- New and Changed Information
- Preface
- Overview
- Tools
- Installation
- Licenses
- Upgrade
- High Availability
- VSM and VEM Modules
- L3Sec
- Ports
- Port Profiles
- Port Channels and Trunking
- Layer 2 Switching
- VLANs
- Private VLANs
- NetFlow
- ACLs
- Quality of Service
- SPAN
- Multicast IGMP
- DHCP, DAI, and IPSG
- Storm Control
- System
- Before Contacting Technical Support
- Network Segmentation Manager
- VXLANs
- VSI Discovery and Configuration Protocol
- Cisco TrustSec
- vCenter Plug-in
- Ethanalyzer
Port Channels and Trunking
This chapter describes how to troubleshoot port channels and trunking and includes the following sections:.
Information About Port Channels and Trunking
This section includes the following topics:
Port Channel Overview
Port channels aggregate multiple physical interfaces into one logical interface to provide higher bandwidth, load balancing, and link redundancy.
A port channel performs the following functions:
- Increases the aggregate bandwidth on a link by distributing traffic among all functional links in the channel.
- Load balances across multiple links and maintains optimum bandwidth usage.
- Provides high availability. If one link fails, traffic previously carried on this link is switched to the remaining links. If a link goes down in a port channel, the upper protocol is not aware of it. To the upper protocol, the link is still there, although the bandwidth is diminished. The MAC address tables are not affected by link failures.
Port Channel Restriction
Trunking Overview
Trunking, also known as VLAN trunking, enables interconnected ports to transmit and receive frames in more than one VLAN over the same physical link.
Initial Troubleshooting Checklist
Use the following checklist to begin troubleshooting port channel and trunking issues:
The following commands help you to troubleshoot port channels and trunking:
- show port-channel summary
- show port-channel internal event-history interface port-channel channel-number
- show port-channel internal event-history interface ethernet slot-number
- show system internal ethpm event-history interface port-channel channel-number
- show system internal ethpm event-history interface ethernet slot-number
- show vlan internal trunk interface ethernet slot-number
- show vlan internal trunk interface port-channel channel-number
- debug port-channel error
- module vem module-number execute vemcmd show port
- module vem module-number execute vemcmd show pc
- module vem module-number execute vemcmd show trunk
Example 11-1 shows output of the show port-channel summary command.
Example 11-1 show port-channel summary Command
Troubleshooting Asymmetric Port Channels
When you are troubleshooting asymmetric port channels, follow these guidelines:
- Use APC when you want to configure a port channel whose members are connected to two different upstream switches.
- APC depends on Cisco Discovery Protocol (CDP). Make sure CDP is enabled on the VSM and upstream switches.
- Physical ports within an APC get assigned subgroup IDs based on the CDP information received from upstream switches.
- A user can manually configure subgroup IDs in interface configuration submode.
- Make sure that you configured subgroup CDP either with a port profile or on the port channel interface.
- Ports in APC come up only when they are assigned subgroup IDs manually or through CDP.
- Enter the show cdp neighbors command on the VSM and check the output.
- Once the ports came up, check that ports are put in the correct subgroups by entering the module vem module-number execute vemcmd show pc command on the VEM.
- Use the debug port-channel trace command to collect information.
Cannot Create Port Channel
Newly Added Interface Does Not Come Online In a Port Channel
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Newly added interface does not come online in a port channel. |
1. Make sure that you have the port channel configuration in the port profile (port group) used by that interface. 2. Check if a port channel is already present on the module that is using the same port profile. If there is, check the running configuration on the port channel and the newly added interface. The interface does not come up if the port channel configurations are different. 3. If the port channel configuration is different, apply the difference on the newly added interface. Remove the port, and then add it back. |
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Interface parameters are not compatible with those of the existing port. |
See the “Forcing Port Channel Characteristics onto an Interface” section, to force the physical interface to take on the parameters of the port channel. Use this procedure only if you want to configure the port channel manually and not through the port profile. |
Forcing Port Channel Characteristics onto an Interface
You can force the physical interface to take on the characteristics of the port channel. Use this procedure only if you want to configure the port channel manually and not through the port profile.
BEFORE YOUR BEGIN
DETAILED STEPS
Step 1 Enter the interface configuration mode.
You are placed into interface configuration mode.
Step 2 Force the physical interface with an incompatible configuration to join the channel group.
channel-group channel-number force
The physical interface with an incompatible configuration is forced to join the channel group.
Verifying a Port Channel Configuration
You can debug port channels configured through a port profile.
BEFORE YOUR BEGIN
DETAILED STEPS
Step 1 Verify that you have configured a port channel in the profile.
switch# show port-profile name profile-name
Step 2 Display summary port channel information.
switch# show port-channel summary
Step 3 Debug the port channel configuration.
switch# debug port-channel trace
VLAN Traffic Does Not Traverse Trunk
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Add the VLAN to the allowed VLAN list. Use the switchport trunk allowed vlan add vlan-id command in the profile used by the interface. |