Cisco IOS XR Bundle Troubleshooting Guide: LACP, MLAG & BFD

Link bundles are the backbone of high-availability service provider networks, yet when a bundle member refuses to distribute traffic or an LACP negotiation silently fails, the root cause is often buried in configuration conflicts rather than hardware faults. This guide, distilled from Cisco's own IOS XR troubleshooting knowledge base, walks through the architecture of bundle-ether interfaces, common failure signatures, and the exact CLI commands needed to isolate them. It covers standard LACP behavior, BFD over bundle members, and multichassis LAG (MC-LAG) with ICCP. Whether you run ASR 9000 or NCS platforms, these verification steps apply to any IOS XR release that supports link aggregation.

What Is an IOS XR Link Bundle?

On Cisco IOS XR, a bundle aggregates multiple physical interfaces in a Layer 2 manner based on IEEE 802.1ax/802.1ad. The bundle is treated as a single interface by upper-layer protocols (one MAC, one IP, one configuration set) and is also known as EtherChannel, Port-Channel, or LAG. All features are applied on the bundle interface and replicated to the NPUs that hold its members, and members can reside on multiple line cards.

Key Bundle Concepts

• L3 hashing uses source IP, destination IP and router ID; TCP/UDP ports are included for packet hashing.
• L2 hashing uses source MAC, destination MAC and router ID.
• LACP has three modes: active, passive, or ON (no LACP), with short (1s) or long (30s) control-packet intervals.
• Minimum/maximum active member links can be enforced on the bundle interface.

Common Problems and How to Fix Them

1. Bundle Interface Does Not Come Up

Check the bundle interface and all members are in no shutdown state, verify the remote side is up, and confirm the port MAC address is valid. When LACP is used, both sides must have identical LACP parameters:

show lacp bundle
show lacp counters
clear lacp counters
debug bundlemgr local packets port <x>

2. Bundle Members Are Not Distributing

A member that is up but not distributing is a classic LACP state mismatch. Run show bundles reasons to see exactly why the member is excluded, then confirm all members share the same speed, media and peer characteristics with show running interface.

3. Adding a Member Fails with Commit Error

When adding an interface to a bundle, the member must be clean — no IP address, no subinterfaces. Otherwise the commit is rejected atomically:

% Failed to commit one or more configuration items during an atomic operation
!!% Bundle membership configuration conflicts with underlying physical link configuration

Remove the conflicting configuration, then retry bundle id <x> mode active and commit.

4. L3 Traffic Is Not Flowing

Verify ARP is resolved on all bundle line cards and that the bundle MAC in show arp matches show bundle. Hash-based drops such as EGR-LAG-NOT-LOCAL-MEMBER can be inspected with show controller bundle bundle-ether<id> location <x>.

BFD over Bundle Members (BFDoBM)

BFD over Bundle Members is an enhancement to fast Layer 3 protection that determines whether a bundle member can carry traffic. BFD sessions start only after a member reaches LACP DISTRIBUTING state, and BFD status does not affect the LACP state of the link. Two modes exist: Async (both sides exchange BFD packets) and Echo (packets loop through the peer's forwarding path).

MC-LAG with ICCP for Dual-Homed Customers

Multichassis LAG lets two IOS XR devices appear as a single LAG to a dual-homed customer edge device. The two provider edges (POAs) exchange state over an LDP link using the Inter-Chassis Communication Protocol (ICCP). Only one POA forwards traffic at a time; on failure the devices manipulate LACP states to switch over. Key verification commands:

show iccp counters
show iccp trace
show mlacp inconsistencies
show bundle reasons

Full Troubleshooting Toolkit

show bundle
show bundle status
show lacp system-id
admin show diag chassis eeprom-info
show tech-support bundle file <filesystem:filename>

For more IOS XR troubleshooting practice, see our guides on input drops on IOS XR routers and interface CRC error diagnosis.

原文链接：https://community.cisco.com/t5/service-providers-knowledge-base/troubleshooting-guide-ios-xr-bundles/ta-p/3152265