The Dell OS10 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.

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.

By default, the Dell OS10 Router rejects route advertisements from BGP peers that do not list their AS number as the first AS in the AS_PATH attribute. Verify that this behavior has not been disable by reviewing the running-configuration of BGP:

OS10# show running-configuration bgp ! router bgp 100 no enforce-first-as … !

Verify that "no enforce-first-as" has not been configured for BGP. If "no enforce-first-as" has been configured, this is a finding.

Configure the BGP router to reject route advertisements from BGP peers that do not list their AS number as the first AS in the AS_PATH attribute.

OS10# configure terminal OS10 (config)# router bgp 100 OS10(config-router-bgp-100)# enforce-first-as OS10(config-router-bgp-100)# end