The NSX-T Tier-0 Gateway must be configured to have Internet Control Message Protocol (ICMP) redirects disabled on all external interfaces.

Severity	Group ID	Group Title	Version	Rule ID	Date	STIG Version
medium	V-251755	SRG-NET-000362-RTR-000115	T0RT-3X-000066	SV-251755r856696_rule	2022-09-01	1

Description
The ICMP supports IP traffic by relaying information about paths, routes, and network conditions. Routers automatically send ICMP messages under a wide variety of conditions. Redirect ICMP messages are commonly used by attackers for network mapping and diagnosis.

ℹ️ Check
If the Tier-0 Gateway is deployed in an Active/Active HA mode, this is Not Applicable. From the NSX-T Manager web interface, go to Security >> Gateway Firewall >> Gateway Specific Rules, and choose each Tier-0 Gateway in the drop-down. Review each Tier-0 Gateway Firewalls rules to verify one exists to drop ICMP redirects. If a rule does not exist to drop ICMP redirects, this is a finding.

✔️ Fix
To configure a shared rule to drop ICMP unreachable messages do the following: From the NSX-T Manager web interface, go to Security >> Gateway Firewall >> All Shared Rules. Click "Add Rule" (Add a policy first if needed), under services select "ICMP Redirect", and then click "Apply". Enable logging, under the "Applied To" field select the target Tier-0 Gateways, and then click "Publish" to enforce the new rule. Note: A rule can also be created under Gateway Specific Rules to meet this requirement.

✔️ Fix

To configure a shared rule to drop ICMP unreachable messages do the following: From the NSX-T Manager web interface, go to Security >> Gateway Firewall >> All Shared Rules. Click "Add Rule" (Add a policy first if needed), under services select "ICMP Redirect", and then click "Apply". Enable logging, under the "Applied To" field select the target Tier-0 Gateways, and then click "Publish" to enforce the new rule. Note: A rule can also be created under Gateway Specific Rules to meet this requirement.