352-001 · Question #420
After a large EIGRP network had automatic summarization enabled throughout, it started experiencing routing loops. Which action should you take to quickly resolve the routing loops yet continue to…
The correct answer is A. Replace the automatic summarization with more specific summary routes. EIGRP automatic summarization to classful boundaries causes routing loops in discontiguous networks; replacing it with manual, specific summary routes resolves this quickly while preserving summarization.
Question
After a large EIGRP network had automatic summarization enabled throughout, it started experiencing routing loops. Which action should you take to quickly resolve the routing loops yet continue to perform summarization?
Options
- AReplace the automatic summarization with more specific summary routes.
- BRedesign the IP addressing scheme.
- CRedistribute connected routes at major IP network boundaries.
- DIncrease the AD of the automatically summarized routes.
How the community answered
(48 responses)- A71% (34)
- B15% (7)
- C4% (2)
- D10% (5)
Why each option
EIGRP automatic summarization to classful boundaries causes routing loops in discontiguous networks; replacing it with manual, specific summary routes resolves this quickly while preserving summarization.
Automatic summarization in EIGRP summarizes to classful network boundaries, which creates discontiguous subnets and routing loops when the same major network exists at multiple locations. Replacing automatic summarization with manually configured, more specific summary routes gives precise control over what is advertised and eliminates the discontiguous network problem immediately. This approach is the fastest resolution because it preserves summarization benefits while removing the loop-inducing classful boundary aggregation.
Redesigning the IP addressing schema eliminates discontiguous networks but is a long-term, time-consuming effort rather than a quick fix for active routing loops.
Redistributing connected routes at major network boundaries does not address the root cause of classful summarization creating discontiguous subnets and loops.
Increasing the administrative distance of automatically summarized routes alters route preference but does not remove the discontiguous network condition that is causing the loop.
Concept tested: EIGRP automatic summarization and discontiguous network loop prevention
Source: https://www.cisco.com/c/en/us/support/docs/ip/enhanced-interior-gateway-routing-protocol-eigrp/16406-eigrp-toc.html
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