1. Presented By: Hanping Feng Configuring BGP With Cisco IOS Software (Part 1)

2. Outline q Cisco IOS software q Cisco IOS command modes q Basic BGP configuration tasks q Summary

3. Cisco IOS software p Overview m internetwork operating system m runs on the majority of Cisco networking equipment m provides intelligent network services: l security, multicast, load-balancing... p IOS User Interfaces m the command-line interface (CLI) m configuration tools l AutoInstall l the setup command facility l the ConfigMaker and FastStep configuration applications

4. Cisco IOS Command Modes p User EXEC mode p Privileged EXEC mode p Global configuration mode p Specific configuration modes p Configuration submodes p configuration subsubmodes p ROM Monitor Mode

5. Cisco IOS Command Modes Entering CLI User EXEC (Router>) Log in logout Privileged EXEC (Router#) enable disable Global configuration (Router(config)#) configure terminal exit/end/Ctrl+Z Interface configuration (Router(config-if)#) interface Router configuration (Router(config-router)#) router end/Ctrl+ZEnd/Ctrl+Z exit 

6. Basic BGP Configuration Tasks p Enabling BGP Routing p Configuring BGP Neighbors p Managing Routing Policy Changes p Verifying BGP Soft Reset p Configuring BGP Interactions with IGPs p Configuring BGP Administrative Weights p Disabling AS Path Comparison

7. Basic BGP Configuration Tasks p Configuring BGP Route Filtering by Neighbor p Configuring BGP Filtering Using Prefix Lists p Configuring BGP Path Filtering by Neighbor p Disabling Next-Hop Processing on BGP Updates p Configuring the BGP Version p Setting the Network Weight p Configuring the Multi Exit Discriminator Metric

8. Enabling BGP Routing Router(config)# router bgp autonomous-system Router(config-router)# Effect: Global configuration mode  Router configuration mode Number of the autonomous system to which the router belongs. Example: Router(config)# router bgp 200

9. Configuring BGP Neighbors Router(config-router)# neighbor {ip-address | peer-group-name} remote-as number ip-address Neighbor's IP address. peer-group-nameName of a BGP peer group. number Autonomous system to which the neighbor belongs.

10. Configuring BGP Neighbors !Router A router bgp 109 network 131.108.0.0 network 192.31.7.0 neighbor 131.108.200.1 remote-as 167 neighbor 131.108.234.2 remote-as 109 neighbor 150.136.64.19 remote-as 99

11. Managing Routing Policy Changes p BGP session must be reset to valid a policy change p reset methods: p hard reset p soft reset p outbound soft reset p inbound soft reset l configured inbound soft reset l dynamic inbound soft reset

12. Managing Routing Policy Changes Router# clear ip bgp {* | address | peer-group-name} [soft [in | out]] Router(config-router)# neighbor {ip-address | peer- group-name} soft-reconfiguration inbound Example: router bgp 100 neighbor 131.108.1.1 remote-as 200 neighbor 131.108.1.1 soft-reconfiguration inbound  clear ip bgp 131.108.1.1 soft in soft (Optional) Soft reset. in | out (Optional) Triggers inbound or outbound soft reset.

13. Verifying BGP Soft Reset p Check information about the BGP routing table Router# show ip bgp p Check information about BGP neighbors Router# show ip bgp neighbors [address]

14. Configuring BGP Interactions with IGPs p Synchronization is enabled by default. p In some cases, you do not need synchronization. p To disable synchronization: Router(config-router)# no synchronization

15. Configuring BGP Administrative Weights p a cisco-defined proprietary attribute p used in the path selection process p local to the router p to configure this attribute: Router(config-router)# neighbor {ip-address | peer-group-name} weight weight

16. Configuring BGP Administrative Weights (contd.) !Router C router bgp 300 neighbor 1.1.1.1 remote-as 100 neighbor 1.1.1.1 weight 2000 neighbor 2.2.2.2 remote-as 200 neighbor 2.2.2.2 weight 1000

17. Disabling AS Path Comparison p RFC1771 does not include AS-path in the path selection procedure p the Cisco implementation does by default p to ignore the as-path length when selecting a route: Router(config-router)# bgp bestpath as-path ignore

18. BGP Route Filtering p Three basic BGP configuration tasks involved: p Configuring BGP Route Filtering by Neighbor p Configuring BGP Filtering Using Prefix Lists p Configuring BGP Path Filtering by Neighbor

19. access-list-number: number of an access list. 1 to 99 or 1300 to 1999. deny: denies access if the address prefix is matched. permit: permits access if the address prefix is matched. address-prefix: the prefix to match. wildcard: wildcard bits. Place ones in the bit positions you want to ignore. p To apply a distribute list on a neighbor: neighbor {ip-address | peer-group-name} distribute- list access-list-number {in | out} Prefix Filtering  To define a distribute list: access-list access-list-number {deny | permit} address-prefix [wildcard] in: distribute list is applied to incoming advertisements. out: distribute list is applied to outgoing advertisements.

20. Prefix Filtering !Router C router bgp 300 network 170.10.0.0 neighbor 3.3.3.3 remote-as 200 neighbor 2.2.2.2 remote-as 100 neighbor 2.2.2.2 distribute-list 1 out ! access-list 1 deny 160.10.0.0 0.0.255.255 access-list 1 permit 0.0.0.0 255.255.255.255

21. AS_path Filtering p Router(config)# ip as-path access-list access- list-number {deny | permit} as-regular-expression p Router(config-router)# neighbor {ip-address | peer-group-name} filter-list access-list-number {in | out} as-regular-expression: a regular expression matching a specific sequence of ASes.

22. AS_path Filtering !Router C neighbor 3.3.3.3 remote-as 200 neighbor 2.2.2.2 remote-as 100 neighbor 2.2.2.2 filter-list 1 out ! ip as-path access-list 1 deny ^200$ ip as-path access-list 1 permit.*

23. Using A Prefix List  Router(config-router)# ip prefix-list list-name [seq seq- value] deny|permit network/len [ge ge-value] [le le-value]  Router(config-router)# neighbor {ip-address | peer- group-name} prefix-list prefix-listname {in | out} seq-value(Optional): Specifies the sequence number for the prefix list entry. network/len (Mandatory): The network number and length (in bits) of the network mask. ge-value(Optional): Specifies the lesser value of a range (the "from" portion of the range description). le-value(Optional): Specifies the greater value of a range (the "to" portion of the range description). Example: ip prefix-list abc deny 128.0.0.0/8 ge 23 le 24 ip prefix-list abc permit 0.0.0.0/0 neighbor 2.2.2.2 prxfix-list abc in

24. Disabling Next-Hop Processing on BGP Updates

25. !Router C router bgp 300 neighbor 170.10.20.1 remote-as 100 neighbor 170.10.20.1 next-hop-self Router(config-router)# neighbor {ip-address | peer- group-name} next-hop-self

26. Configuring the BGP Version  To prevent negotiation and force the BGP version used Router(config-router)# neighbor {ip-address | peer-group-name} version value p Example: neighbor 1.1.1.1 version 4

27. Setting the Network Weight p The weight attribute is 32768 for the paths that the router originates by default.  To set the absolute weight for a network: Router(config-router)# network address mask weight weight p Example: network 128.0.0.0 weight 2000

28. Configuring the Multi Exit Discriminator Metric Router(config-router)# default-metric number

29. Summary p CLI commands are enough to configure BGP. p Advanced BGP configuration tasks show the flexibility of BGP. p Route maps, aggregation, community, confederation, peer groups... p Thanks and to be continued...