First, the essential ideas
- Default route
- The IPv4 prefix 0.0.0.0/0, matching every destination but selected only when no installed, more-specific matching route applies.
- Host route
- A /32 IPv4 route covering exactly one address. It can override a matching network or default route regardless of their lower administrative distance.
- Administrative distance
- A local preference between eligible route sources for the same prefix; lower values are preferred. It is not a latency measurement or a comparison across different prefix lengths.
- Floating static route
- A configured static route with higher distance than its intended same-prefix primary. It can become selected when that primary is no longer eligible.
- Null0
- A logical discard interface. A selected route to Null0 intentionally drops matching traffic rather than forwarding it to another device.
- Failover and failback
- Failover moves work to an available alternative after the preferred choice is lost. Failback restores the preferred choice; neither term promises zero packet loss.
- Fully specified route
- A static route naming both the local exit interface and adjacent next-hop address, making the intended Ethernet adjacency explicit.
- Loopback endpoint
- A software interface belonging to a router. Its address can be the actual source or destination of this lab's ping without a hidden host or LAN.
Keep two decisions separate. Route installation chooses among candidates for an identical prefix, while packet forwarding chooses the longest matching installed prefix. A high-distance /32 is not a backup for a low-distance /0. This lesson deliberately creates both situations so the distinction is visible.
See the idea
Primary or backup, never both in series
Gi0/0 and Gi0/1 are alternative R1-R2 links. The backup needs a return route too; a /32 discard overrides either default.
Prefer the primary
The Gi0/0 default uses 192.0.2.2 at AD 1; R2's primary return route uses 192.0.2.1.
What this model leaves out: Route-option comparison, not a serial topology. Each record describes a separate direct R1-R2 link. Loopback endpoints reside on those routers. No Internet or measured failover time.
Full visual explanation and references
Two unconnected records compare R1-R2 alternatives: primary Gi0/0 at AD 1 and backup Gi0/1 at AD 200. Both carry the same R1 198.51.100.10 to R2 203.0.113.10 endpoint exchange.
Route-option comparison, not a serial topology. Each record describes a separate direct R1-R2 link. Loopback endpoints reside on those routers. No Internet or measured failover time.
- Prefer the primary
The Gi0/0 default uses 192.0.2.2 at AD 1; R2's primary return route uses 192.0.2.1.
www.cisco.com - Use the alternate link
With both Gi0/0 ports down, Gi0/1 carries requests via 192.0.2.6 and replies via 192.0.2.5 at AD 200.
www.cisco.com - A host route beats both
After restoring links, a /32 Null0 entry at R1 discards the target's traffic instead of using either default.
www.cisco.com
One idea at a time
Start with something familiar.
Draw R1 and R2 with a top cable labeled Gi0/0 primary and a bottom cable labeled Gi0/1 backup. Put the source and destination loopbacks inside their respective routers, not behind invented PCs.
Why learn this?
A configured backup can look reassuring while never becoming eligible, or while a more-specific bad route still captures the traffic. Checking only whether a default exists misses both problems.
An everyday comparison
A building can have a general exit sign and a specific instruction for one room. The room-specific instruction takes precedence for that room, while another exit can replace a closed general exit.
What happens in a network
The specific room resembles a host prefix; the general sign resembles a default. The two alternative exits resemble routes for the same prefix with different local preferences.
Where the comparison stopsSigns do not model neighbor resolution, independent return paths or router failure detection. This comparison explains scope, not measured convergence time.
Follow one worked example
- Record the primary default.
R1 selects /0 through .2 on Gi0/0 while the AD 200 default remains configured.
Why: Only equal-prefix candidates compete by distance in this comparison.
- Disable both primary endpoints.
The primary interface dependencies disappear, leaving the Gi0/1 defaults and return routes eligible.
Why: Explicit changes at both ends avoid assuming a virtual cable propagates physical carrier state.
- Add one /32 discard after restoring links.
Traffic to 203.0.113.10 selects Null0 even though the default is healthy.
Why: The host prefix is longer; its distance 200 is not compared against the default's distance 1.
Your first small task
For destination 203.0.113.10, compare an installed /0 via .2 at AD 1 with a /32 Null0 at AD 200. Write the selected prefix and the expected forwarding action.
Show a hint
Count the matching prefix bits before comparing administrative distance.
Check the expected result
The /32 wins for that one address, and Null0 discards the packet. The default can still serve other destinations.
Pause and explain it in your own words
Why is a configured AD 200 default normally absent from the selected table?
Show a hint
It competes against another route for the identical /0 prefix.
Show the explanation
The eligible AD 1 default is preferred for /0. The AD 200 line remains configured as an alternative; its absence from the selected route table is expected, not proof of a missing command.
Short answer
What should you understand today?
A default route handles otherwise unmatched destinations. A host route matches one address more specifically. A floating static is a higher-distance alternative to the same prefix, not a universal outage detector. Check which prefix matches first, which same-prefix route is installed, and whether both request and reply can actually traverse the chosen links.
Before you begin
Learning targets
- Complete Day 31's source-qualified ping and separate return-route exercise.
- Use two fresh entitled CML 2.10 IOSv 15.9M nodes with two mapped Ethernet links.
- Know /30 transit masks and /24 loopback networks before entering the supplied commands.
- Distinguish default, host and floating route purposes.
- Configure identical-prefix alternatives with distances 1 and 200.
- Verify failover and return-path behavior separately.
- Explain why a /32 discard beats a /0 default.
- Restore both interfaces and remove only the deliberate host fault.
Words you will meet
Open a word when you need its meaning. You do not need to memorize the whole list before reading.
Default route
The IPv4 prefix 0.0.0.0/0, matching every destination but selected only when no installed, more-specific matching route applies.
Host route
A /32 IPv4 route covering exactly one address. It can override a matching network or default route regardless of their lower administrative distance.
Administrative distance
A local preference between eligible route sources for the same prefix; lower values are preferred. It is not a latency measurement or a comparison across different prefix lengths.
Floating static route
A configured static route with higher distance than its intended same-prefix primary. It can become selected when that primary is no longer eligible.
Null0
A logical discard interface. A selected route to Null0 intentionally drops matching traffic rather than forwarding it to another device.
Failover and failback
Failover moves work to an available alternative after the preferred choice is lost. Failback restores the preferred choice; neither term promises zero packet loss.
Fully specified route
A static route naming both the local exit interface and adjacent next-hop address, making the intended Ethernet adjacency explicit.
Loopback endpoint
A software interface belonging to a router. Its address can be the actual source or destination of this lab's ping without a hidden host or LAN.
A default is a fallback destination range
The command ip route 0.0.0.0 0.0.0.0 supplies a next hop for destinations without a more-specific installed match. A default does not provide Internet service by itself, distribute routes to peers or repair a missing return path. In this lab it reaches only R2's explicit loopback endpoint. R2 has no onward provider and needs no default of its own.
- A /0 can be selected without any Internet attachment.
- Do not use ip default-gateway as a substitute on an IP-routing router.
A floating route must compete for the same prefix
A normal static route has default distance 1. Here distance 200 makes another /0 less preferred while both links are usable. Use a value greater than the intended primary and less than 255; distance 255 does not install. Raising distance does not reduce bandwidth or delay a packet. The same idea applies to a static backup for a dynamic route, but this lab uses two statics so no protocol is hidden.
- Inspect running configuration as well as the selected table.
- Equal-distance eligible alternatives are not the intended floating-primary design.
Interface failure is not every possible service failure
Both interface and next-hop information are specified to tie each route to its intended Ethernet link. Removing that local interface dependency makes the primary ineligible in this exercise. A remote server failure with the local interface still up may leave the route installed. More advanced tracking can address some cases, but no tracking object or probe is configured here.
- Test both forwarding directions after withdrawing the primary.
- Never infer end-service health solely from route installation.
A host exception can defeat the default
An IPv4 host route uses mask 255.255.255.255. Longest-prefix lookup selects it for exactly that address even if a matching default has a lower distance. Null0 is a deliberate discard, not a router with an unresolved address. After the backup test, the lab temporarily adds a host discard and verifies that the route lookup explains the failed exchange.
- A higher-distance more-specific route is not automatically a backup.
- Check the exact failed destination, not just the default route display.
Keep evidence and exam scope explicit
Use the same loopback source and destination at baseline, on the backup, during the host fault and after restoration. Preserve selected prefix, exit interface and next hop with each observation. The current v1.1 window ends February 2, 2027; the announced v2.0 starts February 3. This lesson supplies the IPv4 default, host and floating portion, while Day 33 provides the IPv6 counterpart.
- No runtime, pixel QA or independent review is claimed here.
- The complete static objective requires both address families and all reserved route types.
Real-world walkthrough
The backup activated, but one address still failed
In a hypothetical isolated branch test, an operator sees the backup default installed and assumes every destination is covered. One diagnostic address still fails because a forgotten host discard is more specific. Repeatedly changing the default's distance cannot override that /32.
- Identify the exact failing destination and the packet's source.
- Inspect its longest matching prefix instead of only the gateway-of-last-resort line.
- Confirm whether the selected action is a next hop or Null0.
- Remove only the authorized mistaken host entry, leaving both default preferences unchanged.
- Repeat the same exchange and retain both lookup states as the explanation.
Guided GNS3 lab
Two defaults, one backup and one host exception
Establish a fixed-source baseline, withdraw both primary endpoints, test the backup, restore the link and diagnose a temporary host discard. Predicted outcomes below are not fabricated router transcripts.
Addressing plan
| Device | Interface | Address | Purpose |
|---|---|---|---|
| R1 | Gi0/0 | 192.0.2.1/30 | Primary transit |
| R2 | Gi0/0 | 192.0.2.2/30 | Primary neighbor |
| R1 | Gi0/1 | 192.0.2.5/30 | Backup transit |
| R2 | Gi0/1 | 192.0.2.6/30 | Backup neighbor |
| R1 | Loopback0 | 198.51.100.10/24 | Fixed source |
| R2 | Loopback0 | 203.0.113.10/24 | Final destination |
Set up the lab
- Use Cisco Modeling Labs 2.10 with its legally entitled bundled IOSv 15.9M reference image. Record the complete show version release; do not export that image to GNS3. No paid API is involved.
- Create fresh nodes and only the listed links. No External Connector, NAT node, bridge, public uplink or production network is permitted. Leave console access independent of the test data links.
- IOSv examples use GigabitEthernet0/0 and GigabitEthernet0/1. Confirm those exact ports in the workbench and show ip interface brief before configuring; if your image differs, document an explicit port substitution first.
- Decline the initial configuration dialog on a new authorized node, press Enter to reach the prompt, then use enable. Do not bypass unknown credentials. All displayed expected results are predictions, not author runtime.
- Without an entitled compatible image, complete the address and route-selection worksheet only. Mark command execution, packet forwarding and recovery unmeasured.
Configure R1's two transit links
In the isolated CML workbench, select R1, open its Console tab and connect before typing. Start at > or #; use end first if a prior task left configuration mode. Record show version first, confirm both mapped cables, then address the two ports.
enable
configure terminal
interface GigabitEthernet0/0
ip address 192.0.2.1 255.255.255.252
no shutdown
exit
interface GigabitEthernet0/1
ip address 192.0.2.5 255.255.255.252
no shutdown
endWhat each command means
enable- Enter authorized privileged EXEC mode; this does not change the network configuration.
configure terminal- Enter global configuration mode on this named router; accepted changes affect its running state.
interface GigabitEthernet0/0- Select the primary Ethernet link.
ip address 192.0.2.1 255.255.255.252- Assign this endpoint of the primary /30.
no shutdown- Enable the primary interface.
exit- Return to global configuration.
interface GigabitEthernet0/1- Select the independent backup cable.
ip address 192.0.2.5 255.255.255.252- Assign this endpoint of the backup /30.
no shutdown- Enable the backup interface.
end- Return to privileged EXEC; this neither saves nor reverses accepted configuration changes.
- What you should see
- R1's primary and backup ports have different /30 subnets.
- Why this step matters
- Distinct transit prefixes prevent accidental overlap or next-hop ambiguity.
Configure R2's opposite endpoints
In the isolated CML workbench, select R2, open its Console tab and connect before typing. Start at > or #; use end first if a prior task left configuration mode. Record show version first and use the opposite usable addresses on the matching cables.
enable
configure terminal
interface GigabitEthernet0/0
ip address 192.0.2.2 255.255.255.252
no shutdown
exit
interface GigabitEthernet0/1
ip address 192.0.2.6 255.255.255.252
no shutdown
endWhat each command means
enable- Enter authorized privileged EXEC mode; this does not change the network configuration.
configure terminal- Enter global configuration mode on this named router; accepted changes affect its running state.
interface GigabitEthernet0/0- Select the primary Ethernet link.
ip address 192.0.2.2 255.255.255.252- Assign this endpoint of the primary /30.
no shutdown- Enable the primary interface.
exit- Return to global configuration.
interface GigabitEthernet0/1- Select the independent backup cable.
ip address 192.0.2.6 255.255.255.252- Assign this endpoint of the backup /30.
no shutdown- Enable the backup interface.
end- Return to privileged EXEC; this neither saves nor reverses accepted configuration changes.
- What you should see
- Both links should become usable once each endpoint is enabled.
- Why this step matters
- The backup is a real second declared connection, not an imaginary alternate next hop.
Add source and competing defaults
In the isolated CML workbench, select R1, open its Console tab and connect before typing. Start at > or #; use end first if a prior task left configuration mode. Create the fixed source and both /0 candidates; only the lower-distance candidate should be preferred.
enable
configure terminal
interface Loopback0
ip address 198.51.100.10 255.255.255.0
exit
ip route 0.0.0.0 0.0.0.0 GigabitEthernet0/0 192.0.2.2
ip route 0.0.0.0 0.0.0.0 GigabitEthernet0/1 192.0.2.6 200
endWhat each command means
enable- Enter authorized privileged EXEC mode; this does not change the network configuration.
configure terminal- Enter global configuration mode on this named router; accepted changes affect its running state.
interface Loopback0- Create the source software endpoint.
ip address 198.51.100.10 255.255.255.0- Assign the explicit source subnet.
exit- Return to global routing configuration.
ip route 0.0.0.0 0.0.0.0 GigabitEthernet0/0 192.0.2.2- Add the primary default with implicit distance 1.
ip route 0.0.0.0 0.0.0.0 GigabitEthernet0/1 192.0.2.6 200- Add a same-prefix backup using distance 200.
end- Return to privileged EXEC; this neither saves nor reverses accepted configuration changes.
- What you should see
- The primary default should install while the backup remains configured.
- Why this step matters
- Distance is meaningful here because the two routes have exactly the same prefix.
Add destination and two return routes
In the isolated CML workbench, select R2, open its Console tab and connect before typing. Start at > or #; use end first if a prior task left configuration mode. Give both possible request paths a matching return capability.
enable
configure terminal
interface Loopback0
ip address 203.0.113.10 255.255.255.0
exit
ip route 198.51.100.0 255.255.255.0 GigabitEthernet0/0 192.0.2.1
ip route 198.51.100.0 255.255.255.0 GigabitEthernet0/1 192.0.2.5 200
endWhat each command means
enable- Enter authorized privileged EXEC mode; this does not change the network configuration.
configure terminal- Enter global configuration mode on this named router; accepted changes affect its running state.
interface Loopback0- Create the final destination endpoint.
ip address 203.0.113.10 255.255.255.0- Assign the destination address to R2 itself.
exit- Return to global route configuration.
ip route 198.51.100.0 255.255.255.0 GigabitEthernet0/0 192.0.2.1- Add the preferred return network route.
ip route 198.51.100.0 255.255.255.0 GigabitEthernet0/1 192.0.2.5 200- Add the higher-distance backup return route.
end- Return to privileged EXEC; this neither saves nor reverses accepted configuration changes.
- What you should see
- R2 should prefer Gi0/0 for replies to the fixed source.
- Why this step matters
- A forward backup alone cannot guarantee a successful exchange.
Record a primary baseline
In the isolated CML workbench, select R1, open its Console tab and connect before typing. Start at > or #; use end first if a prior task left configuration mode. Do not inject a fault until this exact source-target exchange works in an actual run.
enable
show running-config | include ^ip route
show ip route 203.0.113.10
ping 203.0.113.10 source 198.51.100.10What each command means
enable- Enter authorized privileged EXEC mode to inspect this named router.
show running-config | include ^ip route- Compare both configured defaults.
show ip route 203.0.113.10- Identify the selected /0 and primary next hop.
ping 203.0.113.10 source 198.51.100.10- Test both route directions with the explicit source.
- What you should see
- Expect the primary next hop and successful replies after neighbor resolution.
- Why this step matters
- This is the reference against which backup and host-fault results are compared.
Withdraw R1's primary port
In the isolated CML workbench, select R1, open its Console tab and connect before typing. Start at > or #; use end first if a prior task left configuration mode. Change only Gi0/0, retaining console access and the untouched backup.
enable
configure terminal
interface GigabitEthernet0/0
shutdown
endWhat each command means
enable- Enter authorized privileged EXEC mode; this does not change the network configuration.
configure terminal- Enter global configuration mode on this named router; accepted changes affect its running state.
interface GigabitEthernet0/0- Select only the primary port.
shutdown- Administratively remove the primary interface dependency.
end- Return to privileged EXEC; this neither saves nor reverses accepted configuration changes.
- What you should see
- R1's primary route should become ineligible.
- Why this step matters
- Console access is independent of the interface intentionally disabled.
Withdraw R2's primary port
In the isolated CML workbench, select R2, open its Console tab and connect before typing. Start at > or #; use end first if a prior task left configuration mode. Disable the opposite primary endpoint explicitly; do not depend on virtual carrier propagation.
enable
configure terminal
interface GigabitEthernet0/0
shutdown
end
show ip route 198.51.100.10What each command means
enable- Enter authorized privileged EXEC mode; this does not change the network configuration.
configure terminal- Enter global configuration mode on this named router; accepted changes affect its running state.
interface GigabitEthernet0/0- Select R2's primary port.
shutdown- Withdraw the preferred return-path interface.
end- Return to privileged EXEC; this neither saves nor reverses accepted configuration changes.
show ip route 198.51.100.10- Check that the return /24 now uses .5 on Gi0/1.
- What you should see
- Expect the distance 200 return route via Gi0/1.
- Why this step matters
- Both directions now have a deterministic primary-interface withdrawal.
Verify the backup exchange
In the isolated CML workbench, select R1, open its Console tab and connect before typing. Start at > or #; use end first if a prior task left configuration mode. Inspect the selected route before repeating the identical endpoint test.
enable
show ip route 203.0.113.10
ping 203.0.113.10 source 198.51.100.10What each command means
enable- Enter authorized privileged EXEC mode to inspect this named router.
show ip route 203.0.113.10- Verify the default now selects .6 on Gi0/1 with distance 200.
ping 203.0.113.10 source 198.51.100.10- Test the same endpoints across the backup pair.
- What you should see
- Expect backup selection and recovery; record real loss rather than assuming zero.
- Why this step matters
- This tests usable forwarding, not merely a configured floating route.
Restore R1's primary port
In the isolated CML workbench, select R1, open its Console tab and connect before typing. Start at > or #; use end first if a prior task left configuration mode. Undo only the documented interface change.
enable
configure terminal
interface GigabitEthernet0/0
no shutdown
endWhat each command means
enable- Enter authorized privileged EXEC mode; this does not change the network configuration.
configure terminal- Enter global configuration mode on this named router; accepted changes affect its running state.
interface GigabitEthernet0/0- Select the withdrawn primary port.
no shutdown- Restore R1's original administrative state.
end- Return to privileged EXEC; this neither saves nor reverses accepted configuration changes.
- What you should see
- R1 can return to its primary once the opposite endpoint is enabled.
- Why this step matters
- The exact inverse preserves all routing preferences and backup configuration.
Restore R2 and verify return
In the isolated CML workbench, select R2, open its Console tab and connect before typing. Start at > or #; use end first if a prior task left configuration mode. Restore the far endpoint and confirm the preferred return route returns.
enable
configure terminal
interface GigabitEthernet0/0
no shutdown
end
show ip route 198.51.100.10What each command means
enable- Enter authorized privileged EXEC mode; this does not change the network configuration.
configure terminal- Enter global configuration mode on this named router; accepted changes affect its running state.
interface GigabitEthernet0/0- Select R2's original primary endpoint.
no shutdown- Restore primary-link availability.
end- Return to privileged EXEC; this neither saves nor reverses accepted configuration changes.
show ip route 198.51.100.10- Verify the return /24 again prefers .1 on Gi0/0.
- What you should see
- Expect distance 1 return selection after the link recovers.
- Why this step matters
- Failback evidence must include the reply route, not only the forward default.
Install the one-host fault
In the isolated CML workbench, select R1, open its Console tab and connect before typing. Start at > or #; use end first if a prior task left configuration mode. Add this temporary discard only after both primary ports are restored.
enable
configure terminal
ip route 203.0.113.10 255.255.255.255 Null0 200
endWhat each command means
enable- Enter authorized privileged EXEC mode; this does not change the network configuration.
configure terminal- Enter global configuration mode on this named router; accepted changes affect its running state.
ip route 203.0.113.10 255.255.255.255 Null0 200- Discard exactly the destination host using a more-specific /32.
end- Return to privileged EXEC; this neither saves nor reverses accepted configuration changes.
- What you should see
- The /32 should install independently of the matching /0.
- Why this step matters
- The higher distance does not make a different-length prefix a floating default.
Explain the host-specific failure
In the isolated CML workbench, select R1, open its Console tab and connect before typing. Start at > or #; use end first if a prior task left configuration mode. Record the chosen prefix alongside the same failed exchange.
enable
show ip route 203.0.113.10
ping 203.0.113.10 source 198.51.100.10What each command means
enable- Enter authorized privileged EXEC mode to inspect this named router.
show ip route 203.0.113.10- Identify the /32 Null0 match instead of the default.
ping 203.0.113.10 source 198.51.100.10- Repeat the original exchange now captured by the discard.
- What you should see
- Expect the /32 and failed exchange despite the healthy default.
- Why this step matters
- This isolates longest-prefix selection from same-prefix distance preference.
Remove only the host fault
In the isolated CML workbench, select R1, open its Console tab and connect before typing. Start at > or #; use end first if a prior task left configuration mode. Leave both valid defaults and all interfaces unchanged.
enable
configure terminal
no ip route 203.0.113.10 255.255.255.255 Null0 200
endWhat each command means
enable- Enter authorized privileged EXEC mode; this does not change the network configuration.
configure terminal- Enter global configuration mode on this named router; accepted changes affect its running state.
no ip route 203.0.113.10 255.255.255.255 Null0 200- Remove the exact temporary host discard.
end- Return to privileged EXEC; this neither saves nor reverses accepted configuration changes.
- What you should see
- The destination lookup should again fall through to the default.
- Why this step matters
- A targeted inverse avoids damaging the independently verified backup design.
Retest the original primary path
In the isolated CML workbench, select R1, open its Console tab and connect before typing. Start at > or #; use end first if a prior task left configuration mode. Compare route and traffic evidence with the first baseline before stopping.
enable
show ip route 203.0.113.10
ping 203.0.113.10 source 198.51.100.10What each command means
enable- Enter authorized privileged EXEC mode to inspect this named router.
show ip route 203.0.113.10- Verify the /0 through the primary .2 neighbor.
ping 203.0.113.10 source 198.51.100.10- Repeat the original fixed-source exchange after all restoration.
- What you should see
- Expect restored primary selection and replies; preserve actual output.
- Why this step matters
- The experiment closes only when its original behavior is restored.
Verify
- Record both configured defaults and the single preferred route at baseline.
- Check backup routes in both directions with both primary ports down.
- Show that the /32 selects Null0 despite the lower-distance default.
- Retest the exact source and destination after removing the host fault.
Troubleshoot
- If the backup is absent, compare identical prefixes, distance, interface state and adjacent next-hop addressing.
- If only one direction moved, verify the other primary port was deliberately shut and the return backup exists.
- If one destination fails after failback, inspect its longest matching route before changing default distances.
GNS3 does not provide Cisco images. Use software only when the applicable license or entitlement permits that environment. Do not share or redistribute image files. Cisco Modeling Labs is the official alternative; its reference images are licensed for use within CML unless separately licensed. A paper exercise needs no image, but does not establish hands-on competence. Virtual routers do not reproduce physical radios, PoE delivery, hardware forwarding rates or failover timing.
- Restore both Gi0/0 interfaces and remove the temporary /32 Null0 route.
- Keep both intended backup routes; retain observations privately and stop the isolated project.
Practice set
Answer before you reveal
01Does a default route prove Internet access?
This isolated topology ends at R2's loopback and contains no provider. Route syntax cannot create an external service.
02Why is distance 200 used on the second default?
The same-prefix primary wins while eligible. A distance of 255 would not be a usable fallback.
03Why disable both primary ports?
Virtual carrier signaling is not assumed. The test states precisely what failed and keeps the backup links untouched.
04Why does the /32 beat the /0?
Distance chooses among equal-prefix candidates; it does not let a default override an installed host route.
05Will a failed remote service always activate the backup?
This lab detects an interface dependency withdrawal, not application health. No tracking probe is configured.
06Which missing route can break backup replies?
A request and its reply undergo independent lookups. Preserve the source address to test the planned return dependency.
Knowledge check
Quiz: prove the reasoning
Keep these
Technical takeaways
- Defaults cover otherwise unmatched destinations, not guaranteed Internet service.
- Floating routes compete with primaries for the same prefix.
- Explicit interfaces constrain the intended Ethernet adjacency.
- Both directions need a usable backup route.
- A host discard can override a healthy default.
- No loss or convergence duration is claimed without a real measurement.