First, the essential ideas
- Layer 2 switchport
- A switchport forwards Ethernet frames within VLANs. An access port belongs to one ordinary data VLAN; an 802.1Q trunk can carry multiple VLANs.
- SVI
- A switched virtual interface gives a switch a logical IP attachment to one VLAN. On a routing-capable switch it can be that VLAN's gateway; merely creating it does not enable transit routing.
- Routed physical port
- A physical interface configured with no switchport becomes a Layer 3 port with an IP address on the port itself. It is not an access member or a trunk for the old VLAN.
- IP routing
- IP routing enables packet forwarding between IP interfaces on a capable switch. A management-only default gateway setting is not a replacement for routing configuration.
- Autostate
- Normal SVI operational state depends on an active VLAN, an enabled SVI and at least one eligible up Layer 2 member in forwarding state. Platform exceptions exist; this lesson uses the normal IOSvL2 model.
- Connected route
- An operational addressed IP interface supplies a connected network route. The route can disappear when the interface's protocol goes down even though the address remains in configuration.
- Syslog
- Syslog records device events. A message has a facility, severity and mnemonic plus descriptive content. A recorded state transition is evidence of an event, not automatic proof of its root cause.
- Console and control test
- Console is direct management of the named node. A control test follows an unaffected path during the fault, helping distinguish selective VLAN failure from complete device failure.
Place the IP address where the design actually needs it. An access port carries a VLAN; an SVI attaches routing to that VLAN; a routed port attaches routing directly to a physical link. The lab uses all three so their roles cannot be confused.
See the idea
Three interfaces, three roles
A switchport carries a VLAN, an SVI attaches routing to it, and a routed port has its own IP network.
Carry endpoint frames
Gi0/0 assigns H1's untagged frames to VLAN 10. It has no gateway IP address on the access port.
What this model leaves out: Conceptual interface comparison, not a cable diagram. It omits hardware forwarding internals and does not imply any performance measurement.
Full visual explanation and references
Three interface records compare an access port, an SVI gateway and a routed physical port. Their different roles are shown without implying extra devices.
Conceptual interface comparison, not a cable diagram. It omits hardware forwarding internals and does not imply any performance measurement.
- Carry endpoint frames
Gi0/0 assigns H1's untagged frames to VLAN 10. It has no gateway IP address on the access port.
www.cisco.com - Route through the SVI
Vlan10 holds the local gateway address. Its normal operational state depends on active forwarding VLAN membership.
www.cisco.com - Use a separate subnet
Gi0/2 uses no switchport and a /30 address toward R2. It is not a VLAN member that keeps Vlan20 up.
www.cisco.com
One idea at a time
Start with something familiar.
Draw three rows: Gi0/0 access VLAN 10, Vlan10 gateway 192.0.2.1, and Gi0/2 routed 203.0.113.1/30. Notice that a physical access port and its VLAN gateway occupy different rows.
Why learn this?
An address in configuration can survive after its usable network attachment disappears. Checking SVI dependencies explains failures that repeated address re-entry cannot repair.
An everyday comparison
A department can have a shared reception point used by many doors, while another service has a dedicated entrance. Closing the last department door makes its reception unreachable from that department.
What happens in a network
The shared reception resembles an SVI attached to a VLAN's member ports. The dedicated entrance resembles a routed physical port with its own subnet.
Where the comparison stopsSVI state follows defined platform logic, not physical building rules. A real VLAN can also have forwarding trunk members, so one closed access port does not always remove the SVI.
Follow one worked example
- Separate Layer 2 attachment from Layer 3 addressing.
The access ports receive endpoint frames in VLANs 10 and 20. Their SVI addresses provide the local gateways.
Why: Assigning a gateway to an SVI is different from converting the endpoint's cable into a routed port.
- Verify routing and interface dependencies.
IP routing allows forwarding between operational SVIs; each VLAN needs active forwarding membership.
Why: Neither a configured address nor the routing command alone proves the endpoint path.
- Remove and restore one known dependency.
Shutting Gi0/1 removes the only VLAN 20 member. Its SVI should lose operational state, then recover when the port returns.
Why: The experiment connects a physical member event to logical gateway and route state.
Your first small task
On paper, list what must be true for Vlan20 to be up/up under normal autostate when Gi0/1 is its only member. Then predict the effect of shutting Gi0/1 without deleting the SVI address.
Show a hint
Do not confuse a configured IP address with a usable Layer 2 attachment.
Check the expected result
VLAN 20 must exist and be active, its SVI enabled, and Gi0/1 up and forwarding. Removing that last member can take the SVI protocol down while configuration remains.
Pause and explain it in your own words
Would shutting one access port always take its SVI down?
Show a hint
Consider other access or trunk members carrying that VLAN.
Show the explanation
No. Another eligible up forwarding member can keep the SVI operational. The lab deliberately has only one VLAN 20 member so the dependency is unambiguous.
Short answer
What should you understand today?
An SVI is a VLAN's logical IP interface; a routed physical port has its IP address directly on the port. A capable switch with IP routing enabled can forward between these interfaces. An SVI also needs a working Layer 2 VLAN attachment: its address can remain configured while its operational state and connected route disappear.
Before you begin
Learning targets
- Understand VLAN membership, IPv4 gateways and the router-on-a-stick lesson.
- Use fresh entitled CML 2.10 IOSvL2 and IOSv nodes with exact image builds recorded.
- Know Console modes and do not attach this exercise to a shared network.
- Compare a switchport, SVI and routed physical interface.
- Enable inter-VLAN routing on a supported virtual switch.
- Verify SVI autostate prerequisites and connected routes.
- Read relevant interface events without inventing logs or timestamps.
- Restore the last active VLAN member and repeat the same endpoint test.
Words you will meet
Open a word when you need its meaning. You do not need to memorize the whole list before reading.
Layer 2 switchport
A switchport forwards Ethernet frames within VLANs. An access port belongs to one ordinary data VLAN; an 802.1Q trunk can carry multiple VLANs.
SVI
A switched virtual interface gives a switch a logical IP attachment to one VLAN. On a routing-capable switch it can be that VLAN's gateway; merely creating it does not enable transit routing.
Routed physical port
A physical interface configured with no switchport becomes a Layer 3 port with an IP address on the port itself. It is not an access member or a trunk for the old VLAN.
IP routing
IP routing enables packet forwarding between IP interfaces on a capable switch. A management-only default gateway setting is not a replacement for routing configuration.
Autostate
Normal SVI operational state depends on an active VLAN, an enabled SVI and at least one eligible up Layer 2 member in forwarding state. Platform exceptions exist; this lesson uses the normal IOSvL2 model.
Connected route
An operational addressed IP interface supplies a connected network route. The route can disappear when the interface's protocol goes down even though the address remains in configuration.
Syslog
Syslog records device events. A message has a facility, severity and mnemonic plus descriptive content. A recorded state transition is evidence of an event, not automatic proof of its root cause.
Console and control test
Console is direct management of the named node. A control test follows an unaffected path during the fault, helping distinguish selective VLAN failure from complete device failure.
Three interface types serve different purposes
A Layer 2 access port associates endpoint frames with a VLAN. An SVI is the switch's logical IP attachment to that VLAN. A routed physical port removes switchport behavior and places an IP network directly on the physical interface. These can coexist on a routing-capable switch without making them interchangeable.
- Check show interfaces switchport to distinguish Layer 2 from routed behavior.
- Do not run no switchport on an existing user trunk or shared access port.
Enable routing but preserve VLAN boundaries
With operational SVIs and IP routing enabled, the switch can route packets between the attached prefixes. Endpoints use their local SVI as the next hop for off-subnet destinations. The VLANs remain separate Layer 2 broadcast domains even though an authorized routed path now exists between them.
- A management default gateway command is not a substitute for transit IP routing.
- No static route is needed between these two directly connected operational SVIs.
An SVI has Layer 2 dependencies
Normal autostate considers VLAN existence and active state, administrative enablement and at least one eligible up forwarding Layer 2 member. The SVI's configured address can remain when those prerequisites fail. Do not defeat this dependency to make a status display look healthy; investigate the real member path.
- Record both status and protocol columns; exact down wording can vary by platform.
- Wait for forwarding convergence before concluding an enabled port did not restore the SVI.
A routed uplink is not another VLAN trunk
Gi0/2 uses a /30 network directly toward R2. It does not carry VLAN 10 or 20 tags and does not count as a Layer 2 member keeping their SVIs up. Its successful peer ping provides a control during the VLAN 20 fault, but the lab deliberately does not provide R2 with routes to the user VLANs.
- The routed cable has its own subnet and no access VLAN assignment.
- A local link test cannot establish a remote routing service.
Correlate events, state and traffic
Read show logging together with interface state and connected routes. A LINK or LINEPROTO event can identify an interface transition, but it does not prove which person, cable or policy caused it. Preserve exact messages if present, including timestamps and clock uncertainty. An empty buffer is not proof that no transition happened.
- Never invent exact timestamps, message counts or recovery durations.
- This covers relevant logs for v2.0 2.4; comprehensive syslog treatment belongs later.
Real-world walkthrough
The gateway address exists, but the gateway is not operational
A hypothetical administrator sees Vlan20's address in running configuration and assumes the gateway must work. The VLAN's last active access cable was disconnected. Re-entering the same IP address changes no missing dependency and can distract from the actual interface evidence.
- Compare the configured SVI address with its actual status and protocol columns.
- Check VLAN existence and list every access or trunk member that could keep the SVI active.
- Inspect the remaining members' link and spanning-tree state and correlate any retained log events.
- Restore the intended member path rather than forcing an artificial SVI-up state.
- Repeat the endpoint gateway and cross-VLAN tests, documenting actual observations and remaining unknowns.
Guided GNS3 lab
SVI autostate beside a separate routed port
Build two routed VLANs and a /30 adjacent routed link. Shut only VLAN 20's last member, observe logical dependencies and restore it. Runtime, event timing and physical hardware behavior remain unmeasured by the author.
Addressing plan
| Device | Interface | Address | Purpose |
|---|---|---|---|
| SW1 | Vlan10 | 192.0.2.1/24 | H1 gateway |
| SW1 | Vlan20 | 198.51.100.1/24 | H2 gateway |
| H1 | Gi0/0 | 192.0.2.10/24; gateway 192.0.2.1 | VLAN10 endpoint |
| H2 | Gi0/0 | 198.51.100.20/24; gateway 198.51.100.1 | VLAN20 endpoint |
| SW1 | Gi0/2 | 203.0.113.1/30 | Direct routed control link |
| R2 | Gi0/0 | 203.0.113.2/30 | Adjacent control peer only |
Set up the lab
- Build a fresh four-node CML 2.10 project under existing entitlement and record exact image builds. No external connectors or production interfaces.
- Create only the three listed cables; preserve the original lab. Decline initial configuration dialogs if offered.
- Verify Console access to each node and stop if the selected platform lacks routed-port or SVI forwarding support.
- Paper alternative: complete a dependency table for VLAN existence, member state, SVI state and connected route. It does not establish practical runtime competence.
Create VLANs and preserve baseline
In CML, select SW1, open its Console tab and connect before typing. Inspect the switch and its existing log-buffer settings before changing this fresh lab. Keep any pre-existing output in private notes.
enable
show version
show logging
configure terminal
vlan 10
exit
vlan 20
endWhat each command means
enable- Enter privileged EXEC on the named lab node; stop if authorization is unavailable.
show version- Record the image that must support routed ports and SVIs.
show logging- Read existing events and buffer settings without clearing evidence.
configure terminal- Enter global configuration mode from privileged EXEC; changes apply as accepted.
vlan 10- Create H1's broadcast domain.
exit- Return to global configuration.
vlan 20- Create H2's broadcast domain.
end- Return to privileged EXEC without saving or reversing the configuration.
- What you should see
- VLANs 10 and 20 exist; baseline state and any existing logs are recorded.
- Why this step matters
- Later events need starting context, and missing historical logs must be reported honestly.
Configure the two Layer 2 access ports
In CML, select SW1, open its Console tab and connect before typing. Gi0/0 and Gi0/1 are endpoint access links, not routed ports. VLAN 20 must have no other active member for the fault experiment.
configure terminal
interface GigabitEthernet0/0
switchport mode access
switchport access vlan 10
no shutdown
exit
interface GigabitEthernet0/1
switchport mode access
switchport access vlan 20
no shutdown
endWhat each command means
configure terminal- Enter global configuration mode from privileged EXEC; changes apply as accepted.
interface GigabitEthernet0/0- Select H1's physical access cable.
switchport mode access- Keep H1's port in Layer 2 access mode.
switchport access vlan 10- Place H1 in VLAN 10.
no shutdown- Enable H1's cable interface.
exit- Return to global interface selection.
interface GigabitEthernet0/1- Select H2's physical access cable.
switchport mode access- Keep H2's port in Layer 2 access mode.
switchport access vlan 20- Make this the sole VLAN 20 member.
no shutdown- Enable H2's cable interface.
end- Return to privileged EXEC without saving or reversing the configuration.
- What you should see
- The two ports are assigned to distinct local domains.
- Why this step matters
- The SVI needs Layer 2 membership, while endpoint off-subnet traffic needs the later gateway configuration.
Create gateway SVIs and enable routing
In CML, select SW1, open its Console tab and connect before typing. Assign unique gateway addresses to logical VLAN interfaces. Do not put those gateway addresses directly on the access ports.
configure terminal
ip routing
interface Vlan10
ip address 192.0.2.1 255.255.255.0
no shutdown
exit
interface Vlan20
ip address 198.51.100.1 255.255.255.0
no shutdown
endWhat each command means
configure terminal- Enter global configuration mode from privileged EXEC; changes apply as accepted.
ip routing- Enable transit IP routing on this supported virtual switch.
interface Vlan10- Select the logical VLAN 10 IP attachment.
ip address 192.0.2.1 255.255.255.0- Assign H1's local gateway address.
no shutdown- Enable the VLAN 10 SVI administratively.
exit- Return to global configuration.
interface Vlan20- Select the logical VLAN 20 IP attachment.
ip address 198.51.100.1 255.255.255.0- Assign H2's local gateway address.
no shutdown- Enable the VLAN 20 SVI administratively.
end- Return to privileged EXEC without saving or reversing the configuration.
- What you should see
- SVI addresses exist; operational state still depends on their member links.
- Why this step matters
- Routing permission and usable VLAN attachment are two separate prerequisites.
Configure a Layer 3 physical link
In CML, select SW1, open its Console tab and connect before typing. Gi0/2 is fresh and reserved for R2. Converting an existing user port could remove service, so never apply this block to an unrelated interface.
configure terminal
interface GigabitEthernet0/2
no switchport
ip address 203.0.113.1 255.255.255.252
no shutdown
end
show interfaces GigabitEthernet0/2 switchportWhat each command means
configure terminal- Enter global configuration mode from privileged EXEC; changes apply as accepted.
interface GigabitEthernet0/2- Select the dedicated R2 cable.
no switchport- Convert this fresh port to routed physical-interface behavior.
ip address 203.0.113.1 255.255.255.252- Assign the .1 endpoint of the /30 routed network.
no shutdown- Enable the dedicated routed link.
end- Return to privileged EXEC without saving or reversing the configuration.
show interfaces GigabitEthernet0/2 switchport- Verify switchport behavior is disabled.
- What you should see
- Gi0/2 is routed rather than an access/trunk member.
- Why this step matters
- This direct link must not be mistaken for a Layer 2 VLAN member supporting SVI autostate.
Address the routed control peer
In CML, select R2, open its Console tab and connect before typing. Configure only R2's adjacent /30 interface. No default or user-VLAN route is needed for this two-endpoint control test.
enable
configure terminal
interface GigabitEthernet0/0
ip address 203.0.113.2 255.255.255.252
no shutdown
endWhat each command means
enable- Enter privileged EXEC on the named lab node; stop if authorization is unavailable.
configure terminal- Enter global configuration mode from privileged EXEC; changes apply as accepted.
interface GigabitEthernet0/0- Select the cable to SW1's routed Gi0/2.
ip address 203.0.113.2 255.255.255.252- Assign the distinct peer address in the /30.
no shutdown- Enable R2's adjacent interface.
end- Return to privileged EXEC without saving or reversing the configuration.
- What you should see
- R2 can become reachable from SW1 on the directly connected /30.
- Why this step matters
- No claim of H1-to-R2 service is made because that requires a separately configured return route.
Configure H1 routed test endpoint
In CML, select H1, open its Console tab and connect before typing. Use this IOSv node's single data interface. Its explicit default route stands in for a desktop's local gateway configuration.
enable
configure terminal
interface GigabitEthernet0/0
ip address 192.0.2.10 255.255.255.0
no shutdown
exit
ip route 0.0.0.0 0.0.0.0 192.0.2.1
endWhat each command means
enable- Enter privileged EXEC on the named lab node; stop if authorization is unavailable.
configure terminal- Enter global configuration mode from privileged EXEC; changes apply as accepted.
interface GigabitEthernet0/0- Select this endpoint's mapped access cable.
ip address 192.0.2.10 255.255.255.0- Set the endpoint's unique address and local /24 prefix.
no shutdown- Enable the endpoint interface.
exit- Return to global mode to configure the next hop.
ip route 0.0.0.0 0.0.0.0 192.0.2.1- Use the local SVI address for off-subnet destinations.
end- Return to privileged EXEC without saving or reversing the configuration.
- What you should see
- The endpoint has its planned local address and off-subnet next hop.
- Why this step matters
- Both endpoint return paths are needed to validate inter-VLAN echo exchanges.
Configure H2 routed test endpoint
In CML, select H2, open its Console tab and connect before typing. Use this IOSv node's single data interface. Its explicit default route stands in for a desktop's local gateway configuration.
enable
configure terminal
interface GigabitEthernet0/0
ip address 198.51.100.20 255.255.255.0
no shutdown
exit
ip route 0.0.0.0 0.0.0.0 198.51.100.1
endWhat each command means
enable- Enter privileged EXEC on the named lab node; stop if authorization is unavailable.
configure terminal- Enter global configuration mode from privileged EXEC; changes apply as accepted.
interface GigabitEthernet0/0- Select this endpoint's mapped access cable.
ip address 198.51.100.20 255.255.255.0- Set the endpoint's unique address and local /24 prefix.
no shutdown- Enable the endpoint interface.
exit- Return to global mode to configure the next hop.
ip route 0.0.0.0 0.0.0.0 198.51.100.1- Use the local SVI address for off-subnet destinations.
end- Return to privileged EXEC without saving or reversing the configuration.
- What you should see
- The endpoint has its planned local address and off-subnet next hop.
- Why this step matters
- Both endpoint return paths are needed to validate inter-VLAN echo exchanges.
Baseline the local and remote gateway paths
In CML, select H1, open its Console tab and connect before typing. Wait for member forwarding state and discovery. Both tests must work before the controlled member failure.
ping 192.0.2.1
ping 198.51.100.20What each command means
ping 192.0.2.1- Test H1's local SVI gateway.
ping 198.51.100.20- Test H2 through SW1's routing function and return path.
- What you should see
- Expect both destinations to reply after normal convergence.
- Why this step matters
- This establishes the behavior that the later dependency fault should change.
Record SVI, route and control evidence
In CML, select SW1, open its Console tab and connect before typing. Confirm both SVIs are operational and record VLAN 20 membership. Do not proceed if another active member would invalidate the last-member experiment.
show ip interface brief
show vlan brief
show spanning-tree vlan 20
show ip route connected
ping 203.0.113.2
show loggingWhat each command means
show ip interface brief- Record both SVI and routed physical-port states.
show vlan brief- Confirm Gi0/1 is the only VLAN 20 access member.
show spanning-tree vlan 20- Check the member is forwarding for VLAN 20.
show ip route connected- Record all three connected networks.
ping 203.0.113.2- Establish the separate routed-link control test.
show logging- Preserve baseline events without clearing the buffer.
- What you should see
- Expect operational SVIs, their connected networks and a replying routed peer.
- Why this step matters
- Each observation answers a different prerequisite or control question.
Remove the last VLAN 20 member
In CML, select SW1, open its Console tab and connect before typing. Disable only Gi0/1 and leave Vlan20's address and administrative setting unchanged. Do not save the fault or force the SVI state.
configure terminal
interface GigabitEthernet0/1
shutdown
end
show ip interface brief
show ip route connected
show logging
ping 203.0.113.2What each command means
configure terminal- Enter global configuration mode from privileged EXEC; changes apply as accepted.
interface GigabitEthernet0/1- Select the sole H2 access member.
shutdown- Disable that member's link administratively.
end- Return to privileged EXEC without saving or reversing the configuration.
show ip interface brief- Observe Vlan20 protocol and Gi0/1 administrative state.
show ip route connected- Check the VLAN 20 connected route is withdrawn under normal autostate.
show logging- Record actual member/SVI transition messages if retained.
ping 203.0.113.2- Check the independent routed peer remains reachable.
- What you should see
- Expect Vlan20 to lose operational state while its IP configuration remains; the routed control link should still reply.
- Why this step matters
- Removing a Layer 2 dependency can remove a Layer 3 route without deleting the configured address.
Observe the selective endpoint failure
In CML, select H1, open its Console tab and connect before typing. Repeat both baseline tests. Keep H1's own address and gateway fixed throughout the experiment.
ping 192.0.2.1
ping 198.51.100.20What each command means
ping 192.0.2.1- Check the unaffected local VLAN 10 gateway.
ping 198.51.100.20- Test the now-disconnected VLAN 20 endpoint.
- What you should see
- Expect the local gateway to reply and H2's exchange to fail.
- Why this step matters
- The test confirms user-visible impact, while interface and route evidence explain this controlled cause.
Restore and inspect the dependency
In CML, select SW1, open its Console tab and connect before typing. Re-enable only Gi0/1, wait for normal forwarding convergence and inspect the same logical state and events.
configure terminal
interface GigabitEthernet0/1
no shutdown
end
show ip interface brief
show ip route connected
show loggingWhat each command means
configure terminal- Enter global configuration mode from privileged EXEC; changes apply as accepted.
interface GigabitEthernet0/1- Select the exact member disabled by the experiment.
no shutdown- Restore the member's enabled baseline.
end- Return to privileged EXEC without saving or reversing the configuration.
show ip interface brief- Check Vlan20 returns to operational state after convergence.
show ip route connected- Confirm its connected network is installed again.
show logging- Retain actual recovery events and note clock uncertainty.
- What you should see
- Expect member, SVI and route recovery without changing gateway addresses.
- Why this step matters
- The correct inverse restores the missing dependency rather than hiding its state.
Repeat the original verification
In CML, select H1, open its Console tab and connect before typing. After member convergence, repeat the exact tests and preserve results. Stop if recovery differs from the baseline.
ping 192.0.2.1
ping 198.51.100.20What each command means
ping 192.0.2.1- Recheck the local gateway control.
ping 198.51.100.20- Recheck the full inter-VLAN endpoint exchange.
- What you should see
- Expect both baseline destinations to reply again.
- Why this step matters
- A route entry returning is supporting evidence; the peer test closes the selected user path.
Verify
- Confirm access ports stay Layer 2 while Gi0/2 has switchport disabled.
- Verify both SVIs, ip routing and endpoint gateway choices.
- Require a successful endpoint baseline and direct routed-link control.
- Correlate the last-member fault with actual SVI, route and available log changes.
- Restore membership, await forwarding and repeat the original endpoint exchange.
Troubleshoot
- If an SVI remains down, check VLAN existence, administrative state and all eligible member links before changing its address.
- If one member is disabled but the SVI remains up, look for another forwarding access/trunk member; do not fabricate the expected down state.
- If inter-VLAN traffic fails with SVIs up, inspect ip routing, masks and endpoint return gateways. No ACL is intended in this clean lab.
- If logs are missing or clocks disagree, record that limitation. State transitions alone do not prove a physical cable defect or identify an operator.
Use an existing Cisco Modeling Labs 2.10 entitlement and its bundled reference images inside CML only. GNS3 does not provide Cisco images; use images there only when a separate applicable license permits that environment. Do not share or redistribute image files. A CML subscription alone does not authorize exporting its Cisco images to GNS3. Without entitlement, use the explicitly labeled paper exercises; they do not establish hands-on competence.
- Restore Gi0/1 and verify both endpoint tests; do not leave the sole VLAN 20 member disabled.
- Preserve actual logs privately, then stop the isolated nodes. Do not erase logs, delete VLANs or modify unrelated routed interfaces.
Practice set
Answer before you reveal
01Where does a VLAN gateway address belong?
The access port supplies VLAN membership while the logical interface supplies the VLAN's IP attachment.
02What does no switchport change?
That removes its ordinary access/trunk behavior; applying it blindly can change the network design.
03Why can an SVI address exist without a connected route?
Normal route installation depends on operational attachment, not merely a saved address line.
04What keeps an SVI up after one member fails?
The last-member condition is deliberately controlled in this lab; a larger VLAN can have multiple paths.
05Does SW1-to-R2 ping prove H1-to-R2 reachability?
The control test covers only the directly connected /30 endpoints, not user-VLAN transit.
06What does a log transition prove by itself?
Correlate time, configuration, interface evidence and tests before attributing a failure to a person or physical component.
Knowledge check
Quiz: prove the reasoning
Keep these
Technical takeaways
- Switchports, SVIs and routed ports have different roles.
- Operational SVI attachment depends on eligible Layer 2 membership.
- IP routing and endpoint return paths are separate prerequisites.
- Connected routes follow operational state, not address text alone.
- Use real log content and acknowledge missing or uncertain timestamps.
- Retest the original endpoint path after restoring the exact failed dependency.