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EIGRPInterface Config

ip hello-interval eigrp [as] [secs]

Configures the EIGRP hello interval on an interface, overriding the default hello interval for the specified autonomous system.

Definition: ip hello-interval eigrp [as] [secs] is a Cisco IOS interface config command. Configures the EIGRP hello interval on an interface, overriding the default hello interval for the specified autonomous system.

Overview

The `ip hello-interval eigrp` command is used to modify the EIGRP hello interval on a specific interface for a given autonomous system (AS). By default, EIGRP sends hello packets every 5 seconds on high-bandwidth links (including LAN interfaces) and every 60 seconds on low-bandwidth multipoint links (such as Frame Relay or ATM). The hello interval determines how often a router advertises its presence to neighbors; it is also used to detect neighbor failures (via the hold time, which is typically three times the hello interval).

Adjusting the hello interval can be necessary in scenarios where faster convergence is desired (by reducing the interval) or where network congestion or slow links require a longer interval to avoid excessive control traffic. This command is an interface-level configuration that overrides the global or per-interface default for the specified AS. It is typically used in conjunction with the `ip hold-time eigrp` command to maintain the hold time ratio (default 3:1).

Network engineers reach for this command when they need to tune EIGRP convergence behavior on specific links, such as in a DMVPN environment where spoke routers may need faster failure detection, or on serial links where reducing hello overhead is beneficial. The command is applied in interface configuration mode and takes effect immediately; the running configuration is updated, and the new interval is used for subsequent hello transmissions. It is important to note that changing the hello interval does not automatically adjust the hold time; the hold time must be changed separately if a different ratio is desired.

The command is available in all IOS versions that support EIGRP, and its behavior is consistent across 12.x, 15.x, and 16.x trains. Understanding this command is essential for CCNA and CCNP candidates as it appears in both configuration and troubleshooting scenarios, particularly in the context of EIGRP neighbor formation and stability.

Syntax·Interface Config
ip hello-interval eigrp [as] [secs]

When to Use This Command

  • On slow WAN links (e.g., Frame Relay) to increase hello interval and reduce overhead
  • To speed up convergence on high-speed LAN segments by decreasing hello interval
  • When tuning EIGRP timers to match neighbor requirements for adjacency formation
  • In hub-and-spoke topologies to adjust hello intervals on spoke interfaces for better scalability

Parameters

ParameterSyntaxDescription
as<1-65535>The EIGRP autonomous system number. This must match the AS number configured under the EIGRP routing process. Common mistake: using a different AS number than the one configured globally, which will cause the command to have no effect.
secs<1-65535>The hello interval in seconds. Valid values are from 1 to 65535. The default is 5 seconds for most interfaces and 60 seconds for low-bandwidth multipoint interfaces. Setting this too low (e.g., 1 second) can increase CPU load and bandwidth usage; setting it too high (e.g., 180 seconds) may delay neighbor failure detection.

Command Examples

Set hello interval to 10 seconds on GigabitEthernet0/1 for AS 100

ip hello-interval eigrp 100 10
R1(config-if)# ip hello-interval eigrp 100 10
R1(config-if)# end
R1# show ip eigrp 100 interfaces GigabitEthernet0/1
EIGRP-IPv4 Interfaces for AS(100)
                    Xmit Queue   Mean   Pacing Time   Multicast    Pending
Interface        Peers  Un/Reliable  SRTT   Un/Reliable   Flow Timer   Routes
Gi0/1              1        0/0       1       0/10         50           0
  Hello interval: 10 secs, Hold time: 30 secs

The command sets hello interval to 10 seconds. The 'show ip eigrp interfaces' output confirms the new hello interval (10 secs) and the automatically adjusted hold time (30 secs, which is 3x hello interval).

Set hello interval to 60 seconds on Serial0/0/0 for AS 200

ip hello-interval eigrp 200 60
R2(config-if)# ip hello-interval eigrp 200 60
R2(config-if)# do show ip eigrp 200 interfaces Serial0/0/0
EIGRP-IPv4 Interfaces for AS(200)
                    Xmit Queue   Mean   Pacing Time   Multicast    Pending
Interface        Peers  Un/Reliable  SRTT   Un/Reliable   Flow Timer   Routes
Se0/0/0            1        0/0       1       0/60         50           0
  Hello interval: 60 secs, Hold time: 180 secs

The hello interval is set to 60 seconds. The output shows the new hello interval and the hold time (180 secs) automatically set to 3 times the hello interval. This is typical for slow links to reduce hello traffic.

Understanding the Output

The 'show ip eigrp interfaces' command displays EIGRP interface parameters. The 'Hello interval' field shows the configured hello interval in seconds. The 'Hold time' is automatically set to 3 times the hello interval by default (unless manually changed with 'ip hold-time eigrp').

A shorter hello interval (e.g., 5 seconds) provides faster convergence but increases overhead; a longer interval (e.g., 60 seconds) reduces overhead but slows down neighbor loss detection. The hold time must be greater than the hello interval; if mismatched, neighbors may not form adjacency. In the output, also check the 'Peers' column to ensure adjacency is established.

Configuration Scenarios

Adjusting EIGRP Hello Interval on a Fast Ethernet Link for Faster Convergence

A network engineer wants to reduce the EIGRP hello interval on a high-speed link between two core routers to achieve faster neighbor failure detection and convergence. The default 5-second interval is too slow for the required sub-second convergence.

Topology

R1(Gi0/0)---10.0.12.0/30---(Gi0/0)R2

Steps

  1. 1.Step 1: Enter global configuration mode: R1# configure terminal
  2. 2.Step 2: Enter interface configuration mode for GigabitEthernet0/0: R1(config)# interface GigabitEthernet0/0
  3. 3.Step 3: Set the EIGRP hello interval to 1 second for AS 100: R1(config-if)# ip hello-interval eigrp 100 1
  4. 4.Step 4: (Optional) Adjust the hold time to maintain the default 3:1 ratio: R1(config-if)# ip hold-time eigrp 100 3
  5. 5.Step 5: Exit configuration mode: R1(config-if)# end
Configuration
!
interface GigabitEthernet0/0
 ip address 10.0.12.1 255.255.255.252
 ip hello-interval eigrp 100 1
 ip hold-time eigrp 100 3
!

Verify: Use 'show ip eigrp 100 interfaces GigabitEthernet0/0 detail' and look for 'Hello interval' field. Expected output: 'Hello interval is 1 sec'.

Watch out: If the hold time is not adjusted, it remains at the default (15 seconds), which may cause premature neighbor loss if hellos are delayed. Always adjust hold time proportionally.

Increasing EIGRP Hello Interval on a Slow Serial Link to Reduce Overhead

A branch office connects to the head office via a slow 128 kbps serial link. The default 5-second hello interval consumes too much bandwidth, so the engineer increases the interval to 30 seconds to reduce control traffic.

Topology

Branch(R1)---128kbps Serial---(R2)HQ R1(Serial0/0/0)---10.0.0.0/30---(Serial0/0/0)R2

Steps

  1. 1.Step 1: Enter global configuration mode: R1# configure terminal
  2. 2.Step 2: Enter interface configuration mode for Serial0/0/0: R1(config)# interface Serial0/0/0
  3. 3.Step 3: Set the EIGRP hello interval to 30 seconds for AS 100: R1(config-if)# ip hello-interval eigrp 100 30
  4. 4.Step 4: Adjust the hold time to 90 seconds (3x hello): R1(config-if)# ip hold-time eigrp 100 90
  5. 5.Step 5: Exit configuration mode: R1(config-if)# end
Configuration
!
interface Serial0/0/0
 ip address 10.0.0.1 255.255.255.252
 ip hello-interval eigrp 100 30
 ip hold-time eigrp 100 90
!

Verify: Use 'show ip eigrp 100 interfaces Serial0/0/0 detail' and verify 'Hello interval is 30 sec' and 'Hold time is 90 sec'.

Watch out: On serial links, the default hello interval is 5 seconds (not 60) unless the interface is configured as multipoint. Ensure the interface type is correct; otherwise, the default may already be 5 seconds.

Troubleshooting with This Command

When troubleshooting EIGRP neighbor issues, the `ip hello-interval eigrp` command is often examined to ensure consistency between neighbors. A common symptom is that EIGRP neighbors fail to form or flap intermittently. Healthy output from `show ip eigrp interfaces detail` shows the configured hello interval and hold time.

If the hello interval is mismatched between two routers, they can still form adjacency because EIGRP uses the hold time from received hello packets; however, if the hold time is too short relative to the hello interval, neighbors may time out. For example, if Router A has a hello interval of 5 seconds and hold time of 15 seconds, and Router B has a hello interval of 30 seconds with hold time of 90 seconds, Router A will receive hellos every 30 seconds but its hold time is only 15 seconds, causing Router A to declare Router B dead after 15 seconds of no hello. The key is to ensure that the hold time on each router is greater than the hello interval of its neighbor.

A diagnostic flow: 1) Check neighbor state with `show ip eigrp neighbors`. If neighbors are missing or in 'Pending' state, check interface configuration. 2) Use `show ip eigrp interfaces detail` to view hello and hold timers on both sides. 3) Compare the values; if one side has a very short hold time (e.g., 15 seconds) and the other sends hellos every 30 seconds, the neighbor will flap. 4) Use `debug eigrp packets hello` to see hello packet exchange; if hellos are not received at expected intervals, check for Layer 1/2 issues or ACLs blocking EIGRP (protocol 88). 5) Correlate with `show ip eigrp topology` to see if routes are missing. The `ip hello-interval eigrp` command itself is not a troubleshooting command but a configuration one; however, verifying its effect is crucial.

Also, note that the command is per-AS; if multiple EIGRP processes run on the same interface, each can have its own hello interval. In summary, mismatched hello/hold timers are a common cause of EIGRP instability, and the `ip hello-interval eigrp` command is the tool to adjust them.

CCNA Exam Tips

1.

CCNA exam tip: The default hello interval is 5 seconds on LAN interfaces and 60 seconds on NBMA (e.g., Frame Relay) interfaces.

2.

CCNA exam tip: The hold time is automatically set to 3 times the hello interval, but can be changed independently with 'ip hold-time eigrp'.

3.

CCNA exam tip: If you change the hello interval, the hold time adjusts automatically only if not manually configured.

4.

CCNA exam tip: Mismatched hello or hold times can prevent EIGRP neighbor adjacency from forming.

Common Mistakes

Mistake: Changing hello interval without adjusting hold time, causing neighbor flapping if hold time is too short.

Mistake: Setting hello interval too low on slow links, causing excessive hello traffic and CPU load.

Mistake: Forgetting to apply the command on the correct interface or using the wrong AS number.

ip hello-interval eigrp [as] [secs] vs ip hold-time eigrp [as] [secs]

The ip hello-interval eigrp and ip hold-time eigrp commands are often considered together because they control the frequency of EIGRP hello packets and the timeout for neighbor loss, respectively. Both are configured under interface configuration mode and directly influence EIGRP neighbor adjacency stability and convergence speed.

Aspectip hello-interval eigrp [as] [secs]ip hold-time eigrp [as] [secs]
Default value5 seconds (NBMA: 60 seconds)15 seconds (NBMA: 180 seconds)
EffectSets how often hello packets are sentSets the time to wait for a hello before declaring neighbor down
RelationshipHold time should be ≥ 3× hello interval (recommended)Hold time is typically 3× hello interval by default
Impact on convergenceShorter interval speeds up neighbor detection and convergenceShorter hold time reduces failure detection time but may increase flapping
Verificationshow ip eigrp interfaces [interface]show ip eigrp neighbors [interface]

Use ip hello-interval eigrp [as] [secs] when you need to adjust the frequency of hello packets, typically to speed up convergence on high-speed links or reduce overhead on slow links.

Use ip hold-time eigrp [as] [secs] when you need to control the timeout for neighbor loss, such as to prevent flapping on unreliable links or to align with a modified hello interval.

Platform Notes

In IOS-XE, the command syntax and behavior are identical to classic IOS. The output of `show ip eigrp interfaces detail` includes the hello interval field. In NX-OS, the equivalent command is `ip hello-interval eigrp <instance-tag> <seconds>` under interface configuration mode, where the instance-tag replaces the AS number.

For example: `interface ethernet 1/1; ip hello-interval eigrp 100 5`. NX-OS also supports the `ip hold-time eigrp` command. In IOS-XR, the command is not directly available; instead, EIGRP timers are configured under the EIGRP router configuration using `timers hello-interval <seconds>` for all interfaces or per-interface using `interface <type> <id> timers hello-interval <seconds>`.

For ASA devices, EIGRP is not supported; the ASA uses OSPF or RIP. In older IOS versions (12.x), the command is the same, but the default hello interval for low-speed interfaces (e.g., 56k) was 60 seconds; in 15.x and 16.x, the default is still 5 seconds for most interfaces, but the 60-second default applies only to multipoint interfaces like Frame Relay. There are no significant syntax differences between IOS versions.

Always verify the interface type to understand the default hello interval before modifying it.

Related Commands

ip hold-time eigrp [as] [secs]

Configures the EIGRP hold time (in seconds) for a specific EIGRP autonomous system on an interface, determining how long the router waits for a hello packet before declaring the neighbor down.

show ip eigrp interfaces

Displays detailed information about interfaces on which EIGRP is enabled, including neighbor status, pending routes, and interface statistics, used to verify EIGRP adjacency and interface participation.

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.

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