Reading through this block, it feels like lines 289-293 should be extracted to a private method:

static parseDevice(final String line) {
     final String[] tokens = line.split( " ");
     if (tokens != null && tokens.length < 2) {
        return "";
     }

     final String device = tokens[2];
     return Strings.isNullOrEmpty(device) : " " ? device;
} 

The extraction of this method would not only shorten the deleteExitingLinkLocalLocalRoutetTable method, but clearly express the intent. It also allows a unit test to be written to verify that parsing works as expected for different types of input.

With respect to this specific code, I would like do this the next time we do a round of refactoring, possibly factor such code to a util class that can be used as a general purpose line parsing static method and add unit tests. For now, at least the code takes care of malformed inputs.