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Two route sources offer exactly 10.60.12.0/24: RIP AD 120 and OSPF AD 110. A separate static route offers 10.60.0.0/16 AD 1. What should a packet to 10.60.12.77 use?
IOS first selects among eligible sources to install a route for the /24, favoring OSPF over RIP by AD. Forwarding then selects the more specific installed /24 over /16.
A low-AD covering /16 does not supersede a valid more-specific /24 during destination forwarding.
For the same /24, the lower AD 110 route wins source selection over RIP AD 120.
Different prefix lengths and AD values do not create equal-cost path entries for the same destination.
At a customer support center, the migration lead forwards a packet to 10.25.5.183. Four installed IPv4 routes are listed; all next hops are usable. Which entry wins the longest-prefix match?
10.25.5.0/24 has a prefix length /24 and is the longest matching installed route for 10.25.5.183; destination lookups prefer specificity before an unrelated metric.
10.25.6.0/25 has a prefix length /25 and does not contain 10.25.5.183, so this route cannot forward the destination.
10.25.0.0/16 has a prefix length /16 and matches 10.25.5.183 but /24 is more specific than /16.
0.0.0.0/0 has a prefix length /0 and matches 10.25.5.183 but /24 is more specific than /0.
At a research campus, an implementation partner forwards a packet to 10.15.153.182. Four installed IPv4 routes are listed; all next hops are usable. Which entry wins the longest-prefix match?
10.15.0.0/16 has a prefix length /16 and is the longest matching installed route for 10.15.153.182; destination lookups prefer specificity before an unrelated metric.
0.0.0.0/0 has a prefix length /0 and matches 10.15.153.182 but /16 is more specific than /0.
10.15.154.0/24 has a prefix length /24 and does not contain 10.15.153.182, so this route cannot forward the destination.
10.15.154.0/25 has a prefix length /25 and does not contain 10.15.153.182, so this route cannot forward the destination.
A routing table contains 10.8.64.0/18 toward a data center and 10.8.96.0/19 toward a security appliance. Both are usable. Which route forwards traffic to 10.8.110.25?
The destination falls in both CIDR ranges. The /19 fixes more destination bits and is the preferred forwarding match.
Covering more addresses makes /18 less specific; it does not make it preferred for a destination also covered by /19.
Next-hop labels have no role in longest-prefix matching.
CIDR summarization permits nested prefixes; a /19 can be a subset of a /18 without invalid routing.
A router learns 10.77.0.0/16 via OSPF (AD 110) and eBGP (AD 20), and both next hops resolve. Which route source is normally selected for that identical prefix by default?
When routes compete for the same destination prefix and both are usable, Cisco IOS prefers the lower administrative distance by default. The BGP route wins over OSPF.
OSPF internal routes use AD 110, which is higher than the typical eBGP AD 20.
Different route sources with unequal AD are not automatically installed as equal-cost forwarding paths.
Multiple routing protocols may operate simultaneously; the router selects among eligible routes by its preference rules.
R1 has an aggregate static route `S 10.60.0.0/16 is directly connected, Null0` and a more specific installed OSPF path to 10.60.5.0/24. What happens to a packet for 10.60.99.1, assuming no other matching routes?
The /24 does not match .99.1, so the covering /16 Null0 route is the longest eligible match and discards the packet, preventing accidental loops for unallocated portions of the summary.
The /24 only covers 10.60.5.0–10.60.5.255; a forwarding route cannot match outside its prefix.
Null0 can be a legitimate static discard route; if its /16 is the best match, a less-specific default would not win.
A summarization route does not imply flood forwarding; the Null0 next hop explicitly discards matching traffic.
At a supply depot, the campus network lead forwards a packet to 10.22.100.167. Four installed IPv4 routes are listed; all next hops are usable. Which entry wins the longest-prefix match?
10.22.100.0/24 has a prefix length /24 and is the longest matching installed route for 10.22.100.167; destination lookups prefer specificity before an unrelated metric.
0.0.0.0/0 has a prefix length /0 and matches 10.22.100.167 but /24 is more specific than /0.
10.22.0.0/16 has a prefix length /16 and matches 10.22.100.167 but /24 is more specific than /16.
10.22.101.0/25 has a prefix length /25 and does not contain 10.22.100.167, so this route cannot forward the destination.
At a retail branch, an implementation partner forwards a packet to 10.133.42.108. Four installed IPv4 routes are listed; all next hops are usable. Which entry wins the longest-prefix match?
10.133.0.0/16 has a prefix length /16 and is the longest matching installed route for 10.133.42.108; destination lookups prefer specificity before an unrelated metric.
10.133.42.128/25 has a prefix length /25 and does not contain 10.133.42.108, so this route cannot forward the destination.
10.133.43.0/24 has a prefix length /24 and does not contain 10.133.42.108, so this route cannot forward the destination.
0.0.0.0/0 has a prefix length /0 and matches 10.133.42.108 but /16 is more specific than /0.
R1 has connected route `C 10.8.12.0/24` and OSPF route `O 10.8.12.128/25`. Both are installed and the /25 next hop is reachable. A packet arrives for 10.8.12.190. What happens?
Once the /25 is installed, it covers .128–.255 and matches the target more specifically than the /24. Routing performs longest-prefix matching before comparing ADs between different prefixes.
Connected-route AD is relevant to choosing sources for the same prefix, not to bypassing a longer matching installed prefix.
More-specific learned routes can coexist with a covering connected route when valid; the overlap is not inherently disallowed.
Two prefixes with different lengths are not same-prefix equal-cost paths, even when one contains the other.
A default static route points to 198.51.100.1. The router loses its connected network covering that next hop. What should an engineer expect when checking active forwarding entries?
A next-hop-only route depends on an active route or adjacency resolving that next hop. A configured line does not guarantee an installed usable route.
A covering destination prefix does not fix an unreachable next hop.
Route recursion cannot turn an arbitrary neighbor address into a router-owned interface.
The failure of one static next-hop resolution does not, by itself, invalidate unrelated dynamic routes.
R1's installed IPv4 table selects route `S 10.60.0.0/16 via 192.0.2.2, Gi0/0`. The LAN has already resolved 192.0.2.2 to MAC 00aa.bbcc.ddee. What Ethernet destination address does R1 use for a packet to 10.60.2.5?
The routing decision picks next-hop 192.0.2.2, and Ethernet encapsulation uses that local adjacency's MAC. The destination IP remains 10.60.2.5 in the routed packet.
A remote subnet destination MAC is not directly reachable on the local Ethernet; the router addresses the adjacent next hop instead.
Broadcast is used for certain discoveries, not each normal resolved unicast forwarding frame.
The source host's MAC is not the outgoing destination MAC; the forwarding adjacency points to the next-hop router.
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