prefix filtering netkit-lab-bgp-1

Transcription

1 prefix filtering netkit-lab-bgp-1

2 applying policies 1 announcement filtering send/accept an announcement only if some condition is verified commands: prefix-list used to filter prefixes filter-lists used to filter as numbers 2 announcement tuning attach to your announcement some information (attributes) that should be considered by the receiver commands: route-map

3 prefix filtering commands neighbor <neighbor-ip> prefix-list <p-list-name> in neighbor <neighbor-ip> prefix-list <p-list-name> out ip prefix-list <p-list-name> permit <network/mask> ip prefix-list <p-list-name> deny <network/mask>

4 prefix filtering: example zebra configuration file router bgp 1 network /24 network /24 neighbor remote-as 2 neighbor description Router 2 of AS2 neighbor prefix-list partialout out neighbor prefix-list partialin in! ip prefix-list partialout permit /24! ip prefix-list partialin deny /24 ip prefix-list partialin permit any only /24 is announced to neighbor all with the exception of /24 is accepted from

5 lab-bgp-3-prefix-filtering AS / /24 B C 1 eth2 1 eth1 1 eth / / /24 A 2 eth0 D 1 eth1 AS2 1 eth2 E

6 lab-bgp-3-prefix-filtering launch the script type prefix-filtering start check bgpd configuration file type more /etc/zebra/bgpd.conf check the routing table type route type telnet 0 zebra insert the password zebra type show ip route check bgp daemon log file type more /var/log/zebra/bgpd.log

7 lab-bgp-3-prefix-filtering check the bgpd cli (command line interface) type telnet 0 bgpd insert the password zebra type show ip bgp neighbors type show ip bgp terminate the script type prefix-filtering crash

8 attributes a bgp announce is a bag of attributes attributes may be well-known (mandatory) or optional attributes may be transitive or nontransitive transitive attributes are passed when received nontransitive attributes travel a single hop well-known attributes are always transitive

9 prefix attribute list the section of ip space announced as-path the sequence of traversed ases origin igp, egp, incomplete next-hop to be inserted in the routing table metric (multi-exit-discriminator) asking other as to prefer lower values of it local-pref asking ibgp peers to prefer lower values atomic aggregate aggregator weight cisco proprietary

10 attributes: prefix & as-path /24 as40 as / / / as / /24 as / as212 legenda: prefix as-path

11 bgp decision process highest priority lowest priority 1. largest weight (cisco proprietary) 2. largest local preference 3. locally originated 4. shortest as-path length 5. lowest origin 6. lowest multi-exit-discriminator 7. prefer ebgp over ibgp 8. lowest igp metric 9. lowest bgp router-id

12 attribute setting commands neighbor <neighbor-ip> route-map <r-map-name> in neighbor <neighbor-ip> route-map <r-map-name> out route-map <r-map-name> permit <seq-number> match <announce-property> set <attribute-setting>... route-map <r-map-name> deny <seq-number> match <announce-property> set <attribute-setting>...

13 attribute setting example zebra configuration file router bgp 100 network /24 neighbor remote-as 200 neighbor route-map myroutemap in! route-map myroutemap permit 10 match ip address myaccesslist set metric 5 set local-preference 25! route-map myroutemap permit 20 set metric 2! access-list myaccesslist permit /16

14 all match commands match as-path match community match clns match interface match ip address match ip next-hop match ip route-source match metric match route-type match tag

15 all set commands set as-path set clns set automatic-tag set community set interface set default interface set ip default next-hop set level set local-preference set metric set metric-type set next-hop set origin set tag set weight