EIGRP (Enhanced Interior Gateway Routing Protocol) is a powerful tool that networks use to automatically figure out the best paths for data. The advanced features in this chapter solve two critical problems: how to prevent smaller, less important routers from being overwhelmed with information, and how to efficiently use multiple network connections at the same time for speed and reliability. Mastering EIGRP stub, load balancing, and Named Mode configuration is essential for the 300-410 exam because they represent real-world optimisations that make large enterprise networks stable and fast.
Jump to a section
A simple way to picture Advanced EIGRP Features (Stub, Load Balancing, Named Mode)
When the CEO sends a company-wide memo, the internal mail system delivers it to every department immediately. This creates a lot of unnecessary paper shuffling for smaller regional offices. A large networking setup, like a corporate office, has a similar issue when every router knows about every possible route.
First, the main headquarters (HQ router) in London needs to send all its internal route information to a smaller satellite office router in Manchester. If the Manchester router had to learn about every single sub-department in London, its routing table would be massive and slow. So, you configure the Manchester router as a 'stub' office. A stub office is like a small remote team that only needs to know one thing: the way to the main office. The Manchester stub router only needs a default path back to London; it does not need to know about every individual cubicle in HQ. This makes the Manchester router's job much simpler and prevents it from being overwhelmed with complex route updates.
On the other hand, what if the path between London and Manchester gets jammed? The network, like a good delivery company, can use multiple roads. For example, you have a leased line (direct highway) and a VPN over the internet (back road). Load balancing is the traffic controller that determines whether to send every third parcel down the back road or to split the load 50/50. It makes sure no single road gets totally blocked while the other sits empty, ensuring the memo always arrives as quickly as possible regardless of traffic conditions.
Finally, Named Mode is like the modern email system. In the old days (Classic Mode), you had to send separate, cryptic messages to the mailroom staff for every single tweak. Named Mode lets you define a single, clear policy (like an auto-responder rule) that applies to all traffic at once, making configuration much less messy.
EIGRP (Enhanced Interior Gateway Routing Protocol) is a Cisco proprietary routing protocol. Think of a routing protocol as a language routers use to tell each other where networks are located. EIGRP is special because it is fast and efficient, but it can be chatty. Without advanced features, every router in the network knows about every single network, which can be unnecessary and resource intensive.
EIGRP Stub Router
A stub router is a router that is not supposed to be a transit path. In networking, 'transit' means traffic coming from one part of the network travels through this router to get to another part. A stub router says, 'I am the end of the line. Do not try to send traffic through me to reach other routers.'
Why use a stub? Imagine a small branch office. It has one router connecting to the main office. That router has no reason to know about every single sub-network in the main data centre. By configuring it as a stub, we tell the main office routers to stop sending full routing tables. Instead, the stub router only sends a 'query' for a default route. This reduces memory usage on the cheap branch router and prevents it from being flooded with updates. It also makes the network more stable. If the branch router has a problem, it does not send huge error messages across the whole network.
Stub Router Types
Connected: Advertises only directly connected networks.
Static: Advertises only statically configured routes.
Summary: Advertises only manually summarised routes.
Receive-Only: Advertises nothing; it only listens for routes from the hub.
Leak-Map: A special filter that allows a stub router to advertise a single, specific route even if it is normally blocked by the stub condition.
The key exam point: a stub router, by default, will not forward traffic between two other routers. It is a 'leaf' node, not a 'branch'.
EIGRP Load Balancing
Load balancing is the process of distributing traffic across multiple paths. EIGRP can automatically find multiple paths to the same destination if they exist. This is called 'equal-cost load balancing' when the paths have the same metric (the 'cost' of the path, typically based on bandwidth and delay). EIGRP also supports 'unequal-cost load balancing' using a feature called 'variance'.
The 'variance' command is critical for the exam. It is a multiplier. If you set variance to 2, EIGRP will consider a path that is up to 2 times worse than the best path as a valid path. The router will then split traffic between these paths proportionally to their metric. If one path has a metric of 100 and another has a metric of 120 (within a variance of 2), the router will send more traffic down the better path (100) and less down the 120 path. This maximises the use of available bandwidth.
EIGRP Named Mode
Named Mode is the modern way to configure EIGRP. In the old 'Classic Mode', you had to enter separate commands for the routing process and then separately for each interface. Named Mode organises everything under a single configuration profile called an 'address-family'. This is like having a single policy document for an office rather than a stack of sticky notes on different doors.
Advantages of Named Mode:
It allows you to enable or disable EIGRP on an interface with a single command under the address-family.
It subsumes the configuration for both IPv4 and IPv6 under a single routing process.
It standardises configuration across different Cisco operating systems (IOS, IOS-XE, NX-OS).
It makes route summarisation and stub configuration much cleaner and easier to read.
A named EIGRP configuration starts with:
- router eigrp MY-NAME (creates a named process)
- address-family ipv4 unicast autonomous-system 100 (defines the protocol version and AS number)
- network 10.0.0.0 (advertises the network)
- eigrp stub connected summary (configures the stub behaviour within the address-family)
Named Mode does not change the underlying protocol mechanics; it just changes how you type the configuration. The exam tests you on recognising the correct syntax of Named Mode versus Classic Mode.
Identify the Stub Router Role
Determine which router in your topology is an edge device (like a branch office router) that should not forward traffic between two other routers. This router will become your stub.
Enter EIGRP Named Mode Configuration
Access global configuration mode on the router. Type `router eigrp BRANCH-STUB` to start a named EIGRP process. This is the modern way to configure EIGRP and is heavily tested in the 300-410 exam.
Define the Address-Family
Inside the router configuration, enter `address-family ipv4 unicast autonomous-system 100`. This tells the router you are configuring EIGRP for IPv4 routes under autonomous system 100. All stub and load balancing commands will now be typed inside this block.
Configure the Stub Statement
Inside the address-family, type `eigrp stub connected summary`. This tells the router to operate as a stub, advertising only its directly connected networks and any summarised routes. The exam tests the specific keywords (`connected`, `static`, `summary`, `receive-only`).
Enable Unequal-Cost Load Balancing on the Hub Router
On the hub router (the one the stub talks to), enter the address-family and type `variance 2`. This will allow the hub to use an alternate path up to twice as bad as the best path. If you have a fibre (metric 100) and a DSL (metric 150), both are used because 150 is less than 200 (100 x 2).
Verify Configuration
Use `show ip eigrp neighbors` to confirm the stub router is seen. Use `show ip eigrp topology all-links` on the hub to see if the backup path is now listed as a feasible successor (a valid backup path). Use `show running-config | section router eigrp` to verify the exact commands.
An IT professional working for a retail chain would use these features daily. Consider a company with a headquarters (HQ) in London, three large regional distribution centres (Manchester, Birmingham, Glasgow), and 100 small retail stores.
Step 1: Implementing Stub Routers
Each small retail store has one low-cost router. This router has a single MPLS circuit back to its regional distribution centre. The network engineer configures each store router as an EIGRP stub with the connected and static keywords. Why? Because the store router should only announce its own local networks (like the store Wi-Fi and the cash register network) and the default static route back to the distribution centre. By making it a stub, the distribution centre routers stop sending the entire company routing table to the store. This saves CPU and memory on the store router. It also prevents a configuration mistake at the store router from causing a routing loop (a network traffic jam that never resolves) across the entire company.
Step 2: Configuring Load Balancing
The regional distribution centres, however, have two links to HQ: a high-bandwidth fibre connection and a slower backup DSL line. The engineer wants to use both links all the time, not just during failures. The engineer configures EIGRP on the HQ and distribution centre routers to use unequal-cost load balancing using the variance command. They set the variance to 2. The fibre has a metric of 100, and the DSL has a metric of 180. Since 180 is less than 200 (100 x 2), the DSL link is used. The router automatically sends about twice as much traffic down the fibre as the DSL. This ensures the company gets full value from its backup line, rather than letting it sit idle.
Step 3: Using Named Mode
The company is migrating from older Cisco routers to newer ones. The engineer decides to use EIGRP Named Mode for the new routers. This allows them to write a single configuration template that works for IPv4 (the internal store network) and IPv6 (a future project). The Named Mode configuration looks like this:
router eigrp RETAIL-CORE
address-family ipv4 unicast autonomous-system 100
network 10.0.0.0 0.255.255.255
eigrp stub connected summary
variance 2
The engineer can now copy-paste this configuration to all store routers, changing only the IP addresses. This reduces configuration errors and saves hours of work. The real-world benefit is network stability: a misconfigured store cannot crash the HQ network, and bandwidth costs are minimised because both links are used efficiently.
The 300-410 exam tests your deep understanding of the details, not just the concept. Expect between 3 and 5 questions directly on these topics. The exam loves to trap you with specific command syntax and default behaviours.
What they test:
Stub Router Restrictions: The exam will ask which routes a stub router can advertise by default. The correct answer is that a stub router announces only connected and summary routes (unless you specify 'receive-only' which means it announces nothing). The trap is a distractor option like 'a stub router advertises all routes received from the hub' which is false.
The Leak-Map Feature: This is a high-level exam item. A leak-map is a route-map that permits a specific route to be advertised by a stub router even though stub mode normally blocks it. The exam might ask, 'Which command would you use to allow a stub router to advertise a specific static route?' Answer: eigrp stub leak-map MAP-NAME.
Variance Command: The variance command is a major trap. Candidates forget that the variance value is a multiplier. A variance of 2 does not mean 'only use paths that are twice as good'. It means 'consider paths that are up to twice as bad as the best path'. The question might ask: 'Best path metric is 100. Variance is 3. Which of these metrics will be used?' The correct answer is 250 (because 100 x 3 = 300, and 250 is less than 300). 350 would be excluded.
Named Mode vs Classic Mode: The exam often shows a configuration snippet and asks you to identify whether it is Classic or Named Mode. The giveaway: Classic Mode starts with router eigrp 100 (followed by a number) and uses network statements under the router, followed by interface commands. Named Mode starts with router eigrp NAME and uses address-family keywords. The exam may present a Classic Mode configuration and ask 'What is the problem?' The problem could be that the stub command is not applied inside the address-family.
Equal vs Unequal Load Balancing: The exam tests the distinction. Equal-cost does not require any special configuration (it happens by default if two paths have the same metric). Unequal-cost requires variance. A common question: 'Traffic is not being load balanced over two paths with different metrics. What is missing?' Answer: The variance command.
Metric Calculation for Load Balancing: You will not need to calculate full metrics, but you must know that EIGRP uses bandwidth and delay by default. The k values are tested. A trick question might ask: 'What is the result of setting metric weights 0 1 1 0 0?' This tells EIGRP to use only bandwidth and delay (k1 and k3).
The key definitions to memorise:
- Stub: A router that will not act as a transit router.
- Variance: The multiplier used in unequal-cost load balancing.
- Leak-map: A route-map to selectively leak a route from a stub.
- Address-family: The configuration block in Named Mode.
- Classic Mode: The old style of configuring EIGRP using router eigrp [AS].
A stub router prevents transit traffic and reduces the routing table size at the edge of a network by only advertising a default route back to the hub.
The 'variance' command enables unequal-cost load balancing by acting as a multiplier on the best path's metric to determine which alternate paths are considered valid.
EIGRP Named Mode uses the 'address-family' keyword to group IPv4 and IPv6 configurations, providing a cleaner and more consistent syntax than legacy Classic Mode.
A 'leak-map' allows a stub router to selectively advertise a specific route that would normally be blocked by the stub restriction.
Equal-cost load balancing in EIGRP requires zero configuration; two paths with identical metrics are automatically used.
The default metric weights (K1 and K3) mean EIGRP uses bandwidth and delay to calculate path cost, and changing these weights is rarely seen in production networks.
These come up on the exam all the time. Here's how to tell them apart.
Classic Mode EIGRP
Configuration starts with 'router eigrp [AS-number]'.
Interface-specific commands are configured separately under each interface.
Does not support a unified configuration for both IPv4 and IPv6 in a single block.
Named Mode EIGRP
Configuration starts with 'router eigrp [NAME]'.
All interface and process settings are grouped under an 'address-family' block.
Supports both IPv4 and IPv6 address-families under the same process name.
EIGRP Stub Router
Will not forward transit traffic between two other routers.
Sends a query for a default route rather than a full routing table.
By default, only advertises connected and summary routes to its neighbor.
Normal EIGRP Router
Can forward traffic between any two routers in the topology freely.
Sends and receives the full routing table from its neighbors.
Advertises all learned routes unless filtered by a specific policy.
Equal-Cost Load Balancing
Requires all paths to have the exact same metric value.
Happens automatically without any special command.
Traffic is divided equally across all available paths.
Unequal-Cost Load Balancing
Allows paths with different metric values to be used.
Requires the 'variance' command to be configured.
Traffic is divided proportionally based on the metric of each path.
EIGRP Leak-Map
Used specifically to allow a blocked route from a stub router.
Applies only to the 'eigrp stub' command as a permit filter.
Does not filter routes from the hub; it only unblocks specific routes from the stub.
Standard Route Filter (Distribute-List)
Applies to any router to block incoming or outgoing routes universally.
Uses an access-list or prefix-list to deny certain network prefixes.
Works independently from stub mode, on any router in the topology.
Mistake
A stub router cannot have any outgoing connections or reachable networks.
Correct
A stub router can still have its own connected networks (like end-user devices) and can send traffic out. It simply refuses to forward traffic that comes from one router and goes to another router. It is a 'leaf' in the topology, not a transit point.
Beginners confuse 'stub' with 'isolated'. They think stub means no traffic, when it actually means no 'pass-through' traffic.
Mistake
Unequal-cost load balancing with variance divides traffic exactly equally (50/50) between two links.
Correct
Traffic is divided proportionally based on the metric of each path. A better path (lower metric) receives more traffic than a worse path. EIGRP calculates a 'traffic share count' based on the ratio of the metrics.
People assume 'load balancing' always means an even split, like two lanes of a highway. EIGRP's load balancing is more intelligent, using mathematics to distribute based on link quality.
Mistake
EIGRP Named Mode is a completely new routing protocol that replaces Classic Mode with different behavior.
Correct
Named Mode is solely a configuration syntax change. The underlying EIGRP protocol behavior (hello timers, metrics, DUAL algorithm) remains identical. It is like reorganising your filing cabinet; the actual documents do not change.
Cisco releases 'Named Mode' with a different command structure. Beginners often believe a new syntax means a new protocol, but it is just a better way to write the same instructions.
Mistake
A stub router configured with 'receive-only' cannot send any traffic out at all.
Correct
'Receive-only' in the EIGRP stub context means the router does not advertise any routes to its neighbors. It can still have a default route or static route outbound. It receives routes from others but is silent itself. It can still forward packets based on routes it has learned.
The word 'receive-only' sounds like the router is in 'listen mode' only. It is a common trap in exam questions to imply the router is completely deaf to outgoing traffic.
Mistake
You must use the 'variance' command to achieve any form of load balancing in EIGRP.
Correct
EIGRP performs equal-cost load balancing automatically if two paths have exactly the same metric. The 'variance' command is only needed for unequal-cost load balancing when the metrics are different.
Many beginners think all load balancing needs a special configuration, but basic load balancing (over equal cost links) is automatic in EIGRP, leading to missed exam points.
Reveal each answer, then mark whether you got it right. Score 60%+ to unlock the next chapter.
A stub router is a complete router that speaks EIGRP but will not forward transit traffic. A passive interface stops EIGRP from sending hello packets out of that specific interface altogether, effectively preventing adjacency from being formed on that link. Stub is a global router role; passive is an interface setting.
No. In fact, the `eigrp stub` command can include the `summary` keyword, which instructs the stub router to still send summarised routes. Route summarisation is independent of stub mode, and is often used together for efficient edge routing.
Yes. The default maximum number of paths EIGRP can load balance across is 4. You can increase this up to 32 using the `maximum-paths` command under the address-family. Load balancing will still respect variance if configured.
Named Mode provides consistent syntax across Cisco platforms (IOS, IOS-XE, NX-OS). It allows you to configure both IPv4 and IPv6 under one routing process. It also makes reading a configuration easier because all interface-specific settings are grouped under the address-family instead of being scattered.
The branch router will operate as a normal EIGRP router. It will learn the full routing table from the hub, which can consume memory on a small device. More dangerously, if the branch has two connections back to the hub, it could become a transit point for traffic between those two hub links, causing suboptimal routing.
It means the stub router will not advertise any routes at all to its neighbors. It will only receive routes from the hub. This is useful for a device that only needs to send traffic to the hub and has no local networks to announce.
You've finished Advanced EIGRP Features (Stub, Load Balancing, Named Mode). Continue through the 300-410 study guide to build a complete picture of the exam.
Done with this chapter?