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ConfigProof

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SW-SEC-007MediumCisco Catalyst and Nexus

Ports negotiating trunking (DTP)

At a glance

Base severity

Medium

Area

Interfaces and Segmentation

Platform

Cisco Catalyst and Nexus

Evidence level

Derived0.90

Benchmark reference

Reads the export, not the device

ConfigProof reads a configuration export. This control is evaluated against the objects in that file, and it reports what the file says. It does not connect to the device and sees no traffic, so a finding here describes the configuration, not what the firewall is doing right now.

Why it matters

A device on such a port can negotiate a trunk and reach every VLAN the switch carries (VLAN hopping).

How to fix it

Web interface

The steps below are written for the web interface. A finding raised on your own export carries the same steps with your object names filled in.

  1. Set every user port to switchport mode access and every trunk to switchport mode trunk with switchport nonegotiate.

Command line

Cisco IOS-XE CLI

configure terminalinterface <interface>switchport mode accessswitchport nonegotiateendwrite memory

An example. Values in angle brackets are yours to supply; a finding on your own export fills in the names it read. Typed in configuration mode; copy running-config startup-config saves it, with no separate commit. Read every line first.

Read it back

show interfaces <interface> switchport
Values to fill in1
<interface>
Each affected port
Before you type it2
  • Written from the Cisco IOS-XE 17 and NX-OS 9 and 10 command references and not run on a device: read each line before you paste it.
  • Repeat the interface lines for every affected port, or use interface range.

How to confirm the fix

  • show interfaces switchport shows no port in dynamic auto or dynamic desirable mode.

Limits

  • A Catalyst port with no switchport mode line negotiates by default; such ports are included.

Compliance references

No benchmark recommendation is mapped to this control in this version.

More in Interfaces and Segmentation

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