Question

Two routers, R1 and R2, connect an EIGRP domain (AS 100) to an OSPF domain. Both routers perform mutual redistribution between EIGRP and OSPF. Network 10.50.0.0/24 originates natively in EIGRP. Users report intermittent reachability to 10.50.0.0/24 from the OSPF domain, and R2's routing table shows 10.50.0.0/24 pointing back into OSPF instead of via its native EIGRP path. The redistribution is configured with default settings and no route tagging or filtering is applied. What is the MOST likely cause?

Accepted Answer

The route was redistributed into OSPF as an external (O E2) route on R1, and because external OSPF (AD 110) is preferred over EIGRP external (AD 170) on R2, R2 installs the OSPF path, creating a feedback loop.

Answer

OSPF external E2 routes carry a metric of 20 by default, which is lower than the EIGRP composite metric, so R2 always prefers the OSPF path regardless of administrative distance.

Answer

EIGRP auto-summary is enabled, causing 10.50.0.0/24 to be summarized to 10.0.0.0/8 and suppressing the more specific route on R2.

Answer

Split horizon on the EIGRP interface between R1 and R2 prevents R2 from learning 10.50.0.0/24 via EIGRP, forcing it to use the OSPF path.