Best Practices for Managing EIGRP Bandwidth on Cisco Devices

Managing EIGRP Bandwidth with ip bandwidth-percent

When configuring Enhanced Interior Gateway Routing Protocol (EIGRP) on Cisco routers, it is essential to control how much interface bandwidth is consumed by routing updates. This is especially important on low-bandwidth or congested links, where excessive control traffic can negatively affect application performance.

In this post, we explore how to manage EIGRP bandwidth usage using the ip bandwidth-percent command, examine differences across IOS versions, and compare EIGRP’s approach with OSPF bandwidth tuning.

For a comprehensive overview of EIGRP, refer to the Wikipedia article on EIGRP .

---

Controlling Bandwidth Usage for EIGRP

EIGRP uses a portion of the interface’s configured bandwidth to send routing updates. By default, EIGRP limits itself to 50% of the interface bandwidth. This behavior can be adjusted using the following interface-level command:

ip bandwidth-percent eigrp <AS-number> <percentage>

• AS-number: Autonomous System number of the EIGRP process
• Percentage: Maximum bandwidth EIGRP is allowed to consume

Example Configuration

Router1# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router1(config)# interface Serial0/1
Router1(config-if)# ip bandwidth-percent eigrp 100 40
Router1(config-if)# end
Router1#

In this example, EIGRP is restricted to using no more than 40% of the interface bandwidth for routing updates.

---

Checking Interface Bandwidth

Router1# show interface Serial0/1
Serial0/1 is up, line protocol is up
  Hardware is HD64570
  Internet address is 10.1.1.1/30
  MTU 1500 bytes, BW 1544 Kbit/sec, DLY 20000 usec
  Encapsulation HDLC

Viewing EIGRP Traffic Statistics

Router1# show ip eigrp traffic
EIGRP-IPv4 Traffic Statistics for AS 100
  Hellos sent/received: 145 / 140
  Updates sent/received: 20 / 18
  Queries sent/received: 3 / 3
  Replies sent/received: 3 / 3

These outputs help confirm that EIGRP is functioning correctly and allow you to monitor control-plane traffic after bandwidth adjustments.

---

Syntax and Behavior Differences Across IOS Versions

Key Differences

• Subinterface Support: Older IOS versions may behave inconsistently on subinterfaces, while newer versions support reliable subinterface-level control.
• Bandwidth Calculation: Older IOS versions rely on default interface bandwidth values unless manually set. Newer IOS versions automatically factor in updated bandwidth settings.
• Precision: Newer IOS versions allow finer-grained bandwidth allocation. Older versions support only whole-number percentages.
• Dynamic Adjustment: Recent IOS releases apply changes dynamically without dropping neighbors. Older versions may briefly reset EIGRP adjacencies.

---

Comparison with OSPF Bandwidth Tuning

Feature	EIGRP	OSPF
Bandwidth Control Method	ip bandwidth-percent eigrp	Indirect (Hello/Dead timers)
Default Bandwidth Usage	50% of interface bandwidth	No fixed percentage
Granular Control	Yes (percentage-based)	Limited
Effect on Adjacencies	Minimal (new IOS)	Timer changes may reset neighbors
Low-Bandwidth Optimization	Excellent	Moderate

Unlike EIGRP, OSPF does not provide a direct mechanism to limit bandwidth usage. Instead, OSPF tuning relies on adjusting hello and dead intervals, which indirectly influences protocol traffic but can impact convergence time.

---

Best Practices

• Set Accurate Interface Bandwidth: Always configure the correct interface bandwidth using the bandwidth command before tuning EIGRP.
• Monitor After Changes: Use show ip eigrp traffic and show interface to validate behavior.
• Use Subinterfaces Carefully: Apply bandwidth limits per subinterface on multipoint links.

---

Final Thoughts

Properly managing EIGRP bandwidth usage is critical for maintaining predictable network performance, especially on low-speed or shared links. The ip bandwidth-percent command provides precise and effective control, making EIGRP particularly well-suited for constrained environments.

Have you encountered challenges while configuring EIGRP bandwidth limits? Share your experience in the comments and help others learn from real-world deployments.