I had a brief discussion on Twitter about filtering between RIB and FIB tables in Junos where participants were not sure if it was possible at all.
It appears it is possible. Here’s a very quick test with a single router, one interface and a single static route.
interfaces {
ge-0/0/0 {
unit 0 {
family inet {
address 192.168.12.1/24;
}
}
}
}
routing-options {
static {
route 10.0.0.0/24 next-hop 192.168.12.2;
}
}
Let’s take a look at the forwarding table before we try the filtering:
markom@J1# run show route forwarding-table family inet
Routing table: default.inet
Internet:
Destination Type RtRef Next hop Type Index NhRef Netif
default perm 0 rjct 36
10.0.0.0/32 perm 0 dscd 34 1
10.0.0.0/24 user 0 192.168.12.2 hold 544 3 ge-0/0/0.0
192.168.12.0/24 intf 0 rslv 543 1 ge-0/0/0.0
192.168.12.0/32 dest 0 192.168.12.0 recv 541 1 ge-0/0/0.0
192.168.12.1/32 intf 0 192.168.12.1 locl 542 2
192.168.12.1/32 dest 0 192.168.12.1 locl 542 2
192.168.12.2/32 dest 0 192.168.12.2 hold 544 3 ge-0/0/0.0
192.168.12.255/32 dest 0 192.168.12.255 bcst 540 1 ge-0/0/0.0
224.0.0.0/4 perm 0 mdsc 35 1
224.0.0.1/32 perm 0 224.0.0.1 mcst 31 1
255.255.255.255/32 perm 0 bcst 32 1
Now, let’s add the filter into the configuration. The purpose here is to prevent the 10.0.0.0/24 route to make it into the forwarding table.
policy-options {
policy-statement FILTER {
term 10 {
from {
route-filter 10.0.0.0/24 exact;
}
then reject;
}
term 20 {
then accept;
}
}
}
routing-options {
forwarding-table {
export FILTER;
}
}
What’s the state of the forwarding table now?
markom@J1# run show route forwarding-table family inet
Routing table: default.inet
Internet:
Destination Type RtRef Next hop Type Index NhRef Netif
default perm 0 rjct 36
10.0.0.0/32 perm 0 dscd 34 1
192.168.12.0/24 intf 0 rslv 543 1 ge-0/0/0.0
192.168.12.0/32 dest 0 192.168.12.0 recv 541 1 ge-0/0/0.0
192.168.12.1/32 intf 0 192.168.12.1 locl 542 2
192.168.12.1/32 dest 0 192.168.12.1 locl 542 2
192.168.12.2/32 dest 0 192.168.12.2 hold 544 2 ge-0/0/0.0
192.168.12.255/32 dest 0 192.168.12.255 bcst 540 1 ge-0/0/0.0
224.0.0.0/4 perm 0 mdsc 35 1
224.0.0.1/32 perm 0 224.0.0.1 mcst 31 1
255.255.255.255/32 perm 0 bcst 32 1
It appears that filtering is working, as expected. Before I end, let’s make sure the route is actually still in the RIB.
markom@J1# run show route 10.0.0.0/24 detail
inet.0: 3 destinations, 3 routes (3 active, 0 holddown, 0 hidden)
10.0.0.0/24 (1 entry, 0 announced)
*Static Preference: 5
Next hop type: Router
Address: 0x8f9a130
Next-hop reference count: 2
Next hop: 192.168.12.2 via ge-0/0/0.0, selected
State:
Age: 59
Task: RT
AS path: I
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