhcp servers<br />
<a href="https://www.softperfect.com/products/networkscanner/" rel="ugc">https://www.softperfect.com/products/networkscanner/</a><br />
<br />
Mitigation is up to you, depends on what you find I suppose.
</div>


For finding it: netscan makes it easy, one button to show dhcp servers
https://www.softperfect.com/products/networkscanner/ [https://www.softperfect.com/products/networkscanner/]

Mitigation is up to you, depends on what you find I suppose.

<div>
@Aaron, can you give me the screenshot which show rogue DHCP server is detected?<br />
<br />
It looks like any free scanner software
</div>


@Aaron, can you give me the screenshot which show rogue DHCP server is detected?

It looks like any free scanner software

<div>
If the access switch can't do DHCP snooping, but can do ACLs on the L2 interfaces, you may be able to accomplish something similar by denying packets with a source port of 67/udp on untrusted interfaces. What model of switch are you using?
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If the access switch can't do DHCP snooping, but can do ACLs on the L2 interfaces, you may be able to accomplish something similar by denying packets with a source port of 67/udp on untrusted interfaces. What model of switch are you using?

<div>
Hi Jody, core sw is cisco 3850, access sw is cisco SG200
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Hi Jody, core sw is cisco 3850, access sw is cisco SG200

<div>
It's the computer picture next to the lightbulb. One click<br />
<a href="https://www.softperfect.com/products/networkscanner/manual/" rel="ugc">https://www.softperfect.com/products/networkscanner/manual/</a>
</div>


It's the computer picture next to the lightbulb. One click
https://www.softperfect.com/products/networkscanner/manual/ [https://www.softperfect.com/products/networkscanner/manual/]

<div>
Aaron, but is it available in free trial version?
</div>


Aaron, but is it available in free trial version?

<div>
Yes it's available in the free version
</div>


<div>
Setting a long DHCP lease time can help. If you have it set to say 30 days then devices will almost always renew their lease rather than looking for a new DHCP server. <br />
<br />
Other than that, implementing 802.1x will at least prevent users from plugging in a rouge router, or laptop for home.
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Setting a long DHCP lease time can help. If you have it set to say 30 days then devices will almost always renew their lease rather than looking for a new DHCP server.

Other than that, implementing 802.1x will at least prevent users from plugging in a rouge router, or laptop for home.

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<div class="content wysiwyg-content">
Dear experts, if the Access switch is unconfigurable of DHCP snooping, can we do it on Core switch? (The Dhcp is on Core)<br />
<br />
Otherwise, how can we mitigate the rogue DHCP? Thanks!
</div>
</div>


Dear experts, if the Access switch is unconfigurable of DHCP snooping, can we do it on Core switch? (The Dhcp is on Core)

Otherwise, how can we mitigate the rogue DHCP? Thanks!

Mitigate rogue DHCP server in Cisco network

A router is a networking device that forwards data packets between computer networks. Routers perform the "traffic directing" functions on the Internet. The most familiar type of routers are home and small office cable or DSL routers that simply pass data, such as web pages, email, IM, and videos between computers and the Internet. More sophisticated routers, such as enterprise routers, connect large business or ISP networks up to the powerful core routers that forward data at high speed along the optical fiber lines of the Internet backbone. Though routers are typically dedicated hardware devices, use of software-based routers has grown increasingly common.

Routers

A switch is a device that filters and forwards packets of data between LAN segments. Switches operate at the data link layer or the network layer of the Open Systems Interconnection (OSI) Reference Model and therefore support any packet protocol. LANs that use switches to join segments are called switched LANs or, in the case of Ethernet networks, switched Ethernet LANs. A hub is a connection point for devices in a network. Hubs are commonly used to connect segments of a LAN. A hub contains multiple ports; when a packet arrives at one port, it is copied to the other ports so that all segments of the LAN can see all packets.

Switches / Hubs

Cisco PIX is a dedicated hardware firewall appliance; the Cisco Adaptive Security Appliance (ASA) is a firewall and anti-malware security appliance that provides unified threat management and protection the PIX does not. Other Cisco devices and systems include routers, switches, storage networking, wireless and the software and hardware for PIX Firewall Manager (PFM), PIX Device Manager (PDM) and Adaptive Security Device Manager (ASDM).

Cisco

The Dynamic Host Configuration Protocol (DHCP) is an auto configuration protocol used on IP networks and an extension of the Bootstrap Protocol. DHCP allows for computers to be configured automatically to communicate with each other over an IP network without the need for manual setup by a network administrator. The implementation of DHCP relies on a DHCP server to hand out network configuration information to DHCP-capable clients that request an IP address (and other information required or useful in communicating with other devices on an IP network). In addition to an IP address, common configuration information served over DHCP includes a default gateway, subnet mask and DNS sever(s).

DHCP

Networking is the process of connecting computing devices, peripherals and terminals together through a system that uses wiring, cabling or radio waves that enable their users to communicate, share information and interact over distances. Often associated are issues regarding operating systems, hardware and equipment, cloud and virtual networking, protocols, architecture, storage and management.