Firewall Filter Support on Loopback Interface
A loopback interface is a gateway for all the control traffic that enters the Routing Engine of the router. If you want to monitor this control traffic, you must configure a firewall filter on the loopback interface (lo0).
Loopback firewall filters are only applied to packets sent to the Routing Engine for
further processing. Both inet and inet6 family filters are supported, and you can apply
a firewall filter in the ingress and egress directions on the lo0 interface. However,
only interface-specific instances of the firewall filter are
supported.
For standard firewall filter match conditions, see Match Conditions for IPv4 Traffic (ACX Series Routers).
The firewall filter on lo0 handles the following exception packets in ingress direction:
-
TTL exception packets
-
Multicast packets having 224.0.0.x as the destination IP address
-
Broadcast packets
-
IP option packets
Note:
Although policer actions can be attached to loopback filters in the ingress direction, the exact behavior depends on the CPU RX queue configurations. For example, rate limiting in ingress direction (through policer configuration) occurs after any CPU rate limiters.
The following is a sample configuration for attaching a firewall to the loopback interface:
[edit interfaces]
lo0 {
unit 0 {
family <inet | inet6> {
filter {
input f1;
}
}
}
}
family <inet | inet6>{
filter f1 {
interface-specific; >> Mandatory Field.
term t1 {
from {
protocol ospf;
}
then {
count c1;
discard;
}
}
term t2 {
then {
count c2;
accept;
}
}
}
}
A loopback firewall filter can also be configured to match commonly used protocols such as BGP, OSPF, SSH, Telnet, ICMP, SNMP etc. A sample configuration is as below:
set firewall family inet filter LoTest interface-specific set firewall family inet filter LoTest term tc1-ospfv2 from source-address 10.1.1.3/32 set firewall family inet filter LoTest term tc1-ospfv2 from protocol ospf set firewall family inet filter LoTest term tc1-ospfv2 then count LoCount set firewall family inet filter LoTest term tc1-ospfv2 then accept set firewall family inet filter LoTest term tc1-bgp4 from source-address 10.1.1.3/32 set firewall family inet filter LoTest term tc1-bgp4 from protocol tcp set firewall family inet filter LoTest term tc1-bgp4 from destination-port bgp set firewall family inet filter LoTest term tc1-bgp4 then count LoCount set firewall family inet filter LoTest term tc1-bgp4 then accept set firewall family inet filter LoTest term tc3-icmp from source-address 10.1.1.5/32 set firewall family inet filter LoTest term tc3-icmp from protocol icmp set firewall family inet filter LoTest term tc3-icmp from icmp-type 11 set firewall family inet filter LoTest term tc3-icmp from icmp-code 1 set firewall family inet filter LoTest term tc3-icmp then count LoCount set firewall family inet filter LoTest term tc3-icmp then accept set firewall family inet filter LoTest term tc5-tcpSyn from source-address 10.1.1.7/32 set firewall family inet filter LoTest term tc5-tcpSyn from protocol tcp set firewall family inet filter LoTest term tc5-tcpSyn from tcp-flags syn set firewall family inet filter LoTest term tc5-tcpSyn then policer LoPolicer set firewall family inet filter LoTest term tc5-tcpSyn then count LoCount set firewall family inet filter LoTest term tc5-tcpSyn then accept set firewall family inet filter LoTest term tc6-snmp from source-address 10.1.1.8/32 set firewall family inet filter LoTest term tc6-snmp from protocol udp set firewall family inet filter LoTest term tc6-snmp from destination-port snmp set firewall family inet filter LoTest term tc6-snmp then count LoCount set firewall family inet filter LoTest term tc6-snmp then accept set firewall family inet filter LoTest term tc6-ntp from source-address 10.1.1.8/32 set firewall family inet filter LoTest term tc6-ntp from protocol udp set firewall family inet filter LoTest term tc6-ntp from destination-port ntp set firewall family inet filter LoTest term tc6-ntp then count LoCount set firewall family inet filter LoTest term tc6-ntp then accept set firewall family inet filter LoTest term tc6-dns from source-address 10.1.1.8/32 set firewall family inet filter LoTest term tc6-dns from protocol udp set firewall family inet filter LoTest term tc6-dns from destination-port domain set firewall family inet filter LoTest term tc6-dns then count LoCount set firewall family inet filter LoTest term tc6-dns then accept set firewall family inet filter LoTest term tc8-ipOptions from source-address 10.1.1.10/32 set firewall family inet filter LoTest term tc8-ipOptions from ip-options router-alert set firewall family inet filter LoTest term tc8-ipOptions then count LoCount set firewall family inet filter LoTest term tc8-ipOptions then accept set firewall family inet filter LoTest term tc9-icmp from source-address 10.1.1.11/32 set firewall family inet filter LoTest term tc9-icmp from protocol icmp set firewall family inet filter LoTest term tc9-icmp from icmp-type 11 set firewall family inet filter LoTest term tc9-icmp from icmp-code 1 set firewall family inet filter LoTest term tc9-icmp then policer LoPolicer set firewall family inet filter LoTest term tc9-icmp then count LoCount set firewall family inet filter LoTest term tc9-icmp then accept set firewall family inet filter LoTest term tc12-ospfv2 from source-address 10.1.1.13/32 set firewall family inet filter LoTest term tc12-ospfv2 from protocol ospf set firewall family inet filter LoTest term tc12-ospfv2 then count LoCount set firewall family inet filter LoTest term tc12-ospfv2 then accept set firewall family inet filter LoTest term tc13-ssh from source-address 10.1.1.14/32 set firewall family inet filter LoTest term tc13-ssh from protocol tcp set firewall family inet filter LoTest term tc13-ssh from destination-port ssh set firewall family inet filter LoTest term tc13-ssh then count LoCount set firewall family inet filter LoTest term tc13-ssh then discard set firewall family inet filter LoTest term tc14-pl from source-address 10.1.1.15/32 set firewall family inet filter LoTest term tc14-pl from packet-length 4000-9000 set firewall family inet filter LoTest term tc14-pl from protocol ospf set firewall family inet filter LoTest term tc14-pl then count LoCount set firewall family inet filter LoTest term tc14-pl then accept set firewall family inet filter LoTest term tc16-pl from source-address 10.1.1.17/32 set firewall family inet filter LoTest term tc16-pl from fragment-flags more-fragments set firewall family inet filter LoTest term tc16-pl from protocol ospf set firewall family inet filter LoTest term tc16-pl then count LoCount set firewall family inet filter LoTest term tc16-pl then discard set firewall family inet filter LoTest term tc17-ssh from source-address 10.1.1.18/32 set firewall family inet filter LoTest term tc17-ssh from destination-address 10.216.66.30/32 set firewall family inet filter LoTest term tc17-ssh from protocol tcp set firewall family inet filter LoTest term tc17-ssh from destination-port ssh set firewall family inet filter LoTest term tc17-ssh then count LoCount set firewall family inet filter LoTest term tc17-ssh then accept set firewall family inet filter LoTest term all then accept set firewall family inet6 filter LoTest6 interface-specific set firewall family inet6 filter LoTest6 term tc2-ospfv3 from source-address 2001:db8:4136:e378:8000:63bf:3fff:fdd2 set firewall family inet6 filter LoTest6 term tc2-ospfv3 from next-header ospf set firewall family inet6 filter LoTest6 term tc2-ospfv3 then count LoCount6 set firewall family inet6 filter LoTest6 term tc2-ospfv3 then accept set firewall family inet6 filter LoTest6 term tc2-bgp4plus from source-address 2001:db8:4136:e378:8000:63bf:3fff:fdd2 set firewall family inet6 filter LoTest6 term tc2-bgp4plus from next-header tcp set firewall family inet6 filter LoTest6 term tc2-bgp4plus from destination-port bgp set firewall family inet6 filter LoTest6 term tc2-bgp4plus then count LoCount6 set firewall family inet6 filter LoTest6 term tc2-bgp4plus then accept set firewall family inet6 filter LoTest6 term tc4-icmpv6 from source-address 2001:db8:4136:e378:8000:63bf:3fff:fdd3 set firewall family inet6 filter LoTest6 term tc4-icmpv6 from next-header icmp6 set firewall family inet6 filter LoTest6 term tc4-icmpv6 from icmp-type 1 set firewall family inet6 filter LoTest6 term tc4-icmpv6 from icmp-code 0 set firewall family inet6 filter LoTest6 term tc4-icmpv6 then count LoCount6 set firewall family inet6 filter LoTest6 term tc4-icmpv6 then accept set firewall family inet6 filter LoTest6 term tc7-snmp from next-header udp set firewall family inet6 filter LoTest6 term tc7-snmp from destination-port snmp set firewall family inet6 filter LoTest6 term tc7-snmp then count LoCount6 set firewall family inet6 filter LoTest6 term tc7-snmp then accept set firewall family inet6 filter LoTest6 term tc7-ntp from next-header udp set firewall family inet6 filter LoTest6 term tc7-ntp from destination-port ntp set firewall family inet6 filter LoTest6 term tc7-ntp then count LoCount6 set firewall family inet6 filter LoTest6 term tc7-ntp then accept set firewall family inet6 filter LoTest6 term tc7-dns from next-header udp set firewall family inet6 filter LoTest6 term tc7-dns from destination-port domain set firewall family inet6 filter LoTest6 term tc7-dns then count LoCount6 set firewall family inet6 filter LoTest6 term tc7-dns then accept set firewall family inet6 filter LoTest6 term tc10-icmp from source-address 2001:db8:4136:e378:8000:63bf:3fff:fdd4 set firewall family inet6 filter LoTest6 term tc10-icmp from next-header icmp6 set firewall family inet6 filter LoTest6 term tc10-icmp from icmp-type 1 set firewall family inet6 filter LoTest6 term tc10-icmp from icmp-code 0 set firewall family inet6 filter LoTest6 term tc10-icmp then policer LoPolicer set firewall family inet6 filter LoTest6 term tc10-icmp then count LoCount6 set firewall family inet6 filter LoTest6 term tc10-icmp then accept set firewall family inet6 filter LoTest6 term all then accept set firewall policer LoPolicer if-exceeding bandwidth-limit 22k set firewall policer LoPolicer if-exceeding burst-size-limit 20k set firewall policer LoPolicer then discard