1. © Synergon Informatika Rt., 1999 Chapter 12 Connecting Enterprises to an Internet Service Provider

2. 2 Objectives Upon completion of this chapter, you will be able to perform the following tasks: Determine when to use BGP to connect to an ISP Describe methods to connect to an ISP using static and default routes, and BGP

3. 3 BGP and ISP Connectivity Basics

4. 4 Internet Service Provider BGP Overview Autonomous System BGP used between autonomous systems (AS) ISP BGP configuration can be complex

5. 5 When Not to Use BGP ISP runs BGP Static A B Use a static route to provide connectivity Advertise default network via IGP Avoid BGP configuration by using default networks and static routes — Appropriate when the local policy is the same as the ISP policy

6. 6 AS 100 Policy Drives BGP Requirements A AS 400 F AS 200 C B AS 300 ED Static Route BGP Policy for AS 100: Always use AS 300 path to reach AS 400

7. 7 AS 100 Policy Drives BGP A AS 400 F AS 200 C B AS 300 ED BGP Downstream policy relies on upstream presence of BGP Router F must run BGP so that router A can implement policy

8. 8 BGP Sessions EBGP AS 1 Service Provider IBGP AS 2 BGP traffic is carried by TCP connections Two types of BGP session: External and internal

9. 9 BGP Operation IPBGP IGP Routing Protocol BGP Routing Protocol BGP routes can be redistributed into the IP routing table

10. 10 BGP Operation (cont.) IPBGP IGP Routing Protocol BGP Routing Protocol Redistributing IP into BGP requires: - The route to be known - The BGP network command

11. 11 Connecting to an ISP Using BGP and Alternatives

12. 12 ISP Connecting to an ISP Overview Enterprise Network Accomplished through static routes, default, or BGP

13. 13 Static Route Command Review ip route network mask {interface | ip-address} Router (config) #  Creates a static route  Can establish a “floating” route

14. 14 RIP Static Route Example ISP AS 100 19.0.0.0 AS 200 15.1.1.1 15.1.1.2 15.1.1.0 A S0 Service Provider Running BGP ip route 0.0.0.0 0.0.0.0 S0 ! router rip network 19.0.0.0 ip route 0.0.0.0 0.0.0.0 S0 ! router rip network 19.0.0.0

15. 15 OSPF Example ISP AS 100 19.0.0.0 AS 200 15.1.1.1 15.1.1.2 15.1.1.0 A S0 Service Provider Running BGP ip route 0.0.0.0 0.0.0.0 S0 ! router ospf 1 network 19.0.0.0 ip route 0.0.0.0 0.0.0.0 S0 ! router ospf 1 network 19.0.0.0 OSPF default configuration using a static route

16. 16 BGP Commands router bgp autonomous-system Router (config) # Enables the BGP routing protocol network network-number Router (config-router) # Allows BGP to advertise an IGP route if it is already in the IP table Does not activate the protocol on an interface

17. 17 BGP Commands (cont.) neighbor ip-address remote-as autonomous-system Router (config-router) # Actives a BGP clear ip bgp { * | address } Router # Resets BGP connections Use after changing BGP configuration

18. 18 BGP Configuration Example AS 100 19.0.0.0 AS 200 15.1.1.1 15.1.1.2 15.1.1.0 A S0 15.0.0.0 B Configuration for A route bgp 100 network 19.0.0.0 neighbor 15.1.1.2 remote-as 200 route bgp 100 network 19.0.0.0 neighbor 15.1.1.2 remote-as 200 Configuration for B route bgp 200 network 15.0.0.0 neighbor 15.1.1.1 remote-as 100 route bgp 200 network 15.0.0.0 neighbor 15.1.1.1 remote-as 100 Representative of most BGP configurations

19. 19 BGP show Commands show ip bgp Router # Displays the BGP routing table show ip bgp paths Router # Displays all paths in database show ip bgp summary Router # Displays status of all BGP connections

20. 20 Summary BGP is a protocol used to connect autonomous systems Static routes or default routes can be used if the autonomous system policy is consistent with ISP policy