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XCCDF
Arista MLS EOS 4.2x L2S Security Technical Implementation Guide
Arista MLS EOS 4.2x L2S Security Technical Implementation Guide
An XCCDF Benchmark
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19 rules organized in 19 groups
SRG-NET-000193-L2S-000020
1 Rule
The Arista MLS layer 2 switch must be configured for Storm Control to limit the effects of packet flooding types of denial-of-service (DoS) attacks.
Medium Severity
Denial of service is a condition when a resource is not available for legitimate users. Packet flooding distributed DoS (DDoS) attacks are referred to as volumetric attacks and have the objective of overloading a network or circuit to deny or seriously degrade performance, which denies access to the services that normally traverse the network or circuit. Volumetric attacks have become relatively easy to launch by using readily available tools such as Low Orbit Ion Cannon or by using botnets. Measures to mitigate the effects of a successful volumetric attack must be taken to ensure that sufficient capacity is available for mission-critical traffic. Managing capacity may include, for example, establishing selected network usage priorities or quotas and enforcing them using rate limiting, Quality of Service (QoS), or other resource reservation control methods. These measures may also mitigate the effects of sudden decreases in network capacity that are the result of accidental or intentional physical damage to telecommunications facilities (such as cable cuts or weather-related outages). Satisfies: SRG-NET-000193-L2S-000020, SRG-NET-000362-L2S-000024, SRG-NET-000512-L2S-000001
SRG-NET-000362-L2S-000021
1 Rule
The Arista MLS switch must have Root Guard enabled on all switch ports connecting to access layer switches and hosts.
Low Severity
Spanning Tree Protocol (STP) does not provide any means for the network administrator to securely enforce the topology of the switched network. Any switch can be the root bridge in a network. However, a more optimal forwarding topology places the root bridge at a specific predetermined location. With the standard STP, any bridge in the network with a lower bridge ID takes the role of the root bridge. The administrator cannot enforce the position of the root bridge but can set the root bridge priority to 0 in an effort to secure the root bridge position.
SRG-NET-000362-L2S-000022
1 Rule
The Arista MLS layer 2 switch must have BPDU Guard enabled on all switch ports connecting to access layer switches and hosts.
Medium Severity
If a rogue switch is introduced into the topology and transmits a Bridge Protocol Data Unit (BPDU) with a lower bridge priority than the existing root bridge, it will become the new root bridge and cause a topology change, rendering the network in a suboptimal state. The STP PortFast BPDU guard enhancement allows network designers to enforce the STP domain borders and keep the active topology predictable. The devices behind the ports that have STP PortFast enabled are not able to influence the STP topology. At the reception of BPDUs, the BPDU guard operation disables the port that has PortFast configured. The BPDU guard transitions the port into a disabled state and sends a log message.
SRG-NET-000362-L2S-000023
1 Rule
The Arista MLS switch must have STP Loop Guard enabled on all nondesignated STP switch ports.
Medium Severity
The Spanning Tree Protocol (STP) loop guard feature provides additional protection against STP loops. An STP loop is created when an STP blocking port in a redundant topology erroneously transitions to the forwarding state. In its operation, STP relies on continuous reception and transmission of BPDUs based on the port role. The designated port transmits BPDUs, and the nondesignated port receives BPDUs. When one of the ports in a physically redundant topology no longer receives BPDUs, the STP conceives that the topology is loop free. Eventually, the blocking port from the alternate or backup port becomes a designated port and moves to a forwarding state. This situation creates a loop. The loop guard feature makes additional checks. If BPDUs are not received on a nondesignated port and loop guard is enabled, that port is moved into the STP loop-inconsistent blocking state.
SRG-NET-000362-L2S-000025
1 Rule
The Arista MLS layer 2 switch must have DHCP snooping for all user VLANs to validate DHCP messages from untrusted sources.
Medium Severity
In an enterprise network, devices under administrative control are trusted sources. These devices include the switches, routers, and servers in the network. Host ports and unknown DHCP servers are considered untrusted sources. An unknown DHCP server on the network on an untrusted port is called a spurious DHCP server, any device (PC, Wireless Access Point) that is loaded with DHCP server enabled. The DHCP snooping feature determines whether traffic sources are trusted or untrusted. The potential exists for a spurious DHCP server to respond to DHCPDISCOVER messages before the real server has time to respond. DHCP snooping allows switches on the network to trust the port a DHCP server is connected to and not trust the other ports. The DHCP snooping feature validates DHCP messages received from untrusted sources and filters out invalid messages as well as rate-limits DHCP traffic from trusted and untrusted sources. DHCP snooping feature builds and maintains a binding database, which contains information about untrusted hosts with leased IP addresses, and it utilizes the database to validate subsequent requests from untrusted hosts. Other security features, such as IP Source Guard and Dynamic Address Resolution Protocol (ARP) Inspection (DAI), also use information stored in the DHCP snooping binding database. Hence, it is imperative that the DHCP snooping feature is enabled on all user VLANs.
SRG-NET-000362-L2S-000026
1 Rule
The Arista MLS layer 2 switch must have IP Source Guard enabled on all user-facing or untrusted access switch ports.
Medium Severity
IP Source Guard (IPSG) provides source IP address filtering on a layer 2 port to prevent a malicious host from impersonating a legitimate host by assuming the legitimate host's IP address. The feature uses dynamic DHCP snooping and static IP source binding to match IP addresses to hosts on untrusted Layer 2 access ports. Initially, all IP traffic on the protected port is blocked except for DHCP packets. After a client receives an IP address from the DHCP server, or after static IP source binding is configured by the administrator, all traffic with that IP source address is permitted from that client. Traffic from other hosts is denied. This filtering limits a host's ability to attack the network by claiming a neighbor host's IP address.
SRG-NET-000362-L2S-000027
1 Rule
The Arista MLS layer 2 switch must have Dynamic Address Resolution Protocol (ARP) Inspection (DAI) enabled on all user VLANs.
Medium Severity
DAI intercepts Address Resolution Protocol (ARP) requests and verifies that each of these packets has a valid IP-to-MAC address binding before updating the local ARP cache and before forwarding the packet to the appropriate destination. Invalid ARP packets are dropped and logged. DAI determines the validity of an ARP packet based on valid IP-to-MAC address bindings stored in the DHCP snooping binding database. If the ARP packet is received on a trusted interface, the switch forwards the packet without any checks. On untrusted interfaces, the switch forwards the packet only if it is valid.
SRG-NET-000512-L2S-000002
1 Rule
The Arista MLS layer 2 switch must have IGMP or MLD Snooping configured on all VLANs.
Low Severity
IGMP and MLD snooping provides a way to constrain multicast traffic at Layer 2. By monitoring the IGMP or MLD membership reports sent by hosts within a VLAN, the snooping application can set up Layer 2 multicast forwarding tables to deliver specific multicast traffic only to interfaces connected to hosts interested in receiving the traffic, thereby significantly reducing the volume of multicast traffic that would otherwise flood the VLAN.
SRG-NET-000512-L2S-000003
1 Rule
The Arista MLS layer 2 Arista MLS switch must implement Rapid STP where VLANs span multiple switches with redundant links.
Medium Severity
Spanning Tree Protocol (STP) is implemented on bridges and switches to prevent layer 2 loops when a broadcast domain spans multiple bridges and switches and when redundant links are provisioned to provide high availability in case of link failures. Convergence time can be significantly reduced using Multiple Spanning-Tree (802.1s) instead of Rapid STP (802.1w) instead of STP (802.1d), resulting in improved availability. Multiple Spanning-Tree Protocol (MSTP) should be deployed by implementing either Rapid Per-VLAN-Spanning-Tree (Rapid-PVST) or Multiple Spanning-Tree MST, the latter scales topologies much better when there are many VLANs.
SRG-NET-000512-L2S-000004
1 Rule
The Arista MLS layer 2 switch must enable Unidirectional Link Detection (UDLD) to protect against one-way connections.
Medium Severity
In topologies where fiber optic interconnections are used, physical misconnections can occur that allow a link to appear to be up when there is a mismatched set of transmit/receive pairs. When such a physical misconfiguration occurs, protocols such as STP can cause network instability. UDLD is a layer 2 protocol that can detect these physical misconfigurations by verifying that traffic is flowing bidirectionally between neighbors. Ports with UDLD enabled periodically transmit packets to neighbor devices. If the packets are not echoed back within a specific time frame, the link is flagged as unidirectional and the interface is shut down.
SRG-NET-000512-L2S-000005
1 Rule
The Arista MLS layer 2 switch must have all trunk links enabled statically.
Medium Severity
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.
SRG-NET-000512-L2S-000007
1 Rule
The Arista MLS layer 2 switch must have all disabled switch ports assigned to an unused VLAN.
Medium Severity
It is possible that a disabled port that is assigned to a user or management VLAN becomes enabled by accident or by an attacker and as a result gains access to that VLAN as a member.
SRG-NET-000512-L2S-000008
1 Rule
The Arista MLS layer 2 switch must not have the default VLAN assigned to any host-facing switch ports.
Medium Severity
In a VLAN-based network, switches use the default VLAN (i.e., VLAN 1) for in-band management and to communicate with other networking devices using Spanning-Tree Protocol (STP), Dynamic Trunking Protocol (DTP), VLAN Trunking Protocol (VTP), and Port Aggregation Protocol (PAgP)—all untagged traffic. As a consequence, the default VLAN may unwisely span the entire network if not appropriately pruned. If its scope is large enough, the risk of compromise can increase significantly.
SRG-NET-000512-L2S-000009
1 Rule
The Arista MLS layer 2 switch must have the default VLAN pruned from all trunk ports that do not require it.
Medium Severity
The default VLAN (i.e., VLAN 1) is a special VLAN used for control plane traffic such as Spanning-Tree Protocol (STP), Dynamic Trunking Protocol (DTP), VLAN Trunking Protocol (VTP), and Port Aggregation Protocol (PAgP). VLAN 1 is enabled on all trunks and ports by default. With larger campus networks, care needs to be taken about the diameter of the STP domain for the default VLAN. Instability in one part of the network could affect the default VLAN, thereby influencing control-plane stability and therefore STP stability for all other VLANs.
SRG-NET-000512-L2S-000010
1 Rule
The Arista MLS layer 2 switch must not use the default VLAN for management traffic.
Medium Severity
Switches use the default VLAN (i.e., VLAN 1) for in-band management and to communicate with directly connected switches using Spanning-Tree Protocol (STP), Dynamic Trunking Protocol (DTP), VLAN Trunking Protocol (VTP), and Port Aggregation Protocol (PAgP)—all untagged traffic. As a consequence, the default VLAN may unwisely span the entire network if not appropriately pruned. If its scope is large enough, the risk of compromise can increase significantly.
SRG-NET-000512-L2S-000011
1 Rule
The Arista MLS layer 2 switch must have all user-facing or untrusted ports configured as access switch ports.
Medium Severity
Double encapsulation can be initiated by an attacker who has access to a switch port belonging to the native VLAN of the trunk port. Knowing the victim's MAC address and with the victim attached to a different switch belonging to the same trunk group, thereby requiring the trunk link and frame tagging, the malicious user can begin the attack by sending frames with two sets of tags. The outer tag that will have the attacker's VLAN ID (probably the well-known and omnipresent default VLAN) is stripped off by the switch, and the inner tag that will have the victim's VLAN ID is used by the switch as the next hop and sent out the trunk port.
SRG-NET-000512-L2S-000012
1 Rule
The Arista MLS layer 2 switch must have the native VLAN assigned to an ID other than the default VLAN for all 802.1q trunk links.
Medium Severity
VLAN hopping can be initiated by an attacker who has access to a switch port belonging to the same VLAN as the native VLAN of the trunk link connecting to another switch that the victim is connected to. If the attacker knows the victim’s MAC address, it can forge a frame with two 802.1q tags and a layer 2 header with the destination address of the victim. Since the frame will ingress the switch from a port belonging to its native VLAN, the trunk port connecting to the victim’s switch will simply remove the outer tag because native VLAN traffic is to be untagged. The switch will forward the frame on to the trunk link unaware of the inner tag with a VLAN ID of which the victim’s switch port is a member.
SRG-NET-000512-L2S-000013
1 Rule
The Arista MLS layer 2 switch must not have any switch ports assigned to the native VLAN.
Low Severity
Double encapsulation can be initiated by an attacker who has access to a switch port belonging to the native VLAN of the trunk port. Knowing the victim’s MAC address and with the victim attached to a different switch belonging to the same trunk group, thereby requiring the trunk link and frame tagging, the malicious user can begin the attack by sending frames with two sets of tags. The outer tag that will have the attacker’s VLAN ID (probably the well-known and omnipresent default VLAN) is stripped off by the switch, and the inner tag that will have the victim’s VLAN ID is used by the switch as the next hop and sent out the trunk port.
SRG-NET-000148-L2S-000015
1 Rule
The Arista MLS layer 2 switch must uniquely identify all network-connected endpoint devices before establishing any connection.
High Severity
Controlling LAN access via 802.1x authentication can assist in preventing a malicious user from connecting an unauthorized PC to a switch port to inject or receive data from the network without detection. Satisfies: SRG-NET-000148-L2S-000015, SRG-NET-000343-L2S-000016