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About Merging Interfaces

Consider the following guidelines when you merge interfaces:

• You can merge two interfaces, which can be on different routers.
• The data collection period for the interfaces can contain gaps.
• If you merge interfaces that have overlapping time frames, the overlapping data is discarded. Precedence is given to the newer interface--that is, the interface that has the later start date.

  For example, suppose you merge Interface A and B. Interface A has collected data that starts at 1:00 P.M. and ends at 5:00 P.M. on the same day. The data collected for Interface B starts at 3:00 P.M. The merged data consists of Interface A data from 1:00 to 3:00 P.M. and Interface B data from 3:00 P.M. onward.

• You cannot merge interfaces that started collecting data at the same time.

Example

For example, suppose that your 512-Kbps link that has been running for a year is upgraded to a T1 link (a 1.54-Mbps link). Using the new T1 link causes the interface ifindex to change. For example, the previous ifIndex of 5 changes to 13--the next available ifindex for the T1 link. Other settings are changed or created, such as the ifdescr and ifAlias settings.

These changes cause the program to see the interface as a new interface. You enable the new interface so the program can collect its data.

At this point, the history of the interface is divided. To unify the history, you merge the two versions of the interface. After the merge, the history includes the data that was collected previously from the interface on the slower link and the data from the interface on the new link. The data is combined end-to-end with no overlaps or duplication.