ipForwarding R/W ?

Hi,
 
I'm trying to test the snmpset on ipForwarding OID and I get a
"notWritable" error.
The snmpget is working fine. See the details bellow:
 
snmpget -v2c -cxxx localhost ipForwarding.0
IP-MIB::ipForwarding.0 = INTEGER: notForwarding(2)
 
snmpset -v2c -cxxx localhost IP-MIB::ipForwarding.0 i 1
Error in packet.
Reason: notWritable (That object does not support modification)
Failed object: IP-MIB::ipForwarding.0
 
This is surprising since ipForwarding is defined in  IP-MIB as R/W
object:
 
ipForwarding OBJECT-TYPE
    SYNTAX      INTEGER {
                    forwarding(1),    -- acting as a router
                    notForwarding(2)  -- NOT acting as a router
                }
    MAX-ACCESS  read-write
    STATUS      current
    DESCRIPTION
            "The indication of whether this entity is acting as an IP
            router in respect to the forwarding of datagrams received
            by, but not addressed to, this entity.  IP routers forward
            datagrams.  IP hosts do not (except those source-routed via
            the host)."
    ::= { ip 1 }
 
Could someone explain this behavior?
 
Thanks,
Eugen