This requirement is not applicable for the DODIN Backbone. Review the configuration of each router interface connecting to an alternate gateway. Verify each permit statement of the ingress filter only permits packets with destination addresses of the site's NIPRNet address space or a destination address belonging to the address block assigned by the alternate gateway network service provider. Verify each permit statement "from" stanza (filter match conditions) references either the "destination-address" or "destination-prefix-list" directive. Using prefix lists makes management easier because managing interior addresses must only be configured in one location (the prefix-list) vice many locations (each permitting filter term). For example: [edit policy-options] prefix-list inside_addresses-ipv4 { <IPv4 subnet / mask>; } prefix-list inside_addresses-ipv6 { <IPv6 subnet / prefix>; } [edit firewall] family inet { filter inbound-ipv4 { <deny terms>; permit-term1 { from { <match conditions>; destination-prefix-list inside_addresses-ipv4; } then accept; } <additional permit terms with a destination address definition> } } family inet6 { filter inbound-ipv6 { <deny terms>; permit-term1 { from { <match conditions>; destination-prefix-list inside_addresses-ipv6; } then accept; } <additional permit terms with a destination address definition> } } Verify the filter is applied inbound on exterior-facing interfaces. For example: [edit interfaces] <interface name> { unit <number> { family inet { filter { input inbound-ipv4; } address <IPv4 address / mask>; } family inet6 { filter { input inbound-ipv6; } address <IPv6 address / prefix>; } } } Note: Some Juniper devices support both monolithic filters and filter lists. Filter lists separate each term, or set of terms, into a separate filter that is applied sequentially to an interface. If using filter lists, the keywords "input" or "output" change to "input-list" or "output-list". Verify the final list item is a deny-all filter. If the ingress filter permits packets with addresses other than those specified, such as destination addresses of the site's NIPRNet address space or a destination address belonging to the address block assigned by the alternate gateway network service provider, this is a finding.