[Cerowrt-devel] mdns reflector issues on ipv6/babel routing through nat.

Jim Gettys jg at freedesktop.org
Sun Mar 18 14:27:30 PDT 2012

Oh, cool.  Broadcast storms are soooo much fun...
                - Jim

On 03/18/2012 05:24 PM, Dave Taht wrote:
> On Sun, Mar 18, 2012 at 2:22 PM, Dave Taht <dave.taht at gmail.com> wrote:
>> Once you get to a few routers, a few deep, (3 in series in this case,
>> 9 overall), the avahi mdns proxy starts to malfunction over ipv6, and
>> I ended up with a rather nasty broadcast storm.
>> So I had to disable the ipv6 multicast of mdns in order to get my
>> network back in this (excessively) complex network.
>> use-ipv6=no in the /etc/avahi/avahi-daemon file
>> Seems to work fine, two deep. Curiously, I did not observe a similar
>> storm for ipv4...
>> Now this is across like 5 different versions of cerowrt, but it would
>> not surprise me that this is a  generic problem with avahi on ipv6,
>> and/or a symptom of the brain-damaged-ness of mdns in the first place.
>> use-ipv6=no
>> I note that when you connect cero boxes together in a babel mesh
>> configuration, site-local multicast is not a problem, because it
>> doesn't work in the first place (by design). This can be construed as
>> an advantage (no broadcast storm), or disadvantage (mdns and
>> site-local multicast doesn't work across meshed links)
> Actually  I was wrong. I'm STILL observing a broadcast storm, AND it
> is taking place across the meshed links too.... aggggh.....
>> Incidentally, I don't know if anyone would purposely inflict a network
>> this complex on themselves:
>> http://pastebin.com/LzeeiCXg
>> but it does illustrate that a complex, automagically routed, fault
>> tolerant ipv4 and ipv6 network IS feasible, so long as all internal
>> addresses are unique.
>> The biggest problem I run into is that 'failover-capable,
>> fault-tolerant routing' introduces major headaches with firewall
>> rules.
>> Another thing the above paste illustrates that you can mix and match
>> ipv4 nat with ipv6 fully meshed routing.
>> The box I took that trace off has babel enabled on all interfaces, and
>> has the following rule at the top of it's babeld.conf file
>> out if ge00 ip deny
>> (as do multiple other boxes in the lab on the external network)
>> this prohibits announcing ipv4 routes across the natted ge00
>> interface, but allows ipv6. In the caseof that paste, this particular
>> router has NO internal wired connections at all, it just meshes
>> internally for ipv4, and because ge00 is a higher quality (ethernet)
>> interface, babel chooses it for the default for ipv6 for most routes.
>> --
>> Dave Täht
>> SKYPE: davetaht
>> US Tel: 1-239-829-5608
>> http://www.bufferbloat.net

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