'List routers
:rtype ``list`` of :class:`CloudStackRouter`'

def ex_list_routers(self, vpc_id=None):

    args = {}
    if (vpc_id is not None):
        args['vpcid'] = vpc_id
    res = self._sync_request(command='listRouters', params=args, method='GET')
    rts = res.get('router', [])
    routers = []
    for router in rts:
        routers.append(CloudStackRouter(router['id'], router['name'], router['state'], router['publicip'], router['vpcid'], self))
    return routers
