IP Prefix List Example
Prefix lists also can be used and, indeed, should be used. The preceding example was rewritten using the ip prefix-list commands available in Cisco IOS Software versions 11.1CC and 12.0 and later software releases. This makes the configuration more readable, if not more intuitive. Again, remember to check the root nameserver networks for any changes before implementing these. It is also worth checking the BGP routing table to ensure that these networks still are announced with the following prefix lengths:
router bgp 652 bgp dampening
ip prefix-list ip prefix-list !
ip prefix-list ip prefix-list !
ip prefix-list prefixes ip prefix-list !
ip prefix-list ip prefix-list ip prefix-list ip prefix-list ip prefix-list ip prefix-list ip prefix-list ip prefix-list ip prefix-list ip prefix-list ip prefix-list ip prefix-list ip prefix-list !
ip prefix-list ip prefix-list ip prefix-list ip prefix-list ip prefix-list ip prefix-list ip prefix-list ip prefix-list ip prefix-list ip prefix-list
route-map RIPE229-flap-damp my-nets description Networks we don't suppress my-nets seq 5 permit 169.223.0.0/16
suppress22 description Dampening of /22 and /23 prefixes suppress22 seq 5 permit 0.0.0.0/0 ge 22 le 23
suppress24 description Dampening of /24 and longer suppress24 seq 5 permit 0.0.0.0/0 ge 24
rootns description Root-nameserver networks rootns permit 198.41.0.0/24 ! A & J
rootns permit 128.9.0.0/16 ! B
rootns permit 192.33.4.0/24 ! C
rootns permit 128.8.0.0/16 ! D
rootns permit 192.203.230.0/24 ! E
rootns permit 192.5.4.0/23 ! F
rootns permit 192.112.36.0/24 ! G
rootns permit 128.63.0.0/16 ! H
rootns permit 192.36.148.0/24 ! I
rootns permit 193.0.14.0/24 ! K
rootns permit 198.32.64.0/24 ! L
rootns permit 202.12.27.0/24 ! M
gtldns description Global Top Level Domain Servers gtldns permit 192.5.6.0/24 ! A
gtldns permit 192.33.14.0/24 ! B
gtldns permit 192.26.92.0/24 ! C
gtldns permit 192.31.80.0/24 ! D
gtldns permit 192.12.94.0/24 ! E
gtldns permit 192.35.51.0/24 ! F
gtldns permit 192.42.93.0/24 ! G
gtldns permit 192.54.112.0/24 ! H
gtldns permit 192.36.144.0/24 ! I
ip prefix-list gtldns permit 210.132.96.0/19 ! J ip prefix-list gtldns permit 213.177.192.0/21 ! K ip prefix-list gtldns permit 192.41.162.0/24 ! L
ip prefix-list gtldns permit 202.153.112.0/20 ! M !
route-map RIPE229-flap-damp deny 10 match ip address prefix-list my-nets
route-map RIPE229-flap-damp deny 20 match ip address prefix-list rootns
route-map RIPE229-flap-damp deny 30 match ip address prefix-list gtldns
route-map RIPE229-flap-damp permit 40 match ip address prefix-list suppress24 set dampening 30 820 3000 60
route-map RIPE229-flap-damp permit 50 match ip address prefix-list suppress22 set dampening 15 750 3000 45
route-map RIPE229-flap-damp permit 60 set dampening 10 1500 3000 30
Continue reading here: What Other ISPs Are Doing
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