If we were being superficial about the analysis of regional integration, we'd probably say that Nigeria is to ECOWAS, as Sudan is to IGAD.
In fact, that superficial analysis has some elements of truth in it, in the sense that just as Nigeria is the most populous countries in Africa, Sudan , as wikipedia says of it that it is:
the largest African country by area.  The country is situated at a crossroads between the Horn of Africa and the Middle East. It is bordered by Egypt to the north, the Red Sea to the northeast, Eritrea and Ethiopia to the east, Kenya and Uganda to the southeast, Democratic Republic of the Congo and the Central African Republic to the southwest, Chad to the west, and Libya to the northwest. It is the tenth largest country in the world.
So, basically, they're both big.
Even in regional integration, size matters, because the bigger you are, the more clout--ostensibly--you have. Nigeria has oil, and some challenges; Sudan has...Darfur.
You would have thought if Nigeria is a de facto hegemon (by its sheer size), Sudan would correspondingly be considered one, too.
It's therefore puzzling--at first--to read, as I read here in Africa News that the comparatively smaller country of Kenya, which is a key country in the East African Community, is going to be the peacemaker, mediating in the Eritrea-Somalia-Ethiopia crisis.
Simple point is that: Kenya is currently chairing the 26th session of an IGAD inter-ministerial, so perhaps it doesn't have a choice, as it suggested here:
Kenyan Foreign Minister Raphael Tuju, whose country chairs IGAD, afterward said the bloc had "no appetite" to mediate Eritrea and Ethiopia's feud despite the problems it has caused in the region and within IGAD.
"The problem between Ethiopia and Eritrea is like a problem between brothers. Our hands are pretty full at the moment so it is not one of the things we have an appetite to get into."
Quite whether the problem between Ethiopia and Eritrea can be simplistically analogous to a problem between brothers is a moot point. Either way, for now, Kenya is the peacemaker.
At the heart of the Ethiopian-Eritrea dispute is a finger-pointing from Somalia and the United States that Eritrea...:
...was supporting insurgents in Somalia to fight its neighbour Ethiopia. Eritrea and Ethiopia fought a two-year border war whose effects are still lingering (from:http://www.africa-interactive.net/index.php?PageID=4181)
The article maintains:
Eritrea is said to be demanding the urgent withdrawal of Ethiopian forces from Somalia, but IGAD's six other member States are calling for quick deployment of the African troops before the Ethiopian pullout.
"We have discussed this issue previously and Ethiopia has been willing to withdraw from Somalia but we all agree that it has to be a tactful pullout otherwise it would plunge the region into a security vacuum," Tuju explained
As nature abhors a vacuum, it might be rather critical to start consolidating existing peace efforts to have that intractable dispute between regional neighbours sorted.
West Africa is very familiar with this type of situation, with ECOWAS having resolved potentially-explosive situations in Liberia and Sierra Leone in the 20th century.
Today, we have the regional hegemon of ECOWAS that is Nigeria voting in polls. Despite elements and pockets of violence here and there, AFP, through africasia news has said
An observer team from the west African bloc ECOWAS said Saturday's state elections were "relatively free and peaceful," the News Agency of Nigeria reported Monday
I am personally confident about moves by Kenya on the dispute. I can foresee that the experience that the six-member IGAD is obtaining is heading it towards a conflict resolution and conflict management imperative, such as that was experienced in ECOWAS--and that cannot, surely, be a bad thing, as far as human resource goes for building well-experienced Africans' capacity for the bigger project of African unity.