There is a possibly related bug being discussed on the babel-users list  with an easy fix.

Not sure what kernel versions it happens on.

On Apr 24, 2013 11:39 AM, "Robert Bradley" <robert.bradley1@gmail.com> wrote:
On 20/04/13 10:56, Dave Taht wrote:
iproute2's ip/iproute2.c code has a function called iproute_modify,
which to a blurring eye appears to be capable of doing an atomic route
update via it's netlink interface.

"        if (matches(*argv, "change") == 0 || strcmp(*argv, "chg") == 0)
                 return iproute_modify(RTM_NEWROUTE, NLM_F_REPLACE,
                                       argc-1, argv+1);
         if (matches(*argv, "replace") == 0)
                 return iproute_modify(RTM_NEWROUTE, NLM_F_CREATE|NLM_F_REPLACE,
                                       argc-1, argv+1);"

The babel  native daemon and the quagga-re code, however, does a
delete/add, which results in packets dropping on the floor when a
route changes.


I think quagga-RE would take a lot of work, as you'd need to teach it about modifying routes.  The standalone babeld looks promising though, and I have a basic patch up on GitHub (git://github.com/rb12345/babeld.git).  One issue is that it seems difficult to actually flush the IPv6 route cache, at least on Ubuntu, as writes to /proc/sys/net/ipv6/route/flush appear to be ignored.  The iproute2 approach is to query all cached routes and misuse its internal print_route function to remove each route when flushing the IPv6 cache.

At the moment, the code compiles fine, and I am in the process of testing it here.

--
Robert Bradley

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