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V-216692

CAT III (Low)

The Cisco BGP router 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.

Rule ID

SV-216692r1117236_rule

STIG

Cisco IOS XE Router RTR Security Technical Implementation Guide

Version

V3R5

CCIs

CCI-000032

Discussion

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 routers (ASBRs) must ensure updates received from eBGP peers list their AS number as the first AS in the AS_PATH attribute.

Check Content

Review the router configuration to verify the router 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 router 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 router 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

Configure the router to deny updates received from eBGP peers that do not list their AS number as the first AS in the AS_PATH attribute.

R1(config)#router bgp xx
R1(config-router)#bgp enforce-first-as