Try:

Code:

awk '{  split($1, f, /,/)
        if((f[2]","f[1]) in o) next
        o[$1]
        print
}' input

As always, if you are using a Solaris/SunOS system, use /usr/xpg4/bin/awk or nawk instead of awk.

Note that this won't skip an input line if the 1st field contains the same two nodes in the same order; it will just skip the line if the 1st field contains the same two nodes in reverse order. This script will also skip lines even if the second field contains a different value than the previously printed entry. If this isn't what you want, you need to give more complete requirements.