Configuring EIGRP Stub’s
EIGRP Stubs can be extremely useful when building a scalable EIGRP Routed network. This lab will discuss and demonstrate the configuration and verification of EIGRP Stubs.
Real World Application & Core Knowledge
The more routers you have the more queries you have and the more queries and latency you have the greater the chance routers in your network will become SIA (Stuck in Active), in which case any neighboring EIGRP nodes that does not return a query reply in the specified thread hold will be dropped and any routes learned via that neighbor will be also removed from the routing table even if the routes were up. So in a worst case scenario, such problems can result in your routing table automagically disappearing…
With all of this information brought to the table; does R5 really need to be queried regarding networks upstream when it only has one point of entry into the network? That’s a definite no. So R5 becomes a prime candidate to become a stub eigrp router in which case will receive all routes but only advertise connected and summary routes upstream.
When a router has formed a stub neighbor adjacency with another router, the stub eigrp neighbor will not be sent any queries so this effectively speeds up network convergence as now there’s one less router to query in case of a route failure.
There are seven different types of EIGRP stubs but the CCNA scope only coves the basic stub which is will receive all EIGRP routes but send only connected and summary routes. The list compiled below shows the different types of stub networks that eigrp can be configured as;
| Command | Description |
|---|---|
| EIGRP Stub | This is the default stub configuration if additional syntax is not specified such as the following listed below; the default stub will send both connected and summary routes and receive all routes from upstream neighbors. |
| EIGRP Stub Connected | Configures a router as a stub router that advertises only directly connected routes. This type of stub can be used in conjecture with the other stub types excluding receive-only. |
| EIGRP Stub Leak-Map | Configures a router as a stub router that advertises only route prefixes that match a specific ip prefix-list. |
| EIGRP Stub Receive-Only | Configures an EIGRP router as a stub router that will ONLY receive routes from upstream and not advertise any routes to its neighboring routers. When using this stub type; static routes must be configured upstream to reach networks within this stub area. |
| EIGRP Stub Redistribute | Configures an EIGRP router as a stub router that will only advertise redistributed routes. This type of stub can be used in conjecture with the other stub types excluding receive-only. |
| EIGRP Stub Static | Configures an EIGRP router as a stub router that will only advertise static routes. This type of stub can be used in conjecture with the other stub types excluding receive-only. |
| EIGRP Stub Summary | Configures an EIGRP router as a stub router that will only advertise summary routes. This type of stub can be used in conjecture with the other stub types excluding receive-only. |
The CCNA exam objectives only requires you to be familiar with the basic EIGRP stub operation however if you wish to further your knowledge you may experiment with the other EIGRP stub types.
To configure the EIGRP stub type navigate to the EIGRP router process configuration mode then use the eigrp stub command.
You can verify which neighbors are stub neighbors by using the show ip eigrp neighbors detail command in privileged mode.
In this lab R5 is a branch office and R4 is a regional office. R5 only has a single network it routes for which is 10.80.50.0/24. You will configure R5 as an EIGRP stub router and verify your configuration.
Familiarize yourself with the following new command(s);
| Command | Description |
|---|---|
| eigrp stub {receive-only | connected | static | summary | redistribute | leak-map} | This command is executed in the EIGRP routing process configuration mode to specify a router as a stub router. The default configuration will send directly connected routes and summary routes and receive all routes via an upstream neighbor. You can however specify additional stub configuration following the command such as static or redistribute. |
| show ip eigrp neighbors detail | This command is executed in privileged mode to display which eigrp neighbors are stub routers. EIGRP stub neighbors will not be queried during EIGRP re-convergence. |
This lab will continue to build upon the topology previously used in Lab 8-3 as shown below and other labs found through out Section 8.
Lab Prerequisites
- If you are using GNS3 than load the Free CCNA Workbook GNS3 topology than start devices; R1, R2, R3, R4 and R5.
- Establish a console session with devices R1, R2, R3, R4 and R5 than load the initial configurations provided below by copying the config from the textbox and pasting it into the respected routers console.
Lab Objectives
- Configure R5 as an EIGRP stub network to send connected and summary routes only to its neighboring router(s)
- Verify R5’s EIGRP stub router configuration using only R4.
Lab Instruction
Objective 1. – Configure R5 as an EIGRP stub network to send connected and summary routes only to its neighboring router(s).
There are two different commands you can use to accomplish this objective which do the exact same thing. The first one being eigrp stub which is the default eigrp stub type and will send connected and summary routes or you can use eigrp stub connected summary which will give you the same result. This lab will demonstrate the default eigrp stub type as shown below;
R5>enable R5#configure terminal Enter configuration commands, one per line. End with CNTL/Z. R5(config)#router eigrp 10 R5(config-router)#eigrp stub R5(config-router)#end R5# %SYS-5-CONFIG_I: Configured from console by console %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 10.80.45.1 (Serial0/1) is down: peer info changed R5# %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 10.80.45.1 (Serial0/1) is up: new adjacency R5#
Objective 2. – Verify R5’s EIGRP stub router configuration using only R4.
To view rather or not a neighbor is an EIGRP stub router use the show ip eigrp neighbor detail command in privileged mode as shown below.
R4>show ip eigrp neighbors detail
IP-EIGRP neighbors for process 10
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) Cnt Num
0 10.80.45.2 Se0/1 13 00:05:04 1046 5000 0 55
Version 12.4/1.2, Retrans: 2, Retries: 0, Prefixes: 2
Stub Peer Advertising ( CONNECTED SUMMARY ) Routes
Suppressing queries
1 10.80.234.1 Se0/0 155 00:50:43 126 756 0 71
Static neighbor
Version 12.4/1.2, Retrans: 3, Retries: 0, Prefixes: 11
R4>
As you can see from the output of R4 (10.80.45.2) shown above it is Stub Peer Advertising (CONNECTED SUMMARY ) Routes and below that shows “Suppressing Queries” This verifies that R5 is indeed an EIGRP stub router and that it is advertising only connected and summary routes and will not be queried upon EIGRP network re-convergence.
