ProblemAIX EtherChannel support with LLT for VCS version 4.0MP3, 4.0MP4 and 5.0MP1
1. How do we configure the EtherChannel device for use with LLT?
This procedure is taken from the IBM Red Book "AIX 5L Networks and communication management" and is modified to show the correct way to configure an EtherChannel device for use with LLT:
1. Type "smitty etherchannel" at the command line.
2. Select Add an EtherChannel / Link Aggregation from the list and press Enter.
3. Select the primary Ethernet adapters that you want on your EtherChannel and press Enter. If you are planning to use EtherChannel backup, do not select the adapter that you plan to use for the backup at this point. The EtherChannel backup option is available in AIX 5.2 and later.
Note: The Available Network Adapters displays all Ethernet adapters. If you select an Ethernet adapter that is already being used (has an interface defined), you will get an error message. You first need to detach this interface if you want to use it.
4. Enter the information in the fields according to the following guidelines:
o Parent Adapter: Provides information of an EtherChannel's parent device (for example, when an EtherChannel belongs to a Shared Ethernet Adapter). This field displays a value of NONE if the EtherChannel is not contained within another adapter (the default). If the EtherChannel is contained within another adapter, this field displays the parent adapter's name (for example, ent6). This field is informational only and cannot be modified. The parent adapter option is available in AIX 5.3 and later.
o EtherChannel / Link Aggregation Adapters: You should see all primary adapters that you are using in your EtherChannel. You selected these adapters in the previous step.
o Enable Alternate Address: Setting this to yes will enable you to specify a MAC address that you want the EtherChannel to use. If you set this option to no, the EtherChannel will use the MAC address of the first adapter. Set this to "yes"
o Alternate Address: Specify the MAC address that you want to use here. The address you specify must start with 0x and be a unique 12-digit hexadecimal address (for example, 0x001122334455).
5. Please do not enable jumbo frames as this may impact performance.
2. Why do we need to set the MAC address manually?
When you set the alternate MAC address for etherchannel using smit, the EtherChannel device is assigned the MAC address you chose. The EtherChannel device will continue using this MAC address if any adapters are added or deleted. Furthermore, it means that there is no temporary loss of connectivity when adding or deleting adapters because none of the adapters "owns" the EtherChannel's MAC address.
3. What happens when you don't set the MAC address manually using smit?
If you are not using an alternate address and you plan to delete the adapter whose MAC address was used for the EtherChannel (the MAC address used for the EtherChannel is "owned" by one of the adapters), the EtherChannel will use the MAC address of the next adapter available. In other words, the one that becomes the first adapter after the deletion, or the backup adapter in case all main adapters are deleted. For example, if an EtherChannel has main adapters ent0 and ent1 and backup adapter ent2, it uses by default ent0's MAC address (it is then said that ent0 "owns" the MAC address). If ent0 is deleted, the EtherChannel then uses ent1's MAC address. If ent1 is then deleted, the EtherChannel uses ent2's MAC address. If ent0 is later re-added to the EtherChannel, it continues to use ent2's MAC address because ent2 is now the owner of the MAC address. If ent2 were then deleted from the EtherChannel, it starts using ent0's MAC address again. This will cause performance issues since LLT needs to know what the correct MAC address is in order to transmit packets.
4. When will LLT support for detecting MAC address dynamically?
We have added support to dynamically detect the MAC address in VCS versions 5.5 and 5.0MP3
5. Do I need to reboot the node for the changes to take effect?
Yes, you do need to reboot for the changes to take effect.
6. How do I check if the configuration works
Set the alternate MAC address for etherchannel and reboot the node. When the node comes back up run "lltstat -nvv" to verify the alternate MAC is configured.
Disable one of the links aggregated under etherchannel. LLT will not notice a failure and will continue to function as expected.
If the alternate MAC address is not set, LLT will experience hangs and link failures.