Use the following CLI syntax to configure IMA bundle parameters:
configure# port bundle-type-slot/mda.bundle-num
— description description-string
— multilink-bundle
— fragment-threshold value
— ima
— atm
— cell-format {uni | nni}
— min-vp-vpi vp-vpi-value
— exit
— link-delay {activate |deactivate} milli-seconds
— max-bandwidth number-links
— version ima-version
— red-differential-delay red-diff-delay down
— member port-id
Configuration notes:
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 those common IMA group interface characteristics:
Encapsulation type (ATM)
ATM interface characteristics (under the ATM menu context)
Interface mode type (only access is supported)
MTU value (derived from the primary link)
Member links inherit those common characteristics from the IMA group that they are part of and as long as they are part of an IMA group. Characteristics derived from the primary link (MTU, interface mode type) can be changed on the primary link only and not on other links in the bundle or a bundle itself. The primary link is the member which has the lowest ifindex. When a member is added/deleted, the primary member may be changed based on the ifIndicies of all member links.
After 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 bundle characteristics enforced over the link. Note that when a link is removed from an IMA bundle, the link's ATM characteristics are reset to ATM interface defaults.
No services can be configured on the member link itself.
After the primary member has been added each additional member added to the group is only accepted if it matches the configuration of the IMA group. ATM interface characteristics are not part of this verification as they are overwritten/reset to defaults when a link is added to/removed from an IMA bundle.
Upon addition to an IMA group, each added member is automatically assigned an IMA link ID. IMA link IDs are in range from 0 to 7 and stay constant as long as the router does not reboot.
When configuring IMA bundles, consider the following guidelines:
IMA bundles should contain at least two members.
A maximum of eight members can be included in an IMA bundle.
IMA links can only be aggregated into a bundle within a single MDA.
IMA group maximum bandwidth and minimum link settings allows, by default, for over-subscription of shaped services; however when that occurs scheduling of traffic over an IMA group ATM interface degrades to round-robin between shaped services therefore, to preserve full ATM TM even during a member link failure, it is recommended that maximum bandwidth is set to minimum links.
When configuring the red differential delay for IMA groups on ASAP MDAs, the value configured is converted into acceptable frame sequence number delay on a link because delay is granular to IMA frame sequence number difference. For E1 channels (receiving frame time 27 ms), configured values map to the enforced values as follows: 0 ms maps to 0 frame sequence number difference (27 ms delay), 1 to 27 ms maps to 1 frame sequence number difference (54 ms delay), 28 - 50 ms maps to 2 frame sequence number difference (81 ms delay). Similarly, for DS1 channels (receiving frame time 35 ms), configured values map to enforced values as follows: 0 ms maps to 0 frame sequence number difference (35 ms delay), 1 to 35 ms maps to 1 frame sequence number difference (70 ms delay), 36 to 50 ms maps to 2 frame sequence number difference (105 ms delay).
When a channel is deleted from an IMA group it is recommended that a deletion takes place at the far end first when the far end supports graceful deletion to ensure no cell loss takes place on the 7750 SR RX end of the channel. When a channel is deleted on the 7750 SR end first, a small data loss takes place on the 7750 SR RX side (depending on the time required for the far end to deactivate its TX on the link being deleted).
When no member links are configured on an IMA group, the speed of an E1 channel is used to compute the maximum IMA group bandwidth that may be allocated to shaped services.
The shutdown command for IMA groups sets the IMA group state to ‟Blocking”. This makes the group operationally down but does not bring down the individual IMA links. Services configured on the IMA group go operationally down as well.
The 7750 SR supports automatic IMA version changing when the far end IMA group version matches the configured version. The group remains operationally down until one of the IMA groups changes version.
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 shows the creation of an IMA bundle with three group members residing on a channelized OC-3 ASAP MDA in slot 5/2/1:
A:ALA-A>config# port bundle-ima-5/2.1
A:ALA-A>config>port# multilink-bundle
A:ALA-A>config>port>ml-bundle# member 5/2/1.1.1.1
A:ALA-A>config>port>ml-bundle# member 5/2/1.1.2.1
A:ALA-A>config>port>ml-bundle# member 5/2/1.1.3.1