eigrp stub connected summary
Configures an EIGRP stub router to advertise only connected and summary routes, preventing it from being used as a transit router and reducing query scope.
Definition: eigrp stub connected summary is a Cisco IOS router config command. Configures an EIGRP stub router to advertise only connected and summary routes, preventing it from being used as a transit router and reducing query scope.
Overview
The `eigrp stub connected summary` command is a critical tool for optimizing EIGRP networks by designating a router as a stub. A stub router is one that is not intended to be used as a transit path for traffic between other routers; it typically has only one or a few connections to the rest of the network. By configuring a router as a stub, you instruct it to advertise only specific types of routes—in this case, connected and summary routes—and to suppress the advertisement of other routes learned via EIGRP.
This reduces the query scope during network convergence, as stub routers are not queried for alternate paths, thereby speeding up convergence and reducing control plane overhead. The command is particularly useful in hub-and-spoke topologies, where spoke routers are stub routers that should not be used for transit traffic. Without this command, a spoke router might be queried for routes it does not have, causing unnecessary delays and resource consumption.
The `eigrp stub` command has several options: `connected`, `static`, `summary`, `redistributed`, and `receive-only`. The `connected summary` combination is common for spokes that only need to advertise their directly connected networks and any summary routes configured on them. This command is configured in router configuration mode under the EIGRP process.
It is important to note that the `eigrp stub` command affects the router's behavior immediately; the router will stop advertising non-stub routes and will not be used as a transit router. The command is available in IOS versions 12.0 and later, and it is a fundamental concept for CCNP-level EIGRP knowledge. When troubleshooting, verifying the stub configuration with `show ip eigrp neighbors detail` or `show ip eigrp topology` can reveal whether the stub setting is properly limiting route advertisements.
The command does not require any special privilege level beyond enable mode, and it is saved in the running configuration. Understanding this command is essential for designing scalable EIGRP networks that minimize convergence time and control plane load.
eigrp stub connected summaryWhen to Use This Command
- Configuring a remote branch router that should only advertise its directly connected networks and any summary routes, not participate in full EIGRP routing.
- Limiting the routing table size on a spoke router in a hub-and-spoke topology by suppressing all other route advertisements.
- Preventing a low-end router from being used as a transit router for EIGRP traffic, reducing CPU and memory load.
- Controlling which routes are advertised from a stub router to the hub, ensuring only necessary prefixes are sent.
Parameters
| Parameter | Syntax | Description |
|---|---|---|
| connected | connected | Instructs the stub router to advertise only connected routes that are learned via EIGRP. This is commonly used to limit the routes advertised by a spoke router to its directly attached networks. |
| summary | summary | Allows the stub router to advertise summary routes that have been configured manually via the `ip summary-address eigrp` command. This is useful when the stub router aggregates its connected networks into a summary route. |
Command Examples
Basic stub configuration with connected and summary
router eigrp 100
eigrp stub connected summaryR1(config-router)#router eigrp 100 R1(config-router)#eigrp stub connected summary %DUAL-5-NBRCHANGE: EIGRP-IPv4 100: Neighbor 10.0.0.2 (GigabitEthernet0/0) is up: new adjacency R1(config-router)#
The command enables EIGRP stub mode for process 100, advertising only connected and summary routes. The output shows a neighbor adjacency reset and re-establishment, confirming the stub configuration took effect.
Verifying stub configuration
show ip eigrp neighbors detailEIGRP-IPv4 Neighbors for AS(100)
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) Cnt Num
0 10.0.0.2 Gi0/0 13 00:12:34 1 200 0 45
Version 12.0/2.0, Retrans: 0, Retries: 0, Prefixes: 3
Topology-ids from peer - 0
Stub Peer Advertising (CONNECTED SUMMARY) Routes
Suppressing queriesThe 'Stub Peer Advertising (CONNECTED SUMMARY) Routes' line confirms the neighbor is a stub router advertising only connected and summary routes. 'Suppressing queries' indicates the hub will not send queries to this neighbor, reducing query scope.
Understanding the Output
The 'show ip eigrp neighbors detail' output reveals stub status. Look for 'Stub Peer Advertising' followed by the route types (CONNECTED, SUMMARY, etc.). If you see 'Suppressing queries', the stub router will not receive EIGRP queries, which is expected.
A missing 'Stub Peer' line means the router is not configured as a stub. In 'show ip eigrp topology', stub routers will only have entries for their own connected and summary routes; they will not learn external routes. Good values: stub routers have small routing tables and low CPU.
Bad values: if a stub router shows many routes, it may be misconfigured or leaking routes. Watch for 'eigrp stub' without keywords, which defaults to connected and summary only.
Configuration Scenarios
Configure a spoke router in a hub-and-spoke topology to advertise only its connected networks and a summary route
In a hub-and-spoke EIGRP network, the spoke router (R2) has multiple connected subnets (192.168.1.0/24, 192.168.2.0/24) and a summary route (192.168.0.0/22) configured. The hub router (R1) should not use R2 as a transit router. The goal is to configure R2 as a stub router that advertises only its connected and summary routes.
Topology
R1(Gi0/0)---10.0.12.0/30---(Gi0/0)R2
R2 has LAN subnets: 192.168.1.0/24, 192.168.2.0/24Steps
- 1.Step 1: Enter global configuration mode on R2: R2> enable; R2# configure terminal
- 2.Step 2: Enter EIGRP router configuration mode for AS 100: R2(config)# router eigrp 100
- 3.Step 3: Configure the stub router to advertise connected and summary routes: R2(config-router)# eigrp stub connected summary
- 4.Step 4: (Optional) Configure a summary route on R2: R2(config-router)# interface gi0/0; R2(config-if)# ip summary-address eigrp 100 192.168.0.0 255.255.252.0
- 5.Step 5: Exit configuration mode and save: R2(config-if)# end; R2# copy running-config startup-config
! Full IOS config block R2# configure terminal R2(config)# router eigrp 100 R2(config-router)# eigrp stub connected summary R2(config-router)# exit R2(config)# interface gi0/0 R2(config-if)# ip summary-address eigrp 100 192.168.0.0 255.255.252.0 R2(config-if)# end
Verify: Use `show ip eigrp neighbors detail` on R2 to verify the stub status. Expected output includes 'Stub Peer Advertising (CONNECTED SUMMARY)' in the neighbor details. Also use `show ip eigrp topology` on R1 to confirm that only the connected and summary routes from R2 are present.
Watch out: A common mistake is forgetting to configure the summary route on the interface before using the `summary` keyword. Without a configured summary address, the `summary` keyword has no effect. Also, ensure that the stub router is not configured with `redistribute` or `static` if not intended, as those would also be advertised.
Convert an existing spoke router from a transit router to a stub router to improve convergence
An existing EIGRP network has a spoke router (R3) that is currently acting as a transit router, causing slow convergence due to query propagation. The network engineer wants to restrict R3 to advertise only its connected routes and any summary routes, preventing it from being queried for alternate paths.
Topology
R1(Gi0/0)---10.0.13.0/30---(Gi0/0)R3---(Gi0/1)---10.0.34.0/30---R4
R3 has LAN: 172.16.1.0/24Steps
- 1.Step 1: Enter global configuration mode on R3: R3> enable; R3# configure terminal
- 2.Step 2: Enter EIGRP router configuration mode: R3(config)# router eigrp 100
- 3.Step 3: Apply the stub configuration: R3(config-router)# eigrp stub connected summary
- 4.Step 4: Verify that R3 no longer advertises routes learned from R4 (e.g., 10.0.34.0/30) to R1: R3(config-router)# end
- 5.Step 5: Save configuration: R3# copy running-config startup-config
! Full IOS config block R3# configure terminal R3(config)# router eigrp 100 R3(config-router)# eigrp stub connected summary R3(config-router)# end R3# copy running-config startup-config
Verify: On R1, use `show ip eigrp topology` to confirm that routes from R3 are limited to connected and summary routes. On R3, use `show ip eigrp neighbors detail` to see 'Stub Peer Advertising (CONNECTED SUMMARY)'. Also, use `debug eigrp packets query` on R1 to ensure no queries are sent to R3 after the change.
Watch out: If R3 was previously redistributing routes or had static routes, those will no longer be advertised unless the `redistributed` or `static` keywords are also included. Ensure that the stub configuration matches the desired route advertisement policy. Also, note that the stub configuration takes effect immediately, which may cause temporary route loss if not planned.
Troubleshooting with This Command
When troubleshooting EIGRP stub configurations, the primary tool is `show ip eigrp neighbors detail`. This command displays the stub status of each neighbor, including which route types are advertised. A healthy output for a stub router configured with `connected summary` will show 'Stub Peer Advertising (CONNECTED SUMMARY)'.
If the output shows 'Stub Peer Advertising (NONE)' or 'Stub Peer Advertising (ALL)', the configuration may be incorrect or incomplete. Another key command is `show ip eigrp topology` on the hub router to verify that only expected routes are received from the stub. If unexpected routes appear (e.g., routes learned via redistribution), the stub router may have additional route sources not covered by the stub keywords.
Common symptoms that this command helps diagnose include: slow convergence in hub-and-spoke networks, excessive query traffic, or routes appearing on the hub that should not be there. A step-by-step diagnostic flow would be: 1) On the hub router, use `show ip eigrp neighbors` to list neighbors and their interfaces. 2) For each spoke neighbor, use `show ip eigrp neighbors detail` to check the stub status. 3) If a spoke is not showing as stub, verify the configuration on the spoke router. 4) Use `show ip eigrp topology` on the hub to see the routes learned from each neighbor. 5) If a spoke is advertising more routes than expected, check for redistribution or static routes on the spoke. 6) Use `debug eigrp packets` on the hub to see the types of packets exchanged (queries, replies, updates). A stub router should not send queries; if it does, the stub configuration may be missing or misapplied.
Correlating with `show ip route eigrp` can help identify which routes are being learned from which neighbor. For example, if a spoke router is advertising a route that is not connected or summary, it may be redistributing a static route without the `static` keyword in the stub command. In such cases, add the `static` keyword or remove the redistribution.
Another common issue is that the stub router may have multiple EIGRP processes; ensure the stub command is applied to the correct process. Finally, remember that the `eigrp stub` command only affects routes learned via EIGRP; it does not affect directly connected routes or summary routes that are configured on interfaces. If a summary route is not being advertised, verify that the `ip summary-address eigrp` command is configured on the correct interface and that the summary route exists in the routing table.
CCNA Exam Tips
CCNA exam tip: The 'eigrp stub' command defaults to 'connected' and 'summary' if no keywords are specified.
CCNA exam tip: Stub routers reduce query scope and prevent transit traffic; they are commonly used at branch sites.
CCNA exam tip: The 'receive-only' keyword prevents the stub from advertising any routes, useful for pure leaf nodes.
CCNA exam tip: Remember that stub routers do not form neighbor relationships with other stub routers; they only connect to hub routers.
Common Mistakes
Mistake 1: Forgetting to include 'connected' or 'summary' keywords, causing the stub to advertise only default routes (if configured) or nothing.
Mistake 2: Configuring 'eigrp stub' on a hub router, which can break routing because the hub will not advertise routes to other spokes.
Mistake 3: Using 'eigrp stub' without understanding that it suppresses queries; if the stub has a backup link to another stub, queries may be lost.
eigrp stub connected summary vs show ip eigrp topology
These EIGRP commands are often considered together because both relate to how routes are advertised and viewed in an EIGRP network, yet they operate at different layers: one configures stub behavior to limit route advertisement, while the other displays the topology table for verification.
| Aspect | eigrp stub connected summary | show ip eigrp topology |
|---|---|---|
| Scope | Limits routes advertised by stub router | Displays all learned EIGRP routes |
| Configuration mode | Router config | Privileged EXEC |
| Persistence | Persistent in running config | Non-persistent, runtime output only |
| Effect on network | Reduces query range, prevents transit traffic | No effect; used for diagnostics |
| Typical use | Configure spoke router in hub-and-spoke | Verify EIGRP convergence and path selection |
Use eigrp stub connected summary when you need to configure a branch router to prevent it from being a transit router and to reduce query scope.
Use show ip eigrp topology when you need to verify the EIGRP topology table, check feasible successors, or troubleshoot route convergence.
Platform Notes
In IOS-XE (e.g., Catalyst 9000 switches), the `eigrp stub` command syntax is identical to classic IOS. However, the output format of `show ip eigrp neighbors detail` may differ slightly, but the key fields remain the same. In NX-OS (e.g., Nexus switches), EIGRP is not supported; the equivalent concept for stub routing is achieved using route maps or prefix lists to filter advertisements, or by using the `stub` feature in OSPF if OSPF is used instead.
For ASA firewalls, EIGRP is not supported; the ASA uses routing protocols like OSPF or RIP, and stub routing is configured differently (e.g., OSPF stub area). In IOS-XR, EIGRP is not supported; the platform uses OSPF or IS-IS. The command `eigrp stub` is available in IOS versions 12.0(7)T and later.
In IOS 15.x and 16.x, the command remains unchanged. One notable behavior difference is that in older IOS versions (12.x), the `eigrp stub` command required the router to have at least one `network` statement under the EIGRP process; otherwise, the command would be rejected. In newer versions, this restriction is relaxed.
Additionally, in IOS 15.x, the `eigrp stub` command can be applied to named EIGRP configurations as well. Always verify the specific IOS version documentation for any nuances.
Related Commands
show ip eigrp neighbors
Displays all EIGRP neighbours with their addresses, interfaces, hold time, uptime, SRTT (smooth round-trip time), RTO, queue count, and sequence numbers.
show ip eigrp topology
Displays the EIGRP topology table, showing all learned routes and their feasible successors, used to verify EIGRP convergence and path selection.
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