The Arista MLS layer 2 switch must have all trunk links enabled statically.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-255979	ARST-L2-000160	SV-255979r882279_rule	CCI-000366	medium
Description
When trunk negotiation is enabled via Dynamic Trunk Protocol (DTP), considerable time can be spent negotiating trunk settings (802.1q or ISL) when a node or interface is restored. While this negotiation is happening, traffic is dropped because the link is up from a layer 2 perspective. Packet loss can be eliminated by setting the interface statically to trunk mode, thereby avoiding dynamic trunk protocol negotiation and significantly reducing any outage when restoring a failed link or switch.
STIG			Date
Arista MLS EOS 4.X L2S Security Technical Implementation Guide			2025-05-19

Details

Check Text (C-255979r882279_chk)

Review the Arista MLS switch configuration to verify that all Ethernet interfaces designated as trunk links are statically configured to specify only member tagged VLAN traffic is allowed and all nonmember VLAN traffic will be dropped unless untagged traffic is associated with the interface's native VLAN. switch#show run | section trunk ! interface Ethernet6 description STIG Static Trunk speed forced 10000full switchport trunk native vlan 2102 switchport trunk allowed vlan 2100-2102 switchport mode trunk ! If trunk negotiation is enabled on any interface, this is a finding.

Fix Text (F-59598r882278_fix)

Configure static Ethernet interfaces for switchport trunk mode. Ensure required VLAN member tagged traffic is allowed and all other VLAN traffic will be dropped unless an associated untagged native VLAN for the Ethernet interface is allowed. switch#configure switch(config)#interface Ethernet6 description STIG Static Trunk speed forced 10000full switchport trunk native vlan 2102 switchport trunk allowed vlan 2100-2102 switchport mode trunk ! switch(config)#interface Ethernet7 description STIG Static Trunk speed forced 10000full switchport trunk native vlan 3102 switchport trunk allowed vlan 3100-3102 switchport mode trunk !