An IMA group has common interface characteristics (for example, configuration that applies to a logical ATM interface either configured via the IMA group context or taken from the primary link). The following list details the common IMA group interface characteristics:
ATM interface characteristics (under the ATM menu context)
interface mode type (only access is supported)
Member links inherit these common characteristics from the IMA group that they are part of and as long as they are part of the IMA group.
The primary link is the member that has the lowest ifindex. When a member is added or deleted, the primary member may be changed based on the ifindexes of all member links.
Once a path becomes part of an IMA group logical link, the path ceases to exist as a physical ATM path interface. This means that:
ATM interface characteristics enforced over the link are those of a group. When a link is removed from an IMA group, the link's ATM characteristics are reset to ATM interface defaults.
no services can be configured on the member link
After the primary member has been added, each additional member added to the group will only be accepted if it matches the configuration of the IMA group.
ATM interface characteristics are not part of this verification as they are overwritten or reset to defaults when a link is added to or removed from an IMA group.
When a member is assigned to an IMA group, the member is automatically assigned an IMA link ID. IMA link IDs range from 0 to 16 and stay constant as long as the router does not reboot.
When configuring IMA groups, consider the following guidelines.
All IMA links in an IMA group must belong to the same T1/E1 adapter card or the same physical OC3 port.
IMA bundles can only be aggregated on a single adapter card.
On the 2-port OC3/STM1 Channelized Adapter card, the red differential delay is configurable from 2 to 50 ms and is accurate within 1 ms. On the 16-port T1/E1 ASAP Adapter card and 32-port T1/E1 ASAP Adapter card, the red differential delay is configurable from 2 to 75 ms and is accurate within 1 ms.
If no member links are configured on an IMA group, the speed of an E1 channel will be used to compute the maximum IMA group bandwidth that may be allocated to shaped services.
When adding member links to an IMA group, the clock-source of the E1 or DS1 link must be set to node-timed.
The following example illustrates creation of an IMA group with three group members residing on a channelized 16-port T1/E1 ASAP Adapter card in slot 1/3/1:
NOK-A>config# port bundle-ima-1/3.1
NOK-A>config>port# multilink-bundle
NOK-A>config>port>ml-bundle# member 1/3/1.1
NOK-A>config>port>ml-bundle# member 1/3/2.1
NOK-A>config>port>ml-bundle# member 1/3/3.1