Title

The BGP Cisco ACI 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. (Cat III impact)

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. Cisco ACI BGP usually enforces the "first-as" rule by default.

Check Content

By default, Cisco ACI enforces the first AS in the AS_PATH attribute for all route advertisements. Review the configuration to verify the default BGP configuration on the ACI fabric is does not explicitly state: no enforce first-as If the device 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 device to deny updates received from eBGP peers that do not list their AS number as the first AS in the AS_PATH attribute. Remove the configuration item "no enforce first-as".

Additional Identifiers

Rule ID: SV-272064r1064467_rule

Vulnerability ID: V-272064

Group Title: SRG-NET-000018-RTR-000006

Expert Comments

CCIs tied to check.

Controls tied to check. These are derived from the CCIs shown above.