Discovering EIGRP: The Ultimate Guide to Cisco's Advanced Routing Protocol
Ever feel lost in the world of network routing protocols? If you're looking for an advanced option beyond the basics, Cisco's Enhanced Interior Gateway Routing Protocol (EIGRP) might be your answer.
One such robust and efficient solution developed by Cisco Systems is the Enhanced Interior Gateway Routing Protocol, or EIGRP, which is used in the complex landscape of network routing. EIGRP does things a bit differently than your traditional routing protocols, taking things to a whole next level, while at the same time integrating the very best features of both distance vector and link state routing protocols, offering the best of both worlds when it comes to speed, scalability, and flexibility. Whether a small enterprise network or a large corporate network, EIGRP provides a dynamic and reliable foundation to uniformly support the flow of data with the least amount of downtime.
Here, we discuss this part very carefully because of EIGRP, the complex protocols touching algorithms, PhD-degree-worthy computations, flexible configurations, and why it is so advantageous strategically in a modern network environment that is normally buried out the depths of the routing parameters. Follow along with us as we delve into how EIGRP allows this paradigm shift to come to pass in your network operations.
What is EIGRP?
Enhanced Interior Gateway Routing Protocol (EIGRP) is a dynamic routing protocol developed by Cisco. EIGRP is designed to automate routing decisions and configuration in large and complex networks, providing efficient and reliable routing with rapid convergence times.
Is EIGRP used anymore?
Yes, EIGRP is still in use, especially in environments where Cisco equipment is prevalent. It continues to be favored for its efficiency and rapid convergence, making it suitable for large-scale networks.
Why is EIGRP used?
EIGRP is used because it combines the benefits of both distance-vector and link-state protocols, offering fast convergence, scalability, and efficient bandwidth usage. It supports multiple network layer protocols and provides features like load balancing and route summarization.
Is EIGRP only for Cisco?
No. Originally, EIGRP was a proprietary protocol exclusive to Cisco. However, Cisco has made EIGRP an open standard, allowing it to be implemented on non-Cisco devices as well.
Is EIGRP removed from CCNA?
Yes, EIGRP has been removed from the CCNA (Cisco Certified Network Associate) certification curriculum. Cisco decided to shift the focus towards more foundational networking concepts and other widely used protocols, such as OSPF.
What are the Basic Features of EIGRP?
The Enhanced Interior Gateway Routing Protocol (EIGRP) is a routing protocol developed by Cisco that combines elements of both distance-vector and link-state routing protocols. It is considered a Hybrid protocol due to its unique characteristics. EIGRP operates at the network layer and is identified by protocol number 88 in the networking stack.
Some of the features of EIGRP are listed and simply explained below.
- Rapid Convergence: EIGRP uses the Diffusing Update Algorithm (DUAL) to provide rapid convergence and ensure loop-free routing. This allows the network to quickly adapt to changes such as link failures.
- Efficient Use of Bandwidth: EIGRP uses partial and bounded updates instead of periodic updates. This means that updates are only sent when there is a change in the network topology, and only the affected part of the routing table is updated, reducing the use of bandwidth.
- Support for Multiple Network Protocols: EIGRP is capable of routing for IP, IPX, and AppleTalk through protocol-dependent modules, making it versatile for different network environments.
- Scalability: EIGRP is suitable for large-scale networks due to its efficient routing algorithm and low bandwidth usage. It can handle large and complex network topologies with ease.
- Composite Metric: EIGRP uses a composite metric based on bandwidth, delay, load, and reliability to calculate the best path to each destination. This provides a more accurate and reliable route selection compared to simpler metrics like hop count.
- Load Balancing: EIGRP supports load balancing across equal and unequal cost paths, allowing for more efficient use of network resources and better traffic distribution.
- Route Summarization: EIGRP supports both manual and automatic route summarization, which helps reduce the size of routing tables and improves the efficiency of the routing process.
- Security: EIGRP includes support for authentication, ensuring that routing information comes from trusted sources, which enhances the security of the routing process.
What Type of Protocol is the Enhanced Interior Gateway Routing Protocol?
The Enhanced Interior Gateway Routing Protocol (EIGRP) is a hybrid routing protocol that combines features of both distance-vector and link-state protocols. It is often referred to as an advanced distance-vector protocol. EIGRP uses distance-vector mechanisms for route advertisement and the DUAL algorithm to provide rapid convergence and loop-free routing. This hybrid nature allows EIGRP to provide the best of both worlds, offering efficient routing, quick convergence, and scalability for large and complex networks.
How does EIGRP work?
The Enhanced Interior Gateway Routing Protocol (EIGRP) functions through the establishment of neighbor relationships and the exchange of routing information with these neighboring routers. Below is an in-depth explanation of how this process operates.
1. Neighbor Discovery and Maintenance
EIGRP routers discover and maintain information about their directly connected neighbors using Hello packets. These packets are sent periodically to identify and maintain neighbor relationships. When a router receives a Hello packet, it adds the sender to its neighbor table.
2. Reliable Transport Protocol (RTP)
EIGRP uses RTP to ensure the reliable delivery of routing updates. RTP supports both reliable and unreliable delivery of packets, depending on the type of packet being sent. For example, Hello packets are sent unreliably, while updates, queries, and replies are sent reliably.
3. Diffusing Update Algorithm (DUAL)
DUAL is the key algorithm that EIGRP uses to calculate the shortest path to a destination. It guarantees loop-free and efficient routing. DUAL maintains the following tables:
- Neighbor Table: Stores information about all the neighbors.
- Topology Table: Contains all the routes advertised by neighbors, including feasible successors (backup routes).
- Routing Table: Holds the best route to each destination as determined by the metric calculations.
4. Route Calculation
EIGRP uses a composite metric based on bandwidth, delay, load, and reliability to calculate the best path to a destination. The default metric calculation involves bandwidth and delay. The best route to a destination is called the successor, and any backup routes are called feasible successors.
5. Partial and Bounded Updates
Unlike protocols that send periodic updates, EIGRP sends partial and bounded updates. This means updates are sent only when there is a change in the network topology, and only the affected routes are updated. This minimizes bandwidth usage and improves efficiency.
6. Route Summarization and Scalability
EIGRP supports both automatic and manual route summarization. This feature helps reduce the size of routing tables and limits the scope of routing updates, making EIGRP scalable for large networks.
7. Load Balancing
EIGRP supports load balancing over equal and unequal cost paths. This allows EIGRP to distribute traffic more evenly across multiple links, enhancing network performance and resource utilization.
8. Authentication
EIGRP supports route authentication, ensuring that routing information is exchanged only with trusted routers. This enhances the security of the routing protocol.
What are the essential EIGRP concepts that should be learned?
Understanding some of the below-given concepts is crucial for configuring and troubleshooting EIGRP in a network environment, ensuring efficient and reliable routing operations.
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EIGRP Tables: EIGRP maintains three different tables in order to carry out its operations effectively, namely the Neighbor Table, the Topology Table, and the IP Routing Table.
- Neighbor Table: The Neighbor Table in EIGRP is where a router stores information about its directly connected routers, also known as neighbors. This table includes details like the neighbor's IP address and the interface through which they are reachable. The primary purpose is to keep track of the routers with which EIGRP has established adjacencies.
- Topology Table: The Topology Table stores all the routing information received from EIGRP neighbors. This includes all possible routes to each destination, not just the best routes. Each entry in the topology table contains the destination network, the metrics for the routes, and the successor and feasible successor routes. This table is crucial for EIGRP's decision-making process regarding route selection and backup paths??.
- Routing Table: The Routing Table contains the best routes to each destination as determined by EIGRP. These are the routes used to forward packets. The best route is known as the "successor", and it is the one with the lowest cost (metric) to the destination. The routing table is derived from the topology table, but only the most efficient routes are included??.
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Feasible Successors: Feasible Successors are backup routes to a destination. These routes are stored in the topology table and can be used immediately if the primary route (successor) fails. A route is considered a feasible successor if its reported distance (RD) is less than the feasible distance (FD) of the current successor. This ensures a loop-free topology??.
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Route States: EIGRP routes can be in various states:
- Active: A route is active if the primary route to a destination fails and no feasible successors are available. The router actively queries its neighbors for alternative paths.
- Passive: A route is passive when it is in a stable state, meaning the router has a successor and potentially feasible successors for that route. Most routes in a stable network are in the passive state??.
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Packet Formats: EIGRP uses several types of packets for its operations:
- Hello Packets: Used to discover and maintain neighbor relationships. EIGRP routers send hello packets to multicast address 224.0.0.10. If hello packets are not received from a neighbor within a certain time (hold time), the neighbor is considered down.
- Update Packets: Convey routing information. Sent only when a route is first established or when there is a change in the topology. Update packets contain route entries and are sent as unicasts to specific neighbors or as multicasts if there are multiple neighbors to notify.
- Query Packets: Sent when a route goes active to find an alternative path. Used when a router loses a route and seeks alternative paths from its neighbors. Query packets are multicast to all neighbors to request this information.
- Reply Packets: Responses to query packets. These packets provide the requested routing information. If a queried route is known, the reply packet contains the route information; if not, it indicates the route is unknown.
- Acknowledgment Packets: Acknowledge receipt of update, query, and reply packets??. ACK packets ensure reliable delivery of the other EIGRP packets. They are always unicast and are very small, containing only the necessary acknowledgment information.
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Route Tagging: Route Tagging in EIGRP involves attaching a tag to a route to control routing decisions and policies. Tags can be used for route filtering, policy-based routing, and preventing routing loops in complex topologies.
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EIGRP K Values: EIGRP uses K values to determine the composite metric for routes. These K values are configurable and represent different routing metrics:
- K1: Bandwidth
- K2: Load
- K3: Delay
- K4: Reliability
- K5: MTU (not commonly used)
The default K values focus on bandwidth and delay (K1 and K3), ensuring that these metrics primarily influence route selection??.
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EIGRP Diffusing Update Algorithm (DUAL): DUAL is the algorithm EIGRP uses to guarantee loop-free and efficient route computation. It maintains the topology table and uses it to calculate the shortest path and backup paths. DUAL allows for rapid convergence by switching to a feasible successor immediately if the primary route fails, minimizing downtime and packet loss. The algorithm ensures that all routers in the network have a consistent view of the topology, allowing for efficient and reliable routing decisions??.
How to Configure EIGRP on Cisco Routers?
The following configuration enables EIGRP on the router, specifies the networks to be included in EIGRP, and sets optional configurations such as metrics, passive interfaces, authentication, route redistribution, and summarization. The network commands specify which interfaces EIGRP will operate on by identifying the network addresses associated with those interfaces.
Router(config)# router eigrp 100
Router(config-router)# network 192.168.1.0 0.0.0.255
Router(config-router)# network 10.1.1.0 0.0.0.255
Router(config-router)# metric weights 0 1 0 1 0 0
Router(config-router)# passive-interface default
Router(config-router)# no passive-interface GigabitEthernet0/0
Router(config-router)# redistribute static
Router(config-router)# redistribute ospf 1
Router(config-router)# auto-summary
Router(config-if)# ip authentication mode eigrp 100 md5
Router(config-if)# ip authentication key-chain eigrp 100 MY_KEY_CHAIN
You may configure EIGRP by following the next steps:
- To enable EIGRP on the router, run the next command:
Router(config)# router eigrp 100 - To specify the network, run the next command:
Router(config-router)# network 192.168.1.0 0.0.0.255
Router(config-router)# network 10.1.1.0 0.0.0.255 - To configure EIGRP metrics, run the next command: (Optional)
Router(config-router)# metric weights 0 1 0 1 0 0 - To configure passive interfaces, run the next command: (Optional)
Router(config-router)# passive-interface default
Router(config-router)# no passive-interface GigabitEthernet0/0 - To set EIGRP authentication, run the next command: (Optional)
Router(config-if)# ip authentication mode eigrp 100 md5
Router(config-if)# ip authentication key-chain eigrp 100 MY_KEY_CHAIN - To redistribute routes, run the next command: (Optional)
Router(config-router)# redistribute static
Router(config-router)# redistribute ospf 1 - To enable route summarization, run the next command: (Optional)
Router(config-router)# auto-summary
What are the Advantages and Disadvantages of EIGRP?
The Enhanced Interior Gateway Routing Protocol (EIGRP), made by Cisco, is liked for its strength and adaptability This routing protocol is useful in several network environments ranging from small businesses to large complicated networks. Despite EIGRP's many advantages, it has some negatives. These problems can affect how suitable it is in certain situations that need multivendor interoperability and specific routing needs. We will consider both the positives and negatives of EIGRP show its place in today's networking world.
Advantages of EIGRP
Below are some of the advantages that contribute to making EIGRP a resilient and adaptable routing protocol that is well-suited for a diverse array of network environments, spanning from modest-sized businesses to expansive, intricate networks.
- Quick Convergence: EIGRP deploys the Diffusing Update Algorithm or DUAL, allowing it to modify swiftly post a topology alteration. This feature minimizes downtime and assures network stability.
- Bandwidth Efficiency: EIGRP transmits partial and bounded updates strictly when there's a network topology modification. This method lowers bandwidth overuse, unlike protocols that transmit regular full updates.
- Scalability: EIGRP boasts impressive scalability, adept at managing large and intricate network configurations. It suits both minor and major enterprise networks.
- Load Balancing: EIGRP allows both equal and unequal cost load balancing, enabling use of multiple paths to a target point, providing redundant routing and optimizing network resource usage.
- Composite Metric: EIGRP utilizes composite metrics derived from bandwidth, delay, load, and reliability. This offers a reliable and adjustable way of choosing the optimal path to a target compared to simpler metrics like hop count.
- Route Summarization: EIGRP supports both auto and manual route summarization aiding in shrinking routing table sizes along with reduction in overall routing information that necessitates processing and exchange.
- Protocol Independence: EIGRP can create routes for multiple network layer protocols such as IP, IPX, AppleTalk through protocoldependent modules.
- Authentication: EIGRP includes support for authentication, ensuring that routing updates are exchanged only between trusted routers, which enhances network security.
Disadvantages of EIGRP
Below are some disadvantages that highlight the limitations and challenges of using EIGRP, which can affect its suitability for certain network environments, particularly in scenarios involving multi-vendor interoperability and specific routing requirements.
- Ownership: Cisco first developed EIGRP as a private protocol. It was later made accessible to all, but many corporations link it primarily with Cisco gear. This may curb its use in multisupplier settings.
- Intricacy: EIGRP has more detail and is harder to set up and solve problems with than simpler routing protocols like RIP. To effectively manage a network with EIGRP, network managers need substantial knowledge of its functions and workings.
- Excessive Resource Utilization: EIGRP can use more CPU and memory resources, especially in large networks with many routes and frequent topology modifications. For older or less powerful hardware, this might be a factor.
- Restricted Universal Support: Even as an open standard, EIGRP doesn't enjoy the same broad support as other protocols like OSPF. In diverse network settings, this can cause compatibility issues.
What is the Difference Between BGP and EIGRP?
In network routing protocols, the Border Gateway Protocol (BGP) and Enhanced Interior Gateway Routing Protocol (EIGRP) play distinct roles. They meet different networking needs. Both these protocols are key to ensuring smooth data flow across networks but they vary greatly in their design, use, and functions.
| Feature | BGP (Border Gateway Protocol) | EIGRP (Enhanced Interior Gateway Routing Protocol) |
|---|---|---|
| Type | Exterior | Interior |
| Operation | TCP, Path Vector | DUAL (Diffusing Update Algorithm) |
| Focus | Policies, Path Attributes, Routing Rules | Metrics (Bandwidth, Delay, Load, Reliability) |
| Usage | Internet Routing, Inter-AS Communication | Internal Routing within an Organization |
| Scalability | Highly Scalable (Large, Complex Networks) | Scalable within Large Enterprises (Single AS) |
| Convergence | Slower (Large Networks) | Faster (DUAL Algorithm) |
Table 1. BGP vs EIGRP
While BGP is an inter-domain (or exterior) routing protocol, meaning it is used to exchange routing information between different autonomous systems (ASes) on the internet, EIGRP is an intra-domain (or interior) routing protocol, meaning it is used within a single autonomous system.
EIGRP uses the Diffusing Update Algorithm (DUAL) and combines features of distance-vector and link-state protocols. It relies on metrics like bandwidth, delay, load, and reliability for route calculation. However, BGP operates over TCP and uses a path vector mechanism. It focuses on policies, path attributes, and rules for routing decisions.
In contrast to EIGRP which is used within organizations for internal routing, BGP is used mainly by ISPs and large organizations for internet routing and inter-AS communication.
Furthermore, BGP is highly scalable and suitable for large and complex networks with numerous ASes. But, EIGRP is scalable within large enterprises but typically confined to a single AS.
Lastly, BGP has slower convergence compared to interior routing protocols because it deals with large and complex networks. On the other hand, EIGRP provides fast convergence due to the DUAL algorithm, making it suitable for dynamic and large internal networks.
What is the Difference Between OSPF and EIGRP?
Different network routing protocols like Open Shortest Path First (OSPF) and Enhanced Interior Gateway Routing Protocol (EIGRP) offer unique features. OSPF is an open standard protocol praised for its scalability and widespread support in multivendor environments. OSPF is often chosen for large-scale, intricate networks. EIGRP, a Ciscodeveloped proprietary protocol, is famous for its fast convergence and adaptability in Cisco-based networks. Both types of routing protocols play essential roles in finding the best routes for data transfer but differ in their foundational algorithms, configuration challenges, and functional surroundings.
| Feature | OSPF (Open Shortest Path First) | EIGRP (Enhanced Interior Gateway Routing Protocol) |
|---|---|---|
| Type | Link-State | Hybrid (Distance-Vector & Link-State) |
| Operation | Dijkstra's Algorithm, Hierarchical (Areas) | DUAL Algorithm, Separate Tables |
| Usage | Wide range of networks, Scalability & Robustness | Primarily Cisco environments, Multi-protocol |
| Convergence | Fast (Flooding LSAs) | Very Fast (DUAL) |
| Metric | Cost (Bandwidth) | Composite (Bandwidth, Delay, Load, Reliability) |
Table 2. OSPF vs EIGRP
While OSPF is a link-state routing protocol used within a single autonomous system, EIGRP is a hybrid routing protocol combining distance-vector and link-state features.
OSPF maintains a complete map of the network topology, which it uses to calculate the shortest path using Dijkstra's algorithm. It operates within a hierarchical structure with areas. On the other hand, EIGRP uses DUAL for route calculation and maintains separate tables for neighbors, topology, and routing information. It relies on composite metrics including bandwidth, delay, load, and reliability.
OSPF is widely used in various types of networks, known for its scalability and robustness. But, EIGRP is predominantly used in Cisco environments and supports multiple network protocols.
In contrast to OSPF which has fast convergence due to its efficient flooding of link-state advertisements (LSAs) and quick recalculation of routes, EIGRP offers very fast convergence due to the DUAL algorithm.
Lastly, OSPF uses a cost metric based on the bandwidth of the links. However, EIGRP uses a composite metric, which allows for more granular and flexible route selection.
Why is EIGRP better than RIP?
Yes. In the networking world, Enhanced Interior Gateway Routing Protocol (EIGRP) and Routing Information Protocol (RIP) guide data traffic across networks effectively. EIGRP is a more preferred option than RIP because of its advanced attributes. Despite being one of the oldest distance vector routing protocols known for its simplicity and easy configuration, RIP has slower convergence times, limited scalability, and a hop count limit. Cisco developed EIGRP to overcome these restrictions with quick convergence, more scalability, and better routing metrics. This makes it an efficient solution for current network environments. Recognizing these differences underscores why EIGRP is often chosen over RIP in both enterprise-grade and intricate networking setups.
While EIGRP uses the DUAL algorithm for rapid convergence, ensuring quick adaptation to network changes, RIP has slower convergence because it relies on periodic updates and a simple distance-vector algorithm.
EIGRP can handle larger and more complex networks efficiently. However, RIP has limited scalability with a maximum hop count of 15, making it unsuitable for larger networks.
In contrast to EIGRP which uses a composite metric based on multiple factors (bandwidth, delay, load, reliability), providing more accurate and reliable routing decisions, RIP uses hop count as the sole metric, which can lead to suboptimal routing decisions.
EIGRP sends partial and bounded updates, reducing unnecessary bandwidth usage. But, RIP sends full routing table updates at regular intervals, leading to higher bandwidth usage.
While EIGRP supports unequal cost load balancing, allowing for better utilization of available paths, RIP only supports equal cost load balancing, limiting its flexibility.
How to Interpret EIGRP Command Outputs?
To effectively manage and troubleshoot EIGRP, it's crucial to understand the command outputs. We'll look at some key EIGRP commands, their typical outputs, and how to interpret them. Understanding these outputs helps in monitoring the EIGRP network, diagnosing issues, and ensuring optimal routing performance.
1. show ip eigrp neighbors
This command displays the EIGRP neighbors and their status.
Example Output:
Router# show ip eigrp neighbors
EIGRP-IPv4 Neighbors for AS(100)
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) Cnt Num
0 10.1.1.2 Gi0/0 13 01:23:45 1 5000 0 12
1 192.168.1.2 Gi0/1 12 02:01:30 2 5000 0 20
Key Fields:
- H: Index number of the neighbor.
- Address: IP address of the neighbor.
- Interface: Interface through which the neighbor is reachable.
- Hold: Time in seconds before declaring the neighbor down if no Hello packets are received.
- Uptime: Duration since the neighbor relationship was established.
- SRTT (Smooth Round-Trip Time): Average time for a packet to travel to the neighbor and back.
- RTO (Retransmission Timeout): Time interval for retransmitting packets.
- Q Cnt: Number of queued EIGRP packets.
- Seq Num: Sequence number of the last update packet received from the neighbor.
2. show ip eigrp topology
This command shows the EIGRP topology table, which contains all the routes EIGRP knows about, including successors and feasible successors.
Example Output:
Router# show ip eigrp topology
EIGRP-IPv4 Topology Table for AS(100)/ID(10.1.1.1)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply, r - reply Status, s - sia Status
P 10.1.1.0/24, 1 successors, FD is 2816 via 10.1.1.2 (2816/2160), GigabitEthernet0/0
P 192.168.1.0/24, 1 successors, FD is 2172416 via 192.168.1.2 (2172416/2816), GigabitEthernet0/1
Key Fields:
- Codes: Status of the route (P - Passive, A - Active).
- Network: Network prefix.
- Successors: Number of successors for the route.
- FD (Feasible Distance): The lowest calculated metric to reach the destination.
- via: The next-hop address and interface used to reach the destination.
- (X/Y): Reported Distance (RD) and Feasible Distance (FD). RD is the metric reported by the neighbor, and FD is the best metric to the destination.
3. show ip route eigrp
This command displays the routes installed in the routing table that were learned via EIGRP.
Example Output:
Router# show ip route eigrp
D 10.1.1.0/24 [90/2816] via 10.1.1.2, 00:23:45, GigabitEthernet0/0
D 192.168.1.0/24 [90/2172416] via 192.168.1.2, 01:23:30, GigabitEthernet0/1
Key Fields:
- D: Indicates the route was learned via EIGRP.
- Network: The destination network.
- [90/2816]: Administrative distance (90) and the metric (2816).
- via: The next-hop IP address.
- Uptime: Duration since the route was installed in the routing table.
- Interface: Interface used to reach the next hop.
4. show ip protocols
This command provides details about the EIGRP configuration and status.
Example Output:
Router# show ip protocols
Routing Protocol is "eigrp 100"
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Default networks flagged in outgoing updates
Default metric is 0, retransmit interval is 0 seconds
EIGRP-IPv4 Neighbors:
10.1.1.2
192.168.1.2
Maximum path: 4
Routing for Networks:
10.1.1.0
192.168.1.0
Routing Information Sources:
Gateway Distance Last Update
10.1.1.2 90 00:23:45
192.168.1.2 90 01:23:30
Key Fields:
- Routing Protocol: Indicates EIGRP and the autonomous system number.
- Neighbors: Lists EIGRP neighbors.
- Maximum path: Number of paths EIGRP can load balance.
- Routing for Networks: Networks being advertised by EIGRP.
- Routing Information Sources: Gateways providing routing information, their distance, and the last update time.