The Cisco switch must manage excess bandwidth to limit the effects of packet flooding types of denial of service (DoS) attacks.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-220651	CISC-L2-000040	SV-220651r539671_rule		Medium

Description

Denial of service is a condition when a resource is not available for legitimate users. Packet flooding 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).

STIG	Date
Cisco IOS XE Switch L2S Security Technical Implementation Guide	2021-09-09

Details

Check Text ( C-22366r507501_chk )

Step 1: Verify that the class-maps are configured to match on DSCP values as shown in the configuration example below: class-map match-all C2_VOICE match ip dscp af47 class-map match-all VOICE match ip dscp ef class-map match-all VIDEO match ip dscp af41 class-map match-all PREFERRED_DATA match ip dscp af33 Step 2: Verify that the policy map reserves the bandwidth for each traffic type as shown in the following example: policy-map QOS_POLICY_SWITCHPORT class C2_VOICE priority level 1 10 class VOICE priority level 2 15 class VIDEO bandwidth percent 25 class PREFERRED_DATA bandwidth percent 25 class class-default bandwidth percent 25 verone interface GigabitEthernet1/1 switchport trunk allowed vlan 100,110,200 switchport mode trunk service-policy output QOS_POLICY_SWITCHPORT ! interface GigabitEthernet1/2 switchport access vlan 100 switchport mode access switchport voice vlan 200 trust device cisco-phone service-policy output QOS_POLICY_SWITCHPORT ! interface GigabitEthernet1/2 switchport access vlan 110 switchport mode access switchport voice vlan 200 trust device cisco-phone service-policy output QOS_POLICY_SWITCHPORT If QoS has not been enabled, this is a finding.

Fix Text (F-22355r507502_fix)

Step 1: Configure class-maps to match on DSCP values as shown in the configuration example below: SW1(config-cmap)#class-map match-all C2_VOICE SW1(config-cmap)# match ip dscp 47 SW1(config-cmap)#class-map match-all VOICE SW1(config-cmap)# match ip dscp ef SW1(config-cmap)#class-map match-all VIDEO SW1(config-cmap)# match ip dscp af41 SW1(config)#class-map match-all PREFERRED_DATA SW1(config-cmap)# match ip dscp af33 SW1(config-cmap)#exit Step 2: Configure a policy map to be applied to the core-layer-facing interface that reserves the bandwidth for each traffic type as shown in the example below: SW1(config)#policy-map QOS_POLICY_SWITCHPORT SW1(config-pmap-c)#class C2_VOICE SW1(config-pmap-c)# priority level 1 10 SW1(config-pmap-c)#class VOICE SW1(config-pmap-c)# priority level 2 15 SW1(config-pmap-c)#class VIDEO SW1(config-pmap-c)#bandwidth percent 25 SW1(config-pmap-c)#class PREFERRED_DATA SW1(config-pmap-c)#bandwidth percent 25 SW1(config-pmap-c)#class class-default SW1(config-pmap-c)#bandwidth percent 25 SW1(config-pmap-c)#exit SW1(config-pmap)#exit Step 3: Apply the output service policy to the core-layer-facing interface as shown in the configuration example below: SW1(config)#int g1/1 SW1(config-if)#service-policy output QOS_POLICY_SWITCHPORT SW1(config-if)#exit SW1(config)#int g1/2 SW1(config-if)#service-policy output QOS_POLICY_SWITCHPORT SW1(config-if)#exit SW1(config)#int g1/3 SW1(config-if)#service-policy output QOS_POLICY_SWITCHPORT SW1(config-if)#end.