EIGRP for IPv6, also known as EIGRPv3, is a critical topic for the CCNA 200-301 exam (objective 3.5) because it demonstrates how a classic distance-vector routing protocol adapts to the IPv6 world. In real networks, many enterprises still rely on EIGRP for its fast convergence and low overhead, and understanding its IPv6 configuration is essential for dual-stack migration. This lab will walk you through enabling EIGRP for IPv6 on routers, configuring interfaces, and verifying neighbor relationships and routes—skills you'll need both in the exam simulation and on the job.
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Imagine a large office building with multiple floors, each floor managed by a security guard. The guards need to know who is on which floor so they can direct visitors. They use intercoms to share this information. EIGRP for IPv6 is like installing a new intercom system that works specifically with the building's new numbering scheme (IPv6 addresses). Just as the old intercom system used analog signals, EIGRP for IPv4 uses IPv4 addresses. The new digital intercoms (EIGRPv3) use IPv6 addresses and have a different protocol number (88) but the same fundamental operation: guards exchange 'hello' messages every 5 seconds (on most links) to discover each other, and if they don't hear a hello for 15 seconds (hold time), they assume the other guard is out of service. They then exchange full routing information using 'update' messages, which are like sharing a complete list of all floors and who is responsible. The guards also send 'query' messages if they lose a route, asking others if they know a way. The key difference is that the new intercom system (EIGRPv3) requires the guards to be explicitly told to use it on each intercom station (interface), and it uses the router's IPv6 link-local address as the source for all messages, just like each intercom has a unique extension number. The building's main directory (the routing table) now stores IPv6 prefixes instead of IPv4, but the process of updating it remains identical.
EIGRP for IPv6 (often called EIGRPv3) is the IPv6-capable version of the Enhanced Interior Gateway Routing Protocol. It is defined in RFC 7868 and uses the same Diffusing Update Algorithm (DUAL) as its IPv4 counterpart. The key difference is that it runs directly over IPv6, using IPv6 link-local addresses for neighbor communication and IPv6 multicast address FF02::A for hellos. EIGRPv3 is not a separate protocol; it is simply EIGRP adapted for IPv6. On Cisco IOS, EIGRP for IPv6 is configured using the ipv6 router eigrp command, followed by an autonomous system number. Unlike EIGRP for IPv4, EIGRPv3 does not require a network statement; instead, interfaces are enabled individually under the routing process or directly on the interface.
How EIGRP for IPv6 Works Step by Step
Router Configuration: The network engineer enables EIGRP for IPv6 using ipv6 router eigrp ASN in global configuration mode. A router ID is required (IPv4 address format) because the EIGRP process needs a unique identifier. If no router ID is configured, the router will fail to start the process.
Interface Activation: Each interface that should participate in EIGRPv3 must be explicitly enabled using the ipv6 eigrp ASN interface command. This is a major difference from IPv4 where a network statement under the router process could enable EIGRP on multiple interfaces.
Neighbor Discovery: Once enabled, the router sends EIGRP hello packets every 5 seconds (default for most interfaces) to the multicast address FF02::A, sourced from the interface's link-local address. The hello packets include the AS number, hold time (default 15 seconds), and K-values. Neighbors must have the same AS number and matching K-values to form adjacency.
Neighbor Table and Topology Table: When a hello is received, the neighbor is added to the neighbor table. The router then sends an update packet containing all known routes (full topology exchange) to the new neighbor. This update is sent unicast to the neighbor's link-local address. The received routes are stored in the topology table, and DUAL calculates the best path (successor) and feasible successor if available.
Route Advertisement: EIGRPv3 advertises IPv6 prefixes with a metric based on bandwidth and delay (by default). Routes are redistributed into the IPv6 routing table. The show ipv6 route eigrp command displays EIGRP-learned routes.
Key States, Timers, and Defaults
Hello Interval: 5 seconds for most interfaces (60 seconds for NBMA interfaces like Frame Relay).
Hold Time: 15 seconds (three times the hello interval by default).
Multicast Address: FF02::A (all EIGRP routers).
Protocol Number: 88 (same as EIGRP for IPv4).
Metric Weights (K-values): Default K1=1, K2=0, K3=1, K4=0, K5=0 (only bandwidth and delay used).
Router ID: Required, must be a 32-bit number in IPv4 format (e.g., 1.1.1.1). If not configured, EIGRPv3 will not start.
Administrative Distance: 90 for internal routes, 170 for external routes (same as IPv4).
IOS CLI Verification Commands
To verify EIGRP for IPv6 operation, use the following commands:
R1# show ipv6 eigrp neighbors
EIGRP-IPv6 Neighbors for AS(100)
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) Cnt Num
0 Link-local address: GigabitEthernet0/0 13 00:12:34 1 100 0 5
FE80::1R1# show ipv6 eigrp topology
EIGRP-IPv6 Topology Table for AS(100)/ID(1.1.1.1)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
r - reply Status, s - sia Status
P 2001:DB8:1::/48, 1 successors, FD is 28160
via FE80::1, GigabitEthernet0/0
P 2001:DB8:2::/48, 1 successors, FD is 28160
via FE80::2, GigabitEthernet0/1R1# show ipv6 route eigrp
IPv6 Routing Table - default - 5 entries
Codes: C - Connected, L - Local, S - Static, U - Per-user Static route
B - BGP, R - RIP, I1 - ISIS L1, I2 - ISIS L2
IA - ISIS interarea, IS - ISIS summary, D - EIGRP, EX - EIGRP external
ND - ND Default, NDP - ND Prefix, DCE - Destination, NDr - Redirect
O - OSPF Intra, OI - OSPF Inter, OE1 - OSPF ext 1, OE2 - OSPF ext 2
ON1 - OSPF NSSA ext 1, ON2 - OSPF NSSA ext 2
D 2001:DB8:2::/48 [90/28160]
via FE80::2, GigabitEthernet0/1R1# show ipv6 protocols
IPv6 Routing Protocol is "connected"
IPv6 Routing Protocol is "ND"
IPv6 Routing Protocol is "eigrp 100"
EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0
EIGRP maximum hopcount 100
EIGRP maximum metric variance 1
Interfaces:
GigabitEthernet0/0
GigabitEthernet0/1
Redistributing: eigrp 100
Routing for Networks:
GigabitEthernet0/0
GigabitEthernet0/1
Routing Information Sources:
Gateway Distance Last Update
FE80::1 90 00:12:34
FE80::2 90 00:12:35
Distance: (default is 90)Interaction with Related Protocols
EIGRP for IPv6 interacts with other IPv6 routing protocols through redistribution. It can also be used alongside static routes and connected routes. On dual-stack networks, EIGRP for IPv4 and EIGRP for IPv6 run independently, but both use the same autonomous system number (if desired). The DUAL algorithm works identically for both address families. EIGRPv3 does not interact with IPv4 routing; it only populates the IPv6 routing table.
Enable IPv6 Routing Globally
Before configuring EIGRP for IPv6, you must enable IPv6 routing on the router. This is done with the global configuration command `ipv6 unicast-routing`. Without this command, the router will not forward IPv6 packets and EIGRPv3 will not function. This command enables the IPv6 forwarding engine and is required for any IPv6 routing protocol. Verify with `show ipv6 interface brief` to see that interfaces have IPv6 addresses.
Configure EIGRP for IPv6 Process
Enter global configuration mode and create the EIGRP for IPv6 routing process using `ipv6 router eigrp ASN`, where ASN is the autonomous system number (must match on all routers). This command places you in router configuration mode. You must then assign a router ID using `eigrp router-id A.B.C.D`. The router ID is a 32-bit number in IPv4 dotted-decimal format. If not configured, the process will not start. Optionally, you can adjust timers with `timers active-time` or `hello-interval` and `hold-time` under the interface.
Enable EIGRP on Interfaces
EIGRP for IPv6 requires explicit interface activation. For each interface that should participate, enter interface configuration mode and issue `ipv6 eigrp ASN`. This command tells the interface to send and receive EIGRPv3 hello packets and to include its connected subnet in routing updates. Unlike EIGRP for IPv4, there is no `network` command under the router process. You must enable it per interface. Verify with `show ipv6 eigrp interfaces`.
Verify Neighbor Adjacency
After enabling EIGRP on interfaces, check that neighbor adjacencies form. Use `show ipv6 eigrp neighbors` to display neighbors. The output shows the neighbor's link-local address, the interface, hold time, uptime, and sequence numbers. If no neighbors appear, check that both routers have matching AS numbers, K-values, and that the interfaces are up/up. Also ensure that IPv6 link-local addresses are reachable (ping the link-local address).
Verify Routing Table and Topology
Once neighbors are established, verify that routes are being exchanged. Use `show ipv6 route eigrp` to see EIGRP-learned routes in the IPv6 routing table. Use `show ipv6 eigrp topology` to view the topology table, which includes all routes learned from neighbors, their metrics, and the successor/feasible successor status. If routes are missing, check for passive interfaces or mismatched K-values.
Troubleshoot Common Issues
Common problems include: (1) Router ID not configured – use `show ipv6 eigrp` to see if the process is running. (2) AS number mismatch – verify with `show ipv6 eigrp neighbors` and check the AS in the process. (3) K-value mismatch – use `show ipv6 protocols` to compare K-values. (4) Interface not enabled – ensure `ipv6 eigrp ASN` is present on the interface. (5) IPv6 unicast-routing not enabled – check with `show ipv6 interface`. Use debug commands like `debug ipv6 eigrp` for detailed troubleshooting.
In enterprise networks, EIGRP for IPv6 is often deployed in dual-stack environments where both IPv4 and IPv6 routing are needed. For example, a large university with multiple campuses might use EIGRP for both address families to provide fast convergence for internal routing. The network engineer would configure EIGRP for IPv6 on all core routers and distribution switches, using the same AS number for simplicity. One common scenario is migrating from a pure IPv4 EIGRP network to dual-stack. The engineer would first enable IPv6 on all interfaces, then configure EIGRP for IPv6 alongside the existing EIGRP for IPv4. Since both protocols run independently, there is no risk of interference. The engineer must ensure that the router ID is manually set for EIGRPv6, as it is not automatically derived from IPv4 addresses. In production, EIGRP for IPv6 is used for its low overhead and fast convergence. It is particularly useful in networks where OSPFv3 may be too complex or where the team has deep EIGRP expertise. However, one must be careful with the metric calculation: EIGRP for IPv6 uses the same formula as IPv4, but the bandwidth and delay values are taken from the interface configuration. A common misconfiguration is forgetting to set the router ID, which causes the EIGRP process to fail silently. Another issue is mismatched K-values; if one router has non-default K-values, neighbors will not form adjacency. In large networks, the topology table can become large, but EIGRP's DUAL algorithm ensures only feasible successors are kept, limiting memory usage. Network engineers often use route summarization to reduce the size of the topology table and improve convergence. EIGRP for IPv6 supports manual summarization on interfaces with the ipv6 summary-address eigrp command. Overall, EIGRP for IPv6 is a robust choice for IPv6 routing in environments that already use EIGRP.
The CCNA 200-301 exam objective 3.5 covers 'Configure and verify EIGRP for IPv6 (excluding authentication, filtering, manual summarization, redistribution, stub)'. This means you must know how to enable EIGRPv6, configure the router ID, enable it on interfaces, and verify neighbor and route tables. You do NOT need to know advanced features like authentication or redistribution. The exam will test configuration commands and verification outputs. Common wrong answers include: (1) Thinking that EIGRP for IPv6 uses a network statement like IPv4 – it does not; you must enable it per interface. (2) Forgetting that a router ID is required – many candidates assume it is optional or derived from an IPv6 address. (3) Confusing the multicast address FF02::A with FF02::5 (OSPFv3) or FF02::9 (RIPng). (4) Assuming that EIGRP for IPv6 uses the same process as IPv4 – they are separate; you must configure both if you want both. Specific values to memorize: Hello interval 5 seconds (default), hold time 15 seconds, multicast address FF02::A, protocol number 88, administrative distance 90. Command outputs to recognize: show ipv6 eigrp neighbors shows link-local addresses; show ipv6 route eigrp shows routes with code 'D'. Calculation traps: Metric calculation is not tested for IPv6 specifically, but you should know that bandwidth and delay are used. Decision rule for scenario questions: If the question asks about enabling EIGRP for IPv6, always look for the router ID configuration and per-interface enablement. If a neighbor is not forming, check for AS mismatch, K-value mismatch, or missing router ID. Eliminate any answer that suggests a network statement or that EIGRP for IPv6 uses IPv4 addresses for neighbor communication (it uses link-local).
EIGRP for IPv6 requires 'ipv6 unicast-routing' to be enabled globally.
The EIGRP for IPv6 process is created with 'ipv6 router eigrp ASN' and requires a manually configured router ID using 'eigrp router-id A.B.C.D'.
Interfaces are enabled with 'ipv6 eigrp ASN' under interface configuration mode; no network statement is used.
EIGRP for IPv6 uses multicast address FF02::A for hellos and link-local addresses for neighbor communication.
Default hello interval is 5 seconds, hold time is 15 seconds (most interfaces).
Administrative distance is 90 for internal routes, 170 for external routes.
Key verification commands: 'show ipv6 eigrp neighbors', 'show ipv6 eigrp topology', 'show ipv6 route eigrp', 'show ipv6 protocols'.
These come up on the exam all the time. Here's how to tell them apart.
EIGRP for IPv4
Uses network statements under router eigrp to enable interfaces.
Router ID is automatically derived from the highest IPv4 address on a loopback or physical interface.
Neighbor communication uses IPv4 unicast or multicast 224.0.0.10.
Hello packets sourced from interface IPv4 address.
Routes are IPv4 prefixes.
EIGRP for IPv6
No network statement; interfaces enabled with 'ipv6 eigrp ASN' under interface config.
Router ID must be manually configured with 'eigrp router-id' (IPv4 format).
Neighbor communication uses IPv6 multicast FF02::A and link-local addresses.
Hello packets sourced from interface link-local IPv6 address.
Routes are IPv6 prefixes.
Mistake
EIGRP for IPv6 uses a network statement under the router process to enable interfaces.
Correct
EIGRP for IPv6 does not use network statements. Each interface must be explicitly enabled with the 'ipv6 eigrp ASN' command.
This belief persists because EIGRP for IPv4 uses network statements, so candidates assume IPv6 works the same way.
Mistake
EIGRP for IPv6 automatically uses the router's IPv6 address as the router ID.
Correct
EIGRP for IPv6 requires a manually configured router ID in IPv4 format (e.g., 1.1.1.1). It does not derive from any IPv6 address.
Candidates may think the router ID can be an IPv6 address since the protocol is for IPv6, but EIGRP's router ID is always a 32-bit number.
Mistake
EIGRP for IPv6 and EIGRP for IPv4 can share the same process and configuration.
Correct
They are separate processes. You must configure 'ipv6 router eigrp' for IPv6 and 'router eigrp' for IPv4 independently.
Because both use the same AS number, candidates assume one process handles both, but Cisco IOS treats them as different address families.
Mistake
EIGRP for IPv6 uses the multicast address FF02::5 for hellos.
Correct
EIGRP for IPv6 uses FF02::A (all EIGRP routers). FF02::5 is used by OSPFv3.
Candidates often confuse multicast addresses for different routing protocols, especially OSPF and EIGRP.
Reveal each answer, then mark whether you got it right. Score 60%+ to unlock the next chapter.
Yes, absolutely. EIGRP for IPv6 requires a manually configured router ID in IPv4 dotted-decimal format (e.g., 1.1.1.1). Without it, the EIGRP process will not start. This is a common pitfall on the CCNA exam. Use the 'eigrp router-id' command under the 'ipv6 router eigrp' configuration mode. The router ID must be unique within the EIGRP domain.
Yes, you can use the same autonomous system number for both address families. They are separate processes but can share the same AS number. However, they are configured independently: 'router eigrp ASN' for IPv4 and 'ipv6 router eigrp ASN' for IPv6. The AS number must match between neighbors for each respective address family.
Several reasons: (1) Router ID not configured. (2) AS number mismatch. (3) K-values mismatch (use default K1=1, K2=0, K3=1, K4=0, K5=0). (4) Interface not enabled with 'ipv6 eigrp ASN'. (5) IPv6 unicast-routing not enabled globally. (6) Access list blocking EIGRP packets (protocol 88). Use 'debug ipv6 eigrp' to see hello packets and errors.
Yes, the metric formula is identical: metric = (K1 * bandwidth + (K2 * bandwidth)/(256 - load) + K3 * delay) * 256, with default K values using only bandwidth and delay. The bandwidth and delay values are taken from the interface configuration. The metric is computed the same way for IPv6 routes.
Use 'show ipv6 eigrp' to see the process and router ID. Use 'show ipv6 eigrp interfaces' to see which interfaces are enabled. Use 'show ipv6 eigrp neighbors' to see neighbor adjacencies. Use 'show ipv6 route eigrp' to see learned routes. Also, 'show ipv6 protocols' lists all IPv6 routing protocols, including EIGRP.
'ipv6 router eigrp ASN' enters the EIGRP configuration mode for IPv6. 'router eigrp ASN' enters the EIGRP configuration mode for IPv4. They are separate configuration contexts. You must use the appropriate command for the address family you want to configure.
No, not directly. EIGRP for IPv4 and EIGRP for IPv6 are separate protocols that operate on different address families. Redistribution between them would require a translation between IPv4 and IPv6 routes, which is not supported natively. You can redistribute between EIGRP for IPv6 and other IPv6 routing protocols (e.g., OSPFv3) using the 'redistribute' command under the IPv6 router process.
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