The Cisco PE switch must be configured with Unicast Reverse Path Forwarding (uRPF) loose mode enabled on all CE-facing interfaces.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-220456	CISC-RT-000740	SV-220456r622190_rule		Medium

Description
The uRPF feature is a defense against spoofing and denial-of-service (DoS) attacks by verifying if the source address of any ingress packet is reachable. To mitigate attacks that rely on forged source addresses, all provider edge switches must enable uRPF loose mode to guarantee that all packets received from a CE switch contain source addresses that are in the route table.

STIG	Date
Cisco IOS Switch RTR Security Technical Implementation Guide	2021-03-19

Details

Check Text ( C-22171r508446_chk )
Review the switch configuration to determine if uRPF loose mode is enabled on all CE-facing interfaces. interface GigabitEthernet0/2 no switchport ip address x.1.12.2 255.255.255.252 ip access-group BLOCK_TO_CORE in ip verify unicast source reachable-via any If uRPF loose mode is not enabled on all CE-facing interfaces, this is a finding.

Fix Text (F-22160r508447_fix)
Configure uRPF loose mode on all CE-facing interfaces as shown in the example below: SW2(config)#int SW1(config)#int g0/2 SW2(config-if)#ip verify unicast source reachable-via any SW2(config-if)#end