Fat-Tree Topology Validation

This section specifies the options for Fat-Tree topology validation. Topology validation checks that the provided topology is a properly connected Fat-Tree topology. It detects tree structure, its “connectivity groups” and neighborhoods and their link issues. It also reports on a network theoretical “bisectional” bandwidth.

A newly generated output file – ibdiagnet2.fat_tree contains details about switches uplinks/downlinks issues and tree structure by levels. In a case FLIDs were applied on the network the output could contain warning if the same FLID appears in some neighborhoods.

Parameter	Description
--ft	Provides a report of the fabric Fat-Tree analysis. Data will be dumped to the ibdiagnet2.fat_tree file. Warnings and errors will be dumped to the ibdiagnet2.log and ibdiagnet2.fat_tree files.
--ft_roots_regex_opt	The regular expression to select Fat-Tree root nodes. Only nodes matching the regular expression will be taken as roots.
--smdb <file>	Loads Fat-Tree roots from the subnet manager SMDB file (the routing engine reported in opensm-smdb.dump file should be one form the following list: “Fat-Tree”, Adaptive Routing Fat-Tree”, “UPDN”, “Adaptive Routing UPDN”).

Parameter

Description

--ft

Provides a report of the fabric Fat-Tree analysis.

Data will be dumped to the ibdiagnet2.fat_tree file.

Warnings and errors will be dumped to the ibdiagnet2.log and ibdiagnet2.fat_tree files.

--ft_roots_regex_opt

The regular expression to select Fat-Tree root nodes. Only nodes matching the regular expression will be taken as roots.

--smdb <file>

Loads Fat-Tree roots from the subnet manager SMDB file (the routing engine reported in opensm-smdb.dump file should be one form the following list: “Fat-Tree”, Adaptive Routing Fat-Tree”, “UPDN”, “Adaptive Routing UPDN”).

Example:

ibdiagnet –-ft

ibdiagnet's Output:

 Fat-Tree Topology Validation
-I- Fat-Tree topology detection finished successfully

-I- 2 level Fat-Tree was discovered:
         rank: 0(Roots) #switches: 4
         rank: 1 #switches: 4

-I- Fat-Tree topology validation finished successfully
-E- For more errors see the dump file: ibdiagnet2.fat_tree
-I- Calculated Fat-Tree bisectional bandwidth: 800.00 [Gb/s]

fat_tree file “connectivity groups”/neighborhoods and their switches uplinks/downlinks issues details:

-I- Neighborhood 0: all spines have the same number of downlinks: 4
-I- Neighborhood 0: all lines have the same number of uplinks: 4
-W- Neighborhood 0: lines with different number of downlinks (expected  4 downlinks)
         2 downlinks: BM1-2 BM1-1

fat_tree file tree structure - switches by rank:

rank: 0 (Roots)size: 4
        BM0-2
        BM0-0
        BM0-1
        BM0-3

rank: 1 (Leaves)size: 4
        BM1-0
        BM1-2
        BM1-1
        BM1-3

fat_tree file tree structure – “connectivity groups”/neighborhoods by rank

on ranks (0, 1) -- neighborhoods: 1
        neighborhood: 0
                spines: 4 switches
                        BM0-2
                        BM0-0
                        BM0-1
                        BM0-3
                lines: 4 switches
                        BM1-0
                        BM1-2
                        BM1-1
                        BM1-3

fat_tree file - the same FLID is found in some neighborhoods
```
-W- FLID=155 appears in the following neighborhoods: 1, 3
```

Last updated: June 03, 2026