Lab 9: Path Selection with Weight (First Tiebreaker)

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In this advanced CCNP BGP lab, you will steer a single router's outbound path choice using Cisco's Weight attribute, the very first BGP best-path tiebreaker. R1 (AS 65001) peers eBGP with two ISPs (R2 in AS 65002 and R3 in AS 65003). Both ISPs advertise the same prefix 172.16.50.0/24. Your job is to make R1 prefer the R3 path using the neighbor weight command and verify the outcome using IOS and Linux tools.

Learning objectives

• Configure and verify parallel eBGP sessions over separate /30 transits.
• Originate and receive an identical prefix from two neighbors and view candidate paths.
• Understand and apply BGP Weight to influence a single router's local decision.
• Contrast Weight (local-only) with Local Preference (AS-wide) in best-path order.
• Validate path selection with show ip bgp and data-plane tests from a host.

Troubleshooting focus

• If only one path is visible on R1, confirm both eBGP sessions are configured symmetrically with correct remote-as values and the /30 addressing matches on each side.
• If the 172.16.50.0/24 route is missing, verify Loopback1 at 172.16.50.1/24 exists on both R2 and R3, and that network 172.16.50.0 mask 255.255.255.0 is configured under BGP on each.
• If Weight appears set but not taking effect, ensure the neighbor address in the weight command exactly matches the eBGP neighbor and confirm both paths are otherwise tied.
• If data-plane tests fail from the host, verify the host default gateway, R1 LAN addressing, and that R1 holds a BGP route to 172.16.50.0/24 with next-hop toward R3.