How do I implement a hierarchy of CSIRTs?

There are two ways: By referencing different irt objects in the inetnum-hierarchy. In the following example the inetnum object UK-V4 references the IRT-UK: The larger inetnum object UNIVIE references the IRT-ACOnet-CERT:

meijer@gebbetje:~$ whois -h whois.ripe.net -r -c  131.130.0.0
% This is the RIPE Whois server.
% The objects are in RPSL format.
%
% Rights restricted by copyright.
% See http://www.ripe.net/ripencc/pub-services/db/copyright.html

inetnum:      131.130.0.0 - 131.130.255.255
netname:      UNIVIE
descr:        LAN University of Vienna
country:      AT
admin-c:      HS118
tech-c:       UVNA1-RIPE
mnt-by:       AS760-MNT
mnt-irt:      IRT-ACOnet-CERT
status:       ASSIGNED PI
changed:      porten _at_ mvs.gmd _dot_ de 19900816
changed:      dfk _at_ cwi _dot_ nl 19900917
changed:      Ewald.Jenisch _at_ cc.univie.ac _dot_ at 19930315
changed:      ripe-dbm _at_ ripe _dot_ net 20000225
changed:      woeber _at_ cc.univie.ac _dot_ at 20010626
changed:      panigl _at_ cc.univie.ac _dot_ at 20010629
source:       RIPE

meijer@gebbetje:~$ whois -h whois.ripe.net -r -c 131.130.7.33
% This is the RIPE Whois server.
% The objects are in RPSL format.
%
% Rights restricted by copyright.
% See http://www.ripe.net/ripencc/pub-services/db/copyright.html

inetnum:      131.130.7.32 - 131.130.7.47
netname:      UK-V4
mnt-irt:      IRT-UK
descr:        LAN Ulrich Kiermayr
country:      AT
admin-c:      UK6107-RIPE
tech-c:       UK3
mnt-by:       AS760-MNT
mnt-by:       UK-MNT
status:       ASSIGNED PA
changed:      ulrich.kiermayr _at_ univie.ac _dot_ at 20020822
source:       RIPE


Another way would be to reference multiple irt objects in the most specific inetnum object, but that does not convey how the hierarchy is made up. This is the only way if there is no IP hierarchy that is usable for this purpose. This might occur with legacy class B/C addresses where one constituent might want to add his own irt object as well as the one of the NREN/LIR and the LIR does not also control the less-specific. Then the only way is for you to use both irt objects.