The Cisco ACI must be configured to use its loopback address as the source address for internal Border Gateway Protocol (iBGP) peering sessions.

Severity	Group ID	Group Title	Version	Rule ID	Date	STIG Version
low	V-272098	SRG-NET-000512-RTR-000001	CACI-RT-000038	SV-272098r1168415_rule	2025-12-11	1

Description
Using a loopback address as the source address offers a multitude of uses for security, access, management, and scalability of the BGP routers. It is easier to construct appropriate ingress filters for router management plane traffic destined to the network management subnet since the source addresses will be from the range used for loopback interfaces instead of a larger range of addresses used for physical interfaces. Log information recorded by authentication and syslog servers will record the router's loopback address instead of the numerous physical interface addresses. When the loopback address is used as the source for external BGP (eBGP) peering, the BGP session will be harder to hijack since the source address to be used is not known globally, making it more difficult for a hacker to spoof an eBGP neighbor. By using traceroute, a hacker can easily determine the addresses for an eBGP speaker when the IP address of an external interface is used as the source address. The routers within the iBGP domain should also use loopback addresses as the source address when establishing BGP sessions.

Description

Using a loopback address as the source address offers a multitude of uses for security, access, management, and scalability of the BGP routers. It is easier to construct appropriate ingress filters for router management plane traffic destined to the network management subnet since the source addresses will be from the range used for loopback interfaces instead of a larger range of addresses used for physical interfaces. Log information recorded by authentication and syslog servers will record the router's loopback address instead of the numerous physical interface addresses. When the loopback address is used as the source for external BGP (eBGP) peering, the BGP session will be harder to hijack since the source address to be used is not known globally, making it more difficult for a hacker to spoof an eBGP neighbor. By using traceroute, a hacker can easily determine the addresses for an eBGP speaker when the IP address of an external interface is used as the source address. The routers within the iBGP domain should also use loopback addresses as the source address when establishing BGP sessions.

ℹ️ Check
Review the switch configuration to verify a loopback address has been configured. Tenants >> {{your_Tenant}} >> L3Out >> {{your_l3out}} >> Logical Node Profiles >> {{your_Logical_node_Profile}} >> Policy >> BGP Peer Connectivity add your loopback If the switch does not use its loopback address as the source address for all iBGP sessions, this is a finding.

✔️ Fix
Configure BGP for the relevant L3Out to use the switch's loopback address as the source address for all iBGP peering. This configures the switch to use the loopback interface as the source IP for all BGP updates sent to the specified peer. - Navigate to Tenants >> {{your_Tenant}} >> Networking >> L3Out >> {{your_l3out}} >> Logical Node Profiles >> {{your_Logical_node_Profile}} >> Policy >> Node. - Double click the Node(Leaf) and look for the option to select "use Router ID as loopback" or set the loopback address to which to build the BGP connection and unselect "use router ID as Loopback". After setting the loopback address, navigate to Tenants >> {{your_Tenant}} >> L3Out >> {{your_l3out}} >> Logical Node Profiles >> {{your_Logical_node_Profile}} >> Policy >> BGP Peer Connectivity. Add the loopback.

✔️ Fix

Configure BGP for the relevant L3Out to use the switch's loopback address as the source address for all iBGP peering. This configures the switch to use the loopback interface as the source IP for all BGP updates sent to the specified peer. - Navigate to Tenants >> {{your_Tenant}} >> Networking >> L3Out >> {{your_l3out}} >> Logical Node Profiles >> {{your_Logical_node_Profile}} >> Policy >> Node. - Double click the Node(Leaf) and look for the option to select "use Router ID as loopback" or set the loopback address to which to build the BGP connection and unselect "use router ID as Loopback". After setting the loopback address, navigate to Tenants >> {{your_Tenant}} >> L3Out >> {{your_l3out}} >> Logical Node Profiles >> {{your_Logical_node_Profile}} >> Policy >> BGP Peer Connectivity. Add the loopback.