Part 1: BGP Lab Setup
I.
Topology
II.
IP address Table
Lab2: BGP Basics
Figure 1 – BGP Lab Topology
Router
IP Address of s2/0
IP Address of s2/1
IP Address of e0/0
IP Address of e0/1
Loopback 0
R1
176.1.1.1/24
–
10.1.1.1/24
10.1.1.0/24 Net1
–
R2
176.1.2.2/24
–
10.1.1.2/24
10.1.3.2/24
R3
10.1.4.3/24
–
–
10.1.3.3/24
10.1.2.3/24
10.1.2.0/24 (Net2)
R4
176.1.1.4/24
–
–
176.1.3.4/24
176.1.3.0/24 Net3
–
R5
176.1.2.5/24
176.1.4.5/24
–
176.1.3.5/24
–
R6
10.1.4.6/24
176.1.4.6/24
–
–
192.168.1.6/24
192.168.1.0/24 (Net4)
III.
Configuration
1. Run EIGRP in AS100. EIGRP should carry all the routes in 10.1.0.0/16. 2. Setup BGP connections to the following router pairs.
R1-R2; R1-R3; R2-R3; R1-R4; R3-R6;
R4-R5; R5-R6;
router bgp
neighbor
Use additional neighbor ip-address next-hop-self command for the appropriate IBGP connections.
Q1: Which BGP connections require the next-hop-self configuration? Explain.
3. Use the network command in the routers to advertise networks 1, 2, 3 and 4 to their BGP peers. Do not use
redistribution.
router bgp
network
example:
router bgp 45
network 192.1.1.0 255.255.255.0
4. Disable link R5-R2.
5. Configure no synchronization in all the BGP processes.
router bgp
Part 2: Synchronization and IBGP Characteristics
Objective: To study the concept of synchronization and IBGP characteristics.
1. Use the original network setup with the following modifications:
• Disable link R6-R5
• Enable BGP synchronization in the BGP process running in AS100.
2. Use sh ip bgp command to show the BGP table. You will find that R1 learns Net4 from R3 and R3 learns Net3 from R1.
3. Check the routing tables of R1 and R3. You will find that the learned routes are not adopted in the routing tables.
4. Use no synchronization command to disable BGP synchronization. This will allow R1 to adopt Net4 and R3 to adopt Net3 in their respective routing tables.
5. Ping Net3 (e0/1 interface address of R4 or R5) from R3. The ping should be successful.
6. Disable the BGP connection (not the link!) between R1 and R2.
7. If you look up the routing table of R3, the table will still have the route to Net3.
8. Ping Net3 from R3.
Q2: The ping will not be successful. Explain why. Hint: Check the routing table of R2.
Design 1: If you configure the routers correctly, they will learn all the routes. Record your configuration. (note: the network address of the serial links that are not required to learned by all the routers)
Q1: Explain why the two routers (R1 and R3) do not adopt the routes learned from each other when the BGP synchronization is enabled.
Part 3: BGP Table
Objective: To examine and interpret the attribute contents in the BGP table. To study recursive lookup.
1. Use the original network setup:
Q1: Explain why we need to configure IGP in AS100 but not in AS200.
2. Use show ip pgp command to display the BGP table.
3. Study the BGP table in your router and determine the default values od the following BGP attributes: • Weight
• Local preference • Metric
4. Examine the BGP table of R1. You will find that some destinations may have more than one routes learned.
5. Examine the routing table of R1. Based on the routing table, determine the interface used by R1 to reach Net4.
Q3: Explain how would you use the recursive lookup to derive the nest-hop interface.
Part 4: Routing Updates
Objectives: To study the concepts of semi-dynamic and static routing updates. To investigate the characteristics of ORIGIN attribute.
1. Use the original network setup with the following modifications: Disable links R5-R6
2. Configure R1 to advertise network Net1 and Net2. Use the semi-dynamic routing update approach. 3. Verify your configuration by examining the routing tables of the routers in AS200 and AS300.
4. Disable R3’s connection to Net2.
Q1: Describe the events that will follow.
5. Repeat steps 2 and 4 by using the static routing update approach.
Q2: Again, describe the subsequent events after step 4.
6. Check the BGP table of R4, record the AS_PATH attribute and ORIGIN attribute of Net4.
7. Disconnect the BGP connection between R1 and R3, and redistribute BGP into EIGRP at R3. At this point, R1 learns Net4 through EIGRP alone. Consequently, it will not advertise Net4 to R4.
8. Configure R1 to advertise Net 4 to R4 using the network command. Record the new AS_PATH and ORIGIN attributes of Net4 in the BGP table of R4.
9. Disable the network configuration in the previous step. Instead, use the redistribute command to advertise Net4 to R4. Record the AS_PATH and ORIGIN attributes of Net4 in the BGP table of R4.
Q2: Interpret the AS_PATH attributes of the routers in the BGP table and explain how they are derived. Also explain how a route is preferred over other routes to the same destination.
Q3: Comment on the different results obtained in steps 6, 8, and 9.