S.H.
6 months old is a "growth spurt" time for babies. Also at 9 months, and 12 months and so forth, about every 3 months.
At these times, they get hungrier, feed more, and more frequently...so you need to feed him even if that means waking up. They are changing physically, cognitively and in terms of their abilities. Also, teething may start to occur as well, which wakes them too.
It could be that he is also waking due to all the changes they are going through. It is normal, and a phase. I would not do the CIO method, at times like this. It's developmental based probably. Normal stuff.
I know it's tiring..but they all go through this. His sleep/wake patterns WILL change, as they go through growth changes and spurts, and teething and so forth. But, if you keep a constant routine pre-bed and keep it constant... that WILL help them get into a routine.
Both my kids went through this as well...it's temporary, it is a phase and passes. Just keep to your same bed times as well... since that is his routine. As they go through the growth phases, it will subside. Keep in mind, that these developmental changes are not necessarily easy for them either....they have so much to get used to. They grow up quickly and will soon no longer be babies anymore... take heart and offer comfort to him as needed.
As he gets more mobile as well, sitting up, rolling over, pulling up, standing...all of these developmental changes will cause a glitch in their sleep patterns often times. All part of ages and stages and phases. It will wake them. Babies sleep patterns are not static...it will grow and change as they mature as well. Even adults don't have the same sleep patterns since we were kids. It ebbs and flows. BUT, routine and consistency with sleep habits DOES help.... down the road.
There are so many approaches.
My son went through those same sleep changes/patterns as well at that age. But it subsides... now at 21 months old, he does sleep through the night about 90% of the time. But it is not the same everyday. Make sure he takes naps too...over tired babies actually do NOT sleep well.
All the best,
~Susan