2. DECENTRALISING UNDER PRESSURE: THE SPANISH
2.4 Framing the debate, constraining the Court (part 1)
Technologies Covered
Weight
Local Preference
As-path prepending
Origin
MED
Always compare MED
AS-path ignore
Maximum AS Limit
Overview
The focus of this lab is BGP Attribute manipulations. To successfully finish this scenario you have to know what is the purpose of Weight, Local Preference, AS Path, Origin and MED attributes, and how to configure/modify them.
Estimated Time to Complete: 4 hours
iPexpert’s Recommended Reading Material
BGP Best Path Selection Algorithm:
http://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/13753-25.html
Connecting to a Service Provider using External BGP:
http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_bgp/configuration/15-mt/irg-15-mt-book/connecting_to_a_service_provider_using_external_bgp.html
iPexpert’s Recommended Video Training
iPexpert’s Video on Demand training library contains a wealth of videos pertaining to the CCIE Routing & Switching lab exam. We recommend watching the following learning videos that cover the topics seen in this lab scenario.
Video Title: BGP Route Propagation Control
Video Title: BGP Filtering & Manipulations
Video Title: BGP Attributes and Best-path Selection Process
Topology Details
Logically connect and configure your network as displayed in the drawing below. You may also refer to the diagram located within your configuration files for topology information.
The topology used in the lab will be the following:
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Diagram 20.1: BGP Topology
Lab 20 Setup
This lab is intended to be used with online rack access. Connect to the terminal server for the online rack, and complete the configuration tasks as detailed below.
Configuration Tasks
1. Configure an iBGP peering between R4 and R7 in AS 65001. Make sure that the 10.1.46.0/24 network and that the network 10.1.78.0/24 is carried in the BGP updates with an origin of i.
2. Configure an eBGP peering between R4 in AS 65001 and R6 in AS 65002.
3. Configure an eBGP peering between R6 in AS 65002 and R8 in AS 8.
NOTE
Load the initial configuration files before starting to work on the tasks.
5. The loopback0 of R4 should be present in the BGP database with an origin attribute of incomplete. The loopback0 of R7 should be present in the BGP database with an origin attribute of internal.
6. On R8, manipulate the weight attribute so that the route to 10.1.4.4/32 is pointing towards R6.
Use a prefix-list called WEIGHT_PL and a route-map called WEIGHT_RM.
7. The loopback0 of R6 should be present in the BGP database with an origin attribute of incomplete.
8. In order to reach the 10.1.6.6/32 loopback, routers in AS 65001 should route the traffic over R8 through AS 8. Change the configuration on R7 and use a route-map called LOCALPRF_RM. You don’t have to test connectivity in this task.
9. The loopback0 of R8 should be present in the BGP database with an origin attribute of IGP.
10. Configure R8 so that the traffic originated on R6 is going through AS 65001 to reach the network 10.1.8.8/32. On R6, 10.1.8.8 route via R8 should have the following AS-path attribute: 8 8 8 8 i.
Use a prefix-list called PREPEND_PL and a route-map called PREPEND_RM.
11. Configure OSPF area 0 between R6 and R2.
12. Configure iBGP connection between R6 and R2 – use AS 65002.
13. The loopback0 of R2 should be present in the BGP database with an origin attribute of incomplete.
14. Configure an eBGP connection between R6 and R3 in AS 3. Redistribute the EBGP next-hop into OSPF area 0.
15. Configure an eBGP connection between R2 and R3 in AS 3. Redistribute the EBGP next-hop into OSPF area 0.
16. Advertise loopback0 and loopback1 of R3 using network statements.
17. Ensure that the traffic is routed via R2 to reach network 10.1.3.3/32. Configure R3 and use the prefix-list called MED_PL 2 and a route-map called MED_RM2. Use a MED value of 200.
18. Ensure that the traffic is routed via R6 to reach network 10.11.3.3. Configure R3 and use the prefix-list called MED_PL 6 and a route-map called MED_RM6. Use a MED value of 300.
19. On R2 and R6, advertise the network 10.1.26.0/24 with a network statement.
20. On R3, modify the origin of route 10.1.26.0/24 and ensure that this route is reached primarily through R6. Use a prefix-list called ORIGIN_PL and a route-map called ORIGIN_RM.
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22. This network should be advertised to router R4 using the MED 500 and prepending one more AS in the AS-path. Use a prefix-list called ALWAYSCOMPMED_PL and a route-map called ALWAYSCOMPMED_RM.
23. Configure R4 and ensure that R4 always prefers the route with the lowest MED, that is to say the route to R6 is pointing to R7 on R4.
24. Configure an eBGP connection between R2 and R5 (AS 5) and between R4 and R5. Advertise the loopback of R5 into BGP with an origin of “?”.
25. On R4, prepend the AS 65001 4 times when advertising the network 10.1.7.7/32 to R5. The route from R5 to the loopback0 should now be transiting through AS 65002.
26. On R5, the AS-path attribute should be ignored and the route to the 10.1.7.7/32 network has to point towards R4 and not transit through AS 65002 anymore. Use MED to achieve this.
27. On the peering between R2 and R5, shut down the peering if more than 50 BGP updates are advertised from R5 to R2. A syslog message should be sent when more than 40 BGP updates are advertised from R5 to R2.
Helpful Verification Commands
Show ip bgp
Show ip bgp paths
Show ip bgp summary
Show ip bgp neighbor
Technical Verification and Support
To verify your configurations please ensure that you have downloaded the latest “final configurations” from within the iPexpert Member’s Area.
You may also verify your configurations and obtain a detailed overview of why specific commands were used within the accompanying Detailed Solution Guide.
For instructor and developer support, please be sure to submit questions through our interactive support community that’s accessible from the Member’s Area.
This concludes Lab 20 of iPexpert's CCIE Routing & Switching Workbook, Volume 1, Section 2 Copyright© iPexpert. All Rights Reserved.
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