On Sat, Feb 28, 2015 at 10:23:43PM +0100, Florian Weimer wrote:
> * John Arnold:
>
> > Is configuring Ethernet interfaces with /31 via zebra bugged?
> > Broadcast address gets configured as 0.0.0.0 and pings to the far
> > side don't work. I've reviewed RFC3021 and I think the broadcast
> > address is supposed to be set to link local broadcast,
> > 255.255.255.255.
Real question is: why do pings not work?
> Is the broadcast address actually used by anything?
Indeed - inside Quagga, the only user of the broadcast address is ripd
in non-multicast (RIPv1) mode, but it ignores the one configured in
kernel and derives it from the subnet mask.
(RIPv1 / RIP with directed broadcast is a relic from the 90ies. Any
normal RIP setup uses RIPv2 and multicast.)
> The 50.255.255.255 case is problematic (because it blocks access to
> the IP address), but is the 0.0.0.0 vs 255.255.255.255 choice
> relevant?
When I try to configure a /31 from zebra, I get this:
2: dummy0: <BROADCAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN
group default
link/ether 76:22:8b:fc:01:5c brd ff:ff:ff:ff:ff:ff
inet 192.168.1.55/31 scope global dummy0
valid_lft forever preferred_lft forever
which looks correct to me. (Note there is no broadcast address
displayed; iproute2 would show that as "brd 1.2.3.4". This is indeed
the same as trying to configure "0.0.0.0" as broadcast address, so I
guess this is a UI/semantics problem?)
I've personally not seen 255.255.255.255 show up as broadcast address in
iproute2 output (= I'm not a Debian user). My understanding is that the
field in the kernel is for directed broadcast (since undirected /
255.255.255.255 works anyway, independently); for /31s there simply is
no subnet broadcast address hence 0.0.0.0 or "nonoe" is OK.
-David
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