Routing Filter is a main tool to control and modifying
route information, whether you will discard or accept the routeing information.
Not only that you can do a lot of action like change distance, set community,
even you will used for BGP attribute path selection (weight, prepend, local preff, etc). Now we will try to
configure prefix filtering.
We are going to filter prefix 10.10.10.10/32 which
advertised from Internet Router. We are will discarded the prefix from R2. See
before and after config :
Before :
[admin@R2] > ip route print
Flags: X - disabled, A - active, D - dynamic, C -
connect, S - static, r - rip, b - bgp, o - ospf, m - mme,
B - blackhole, U - unreachable, P - prohibit
# DST-ADDRESS PREF-SRC GATEWAY DISTANCE
0 ADb 1.1.1.1/32 23.23.23.1 20
1 ADC 2.2.2.2/32 2.2.2.2 lo1 0
2 ADb 8.8.4.4/32 23.23.23.1 20
3 ADb 8.8.8.8/32 23.23.23.1 20
4 ADb
10.10.10.10/32 23.23.23.1 2
5 ADC 23.23.23.0/30 23.23.23.2 ether1 0
Filtering config :
[admin@R2] > routing
filter add chain=trafic-in prefix=10.10.10.10/32 action=discard
[admin@R2] > routing
bgp peer set 0 in-filter=trafic-in
After :
[admin@R2] > ip route print
Flags: X - disabled, A - active, D - dynamic, C -
connect, S - static, r - rip, b - bgp, o - ospf, m - mme,
B - blackhole, U - unreachable, P - prohibit
# DST-ADDRESS PREF-SRC GATEWAY DISTANCE
0 ADb 1.1.1.1/32 23.23.23.1 20
1 ADC 2.2.2.2/32 2.2.2.2 lo1 0
2 ADb 8.8.4.4/32 23.23.23.1 20
3 ADb 8.8.8.8/32 23.23.23.1 20
4 ADC 23.23.23.0/30 23.23.23.2 ether1 0
See after filter is applied on R3 prefix 10.10.10.10/32
is gone!
Out Filter
We are going to filter prefix 1.1.1.1/32 from R1 which
has advertised to public. And we are going to discard the prefix now!
See the routing table below before discarding the prefix
will shown on another router for example we are going to see R2’s routing
table!
[admin@R2] > ip route print
Flags: X - disabled, A - active, D - dynamic, C -
connect, S - static, r - rip, b - bgp, o - ospf, m - mme,
B - blackhole, U - unreachable, P - prohibit
# DST-ADDRESS PREF-SRC GATEWAY DISTANCE
0 ADb 1.1.1.1/32 23.23.23.1 20
1 ADC 2.2.2.2/32 2.2.2.2 lo1 0
2 ADb 8.8.4.4/32 23.23.23.1 20
3 ADb 8.8.8.8/32 23.23.23.1 20
4 ADC 23.23.23.0/30 23.23.23.2 ether1 0
[admin@R1] > routing filter add chain=trafic-out
prefix=1.1.1.1/32 action=discard
[admin@R1] > routing bgp peer set 0
out-filter=trafic-out
After applying out filter the prefix 1.1.1.1/32 is gone!
[admin@R2] > ip route print
Flags: X - disabled, A - active, D - dynamic, C -
connect, S - static, r - rip, b - bgp, o - ospf, m - mme,
B - blackhole, U - unreachable, P - prohibit
# DST-ADDRESS PREF-SRC GATEWAY DISTANCE
1 ADC 2.2.2.2/32 2.2.2.2 lo1 0
2 ADb 8.8.4.4/32 23.23.23.1 20
3 ADb 8.8.8.8/32 23.23.23.1 20
4 ADC 23.23.23.0/30 23.23.23.2 ether1 0
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