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350-401 Practice Question: Is configuring BGP on a Cisco router that…
A network engineer is configuring BGP on a Cisco router that connects to two ISPs. The router has a default route pointing to each ISP. The engineer wants to load balance outbound traffic across both ISPs. The router receives a default route from both ISPs. Which BGP configuration approach will allow the router to install both default routes in the routing table and load balance traffic?
⚠ Common exam trap
Cisco often tests the nuance that simply having equal BGP path attributes (like local preference) does not enable multipath installation; candidates must remember that `maximum-paths` and `multipath-relax` are explicitly required to install and load balance multiple BGP routes, even for default routes.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Configure the maximum-paths command under the BGP address family and use the bgp bestpath as-path multipath-relax command.
The `maximum-paths` command under the BGP address family enables the router to install multiple paths for the same prefix (in this case, the default route 0.0.0.0/0) into the routing table. The `bgp bestpath as-path multipath-relax` command is necessary because the two default routes from different ISPs will have different AS_PATH lengths; this command relaxes the requirement for equal AS_PATH length, allowing the router to consider them as multipath candidates. Together, they allow both default routes to be installed and used for load balancing outbound traffic.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Configure the maximum-paths command under the BGP address family and use the bgp bestpath as-path multipath-relax command.
Why this is correct
The BGP best-path algorithm normally installs only one route per prefix into the routing table. Configuring maximum-paths under the BGP address family sets the maximum number of eligible paths that can be installed, while the bgp bestpath as-path multipath-relax command instructs BGP to disregard AS_PATH length differences when selecting these multipath candidates. Together, they enable load balancing across multiple default routes from different ISPs even when the AS_PATH lengths are not identical.
- ✗
Configure the network command to advertise the default route from both ISPs.
Why it's wrong here
The network command is a route-origination tool: it tells BGP to advertise a prefix that already exists in the local routing table. It does not influence how incoming eBGP default routes from ISPs are evaluated or installed. Advertising 0.0.0.0/0 with the network command would only send a default route to neighbors, not cause two received default routes to be used for load balancing, and doing so could even create unintended routing loops.
- ✗
Set the local preference to the same value on both default routes.
Why it's wrong here
Local preference is a BGP attribute used during best-path selection to rank routes leaving an AS. Setting the same local preference on both default routes makes them tie at that step, but BGP then applies subsequent tie-breakers, such as AS_PATH length, MED, router ID, and neighbor IP address, resulting in a single best path. Without an explicit multipath configuration under the address family, only that one path is installed in the RIB, so equal local preference alone cannot produce load balancing.
- ✗
Use the redistribute command to redistribute the default routes into BGP.
Why it's wrong here
Redistribution is used to inject routes from one routing protocol into another (for example, static or EIGRP into BGP). The default routes in question are already present in the BGP table because they were learned over eBGP from the ISPs; redistributing them back into BGP is not necessary and is generally unsupported by default, as BGP does not redistribute its own routes. Even if redistribution were attempted, it would not alter the BGP best-path selection process—installing multiple paths still requires the maximum-paths and multipath-relax feature.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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