The DHCP protocol allows clients to make DHCPINFORM requests, which mean (roughly) "I already have an IP address, but I would like to know all the other configuration variables." dhcpcd supports these requests through the "-s" command line option, but the /etc/sysconfig/network-scripts/ifup script doesn't make use of the option. Adding support to ifup is easy enough, as the attached patch shows. It only supports dhcpcd because (AFAIK), pump can't do DHCPINFORM requests.
Created attachment 42352 [details] Add DHCPINFORM support to the ifup initscript
Closing bugs on older, no longer supported, releases. Apologies for any lack of response. Since we don't use dhcpcd any more, closing this.