ssh -L 9999:localhost:9998 dalvarado@host1 'ssh -L 9998:localhost:1234 -N dalvarado@host2'

ssh -L 9999:host2:22 user@host1

Host target.machine
User          targetuser
HostName      target.machine
ProxyCommand  ssh proxyuser@proxy.machine nc %h %p 2> /dev/null

scp file dalvarado@host1:.

ssh -t dalvarado@host1 'scp file dalvarado@host2:.'