Overlay /32 host routes from EVPN are exploding on county leaves and stressing RIB and FIB, even though the underlay still has only a modest number of loopbacks and fabric links. What distinction should engineers make when diagnosing the scale problem?
Select an answer to reveal the explanation.
Short Explanation
Underlay routes are the street map; overlay host routes are every house number glued onto that map. When the house-number list blows up, that is an overlay scale issue—do not confuse it with a skinny underlay that still only has a handful of fabric prefixes.
Full Explanation
IP fabrics separate underlay infrastructure reachability (loopbacks, link subnets) from overlay host and subnet routes carried in EVPN/VXLAN. A healthy underlay can still be overwhelmed by overlay host-route explosion in the leaf RIB/FIB. Mitigation belongs in overlay design (aggregation, routing model, route targets, host-route policy)—not by treating underlay and overlay as one identical limit, shrinking MTU, or disabling spine BGP.