[Cake] Cake on elements of a bridge

[Pete Heist]

> On Sep 6, 2018, at 8:51 PM, Pete Heist <pete at heistp.net> wrote:
> 
>> On Sep 6, 2018, at 8:04 PM, Toke Høiland-Jørgensen <toke at toke.dk <mailto:toke at toke.dk>> wrote:
>> 
>> Pete Heist <pete at heistp.net <mailto:pete at heistp.net>> writes:
>> 
>>> But now, my neighbor will access the Internet through my CPE device,
>>> but they must have a separate IP obtained through DHCP (i.e. a
>>> separate MAC address as well), and I want to use cake to manage the
>>> queue for both of us. I could do this with two routers and a
>>> transparent bridge, but I want to see if I can make it work with as
>>> few devices as possible, preferably just one EdgeRouter-X. I had two
>>> failures thus far:
>> 
>> DHCP relay and normal routing? Or bridging with a kernel software bridge
>> rather than the hardware switch?
> 
> I bet a regular software bridge would work. I’ll try it.
> 
> It looks like I’ll also need to do stateful firewalling for the neighbors. I was able to get my transparent bridge to do this with net.bridge.bridge-nf-call-iptables=1, I believe, so this should also theoretically work fine, somehow… :)

For anyone who followed this, yes, the regular soft bridge (i.e. set interfaces bridge br0) works fine on the ER-X, as I suspect it would on most any Linux. A few notes about it:

- Your qdisc must be added to the physical interface (e.g. eth4), not the bridge interface
- Unlike the hardware bridge which has its own MAC, the soft bridge seems to take the MAC of the lowest (or first listed?) interface port
- On ER-X, bridge-nf-call-iptables=1 is the default so nothing needs to be changed there for firewalling
- When firewalling the bridged WAN interface, ‘in’ corresponds to bridged traffic and ‘local’ to routed traffic, which is different from the semantics for ordinary routed traffic
- I can do stateful firewalling for bridged hosts with “accept established and related”, but have to explicitly allow DHCP (UDP source/dest port 67-68) in the WAN interface’s ‘in’ rules for DHCP traffic to pass through the bridge

Performance:

Using Cake with this setup, the fun ends at around 110 Mbit with ksoftirqd thrashing. Unsurprisingly, there’s probably some overhead here with the soft bridge. For my purposes though (50 Mbit), it’s enough, barely…

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