The Cisco BGP switch must be configured to reject route advertisements from BGP peers that do not list their autonomous system (AS) number as the first AS in the AS_PATH attribute.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-221028	CISC-RT-000540	SV-221028r622190_rule		Low

Description
Verifying the path a route has traversed will ensure the IP core is not used as a transit network for unauthorized or possibly even internet traffic. All autonomous system boundary switches (ASBRs) must ensure updates received from eBGP peers list their AS number as the first AS in the AS_PATH attribute.

STIG	Date
Cisco IOS-XE Switch RTR Security Technical Implementation Guide	2022-09-13

Details

Check Text ( C-22743r408878_chk )

Review the switch configuration to verify the switch is configured to deny updates received from eBGP peers that do not list their AS number as the first AS in the AS_PATH attribute. By default, Cisco IOS enforces the first AS in the AS_PATH attribute for all route advertisements. Review the switch configuration to verify that the command no bgp enforce-first-as is not configured. router bgp xx no synchronization no bgp enforce-first-as If the switch is not configured to reject updates from peers that do not list their AS number as the first AS in the AS_PATH attribute, this is a finding.

Fix Text (F-22732r408879_fix)
Configure the switch to deny updates received from eBGP peers that do not list their AS number as the first AS in the AS_PATH attribute. SW1(config)#router bgp xx SW1(config-switch)#bgp enforce-first-as