[ILUG] Quagga temporarily drops routes after ifup eth0:1

[Kenn Humborg]

Centos5.2.  quagga-0.98.6-5.el5.

I have a host with two NICs, one on the Internet
and one internal.  It runs quagga'a ospfd to 
exchange routing info over the internal NIC to
other internal hosts.

I want to add another IP address to the external NIC.

If I do

   ip addr add xx.xx.xx.xx/xx broadcast xx.xx.xx.xx dev eth0

all the OSPF routes are removed from
the routing table for maybe 20 seconds or more,
seemingly while ospfd re-calculates the routes.

The ospfd config is trivial:

   # cat /etc/quagga/ospfd.conf
   log syslog
   router ospf
     network 10.123.0.0/16 area 0

The zebra config is empty:

   # cat /etc/quagga/zebra.conf
   log syslog

The address I'm adding above is not in the 10.123.0.0/16 
network.

Surely, a routing daemon should be able to handle an 
interface or address that has nothing to do with 10.123.0.0
coming up or going down without killing off all dynamic
routes?

What am I missing?

Later,
Kenn