The configuration exhibit demonstrates a classic scenario where mismatched static routing leads to a routing loop . Router R1 is configured with a default route ( 0.0.0.0/0 ) pointing to R2 as its next hop. Conversely, R2 is configured with a broad static route for 10.1.0.0/16 pointing back to R1 .
If a user sends a packet to an unassigned IP address such as 10.1.99.1 , the following sequence occurs:
R1 receives the packet and consults its routing table. Finding no specific match for the 10.1.99.1 host, it uses the default route and forwards the packet to R2 .
R2 receives the packet and identifies that 10.1.99.1 falls within its defined static route for 10.1.0.0/16 .
Following its configuration, R2 forwards the packet back to R1 . This process repeats indefinitely—or until the packet ' s Time to Live (TTL) reaches zero—because the broad summary on R2 encompasses addresses that R1 does not actually have a local path for. This illustrates the critical importance of ensuring that summary routes or default routes do not overlap in a way that creates circular forwarding paths for non-existent destinations. Reference: Routing Fundamentals, Static Route Configuration, Routing Loops and TTL.
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