[mythtv-users] HDHomeRun tuners and network switches

[Jim Abernathy]

On 1/21/22 5:11 AM, Stephen Worthington wrote:
> On Thu, 20 Jan 2022 10:59:55 -0500, you wrote:
>
>> Thanks for all the suggestions.  I used the hdhomerun_config to capture
>> some video with no errors of any kind now that I kept the tuners from
>> routing through the AP/router.  I think I'm going to move everything out of
>> the AP/router except the one cable to the first switch.
>>
>> JIm A
> I do not know about the AX50, so I do not know how its Ethernet LAN
> ports work.  There are basically two different ways that routers
> handle LAN ports.  One way has the LAN ports connected to the router
> hardware individually and all traffic between the LAN ports goes via
> the routing hardware or the router CPU (or both).  This setup is very
> useful if you want separate LANs with separate routing for each LAN,
> but very bad if you want two or more of the LAN ports to be on the
> same subnet (ie bridged together).
>
> Routers are very bad at bridging - that is a function best left to
> switches.  So packets supposedly on the same subnet that have to
> traverse the router to get to a different LAN port will often have low
> throughput, as the CPU needs to examine and route each packet, and
> router CPUs are not normally very fast.  Routers do high speed routing
> on their dedicated router hardware, and packets that need to be
> examined by the CPU will have low throughput.  Low throughput = low
> bandwidth.  Low bandwidth compared to the 1 gigabit/s of the LAN port
> means that if there is too much traffic, packets will be dropped to
> reduce the traffic down to the amount that can actually be routed
> between the LAN ports.  This is a likely scenario for your setup - UDP
> packets traversing the router between LAN ports are too much for the
> router CPU to handle and are not being routed by the dedicated
> hardware as router hardware usually does not do bridging.  So some UDP
> packets get dropped.  CPU routed packets on my old ERLite router had
> only about 150-200 Mbit/s bandwidth available once I had all my
> firewall rules installed.  Packets routed on its dedicated routing
> hardware had 1 gigabit/s bandwidth.
>
> The plus side of this LAN port configuration is that if you really are
> routing between the LAN ports rather than bridging (ie each LAN port
> has a different subnet on it), then you can get full gigabit routing
> between all the ports (including the CPU/router hardware port and
> access via that to the WAN port).  That assumes that you only use the
> routing features that are handled on the dedicated routing hardware.
> QoS, for example, will usually require the packets to be routed via
> the CPU.
>
> The other way of organising router LAN ports has all the LAN ports on
> a separate internal hardware switch, and also on that switch is an
> internal Ethernet port to the router hardware and/or the router CPU.
> Sometimes there is a separate port for the CPU and the dedicated
> router hardware.  This separate switch works exactly the same as a
> normal external Ethernet switch.  It is usually moderately intelligent
> - it has VLAN capabilities.  You can configure the switch VLANs so
> some of the LAN ports just connect to each other over a VLAN
> (bridged), or there can be a VLAN that connects them to the Ethernet
> port to the router, or some combination of VLANs.  With this sort of
> LAN port configuration, if you have several of your LAN ports on the
> same subnet, you can just configure them to be bridged on the same
> VLAN and there will not be any bandwidth problems with the bridged
> packets.  The bridged packets are handled entirely in the switch
> hardware and are never seen by the CPU or router hardware.  The
> downside of this sort of LAN port configuration is that there is
> contention between the LAN ports for the CPU/router hardware port when
> packets between the LAN ports actually need to be routed instead of
> bridged.  You potentially have say 4 LAN ports wanting all their
> traffic to be routed via one single gigabit port to the CPU/router
> hardware.  In some routers using switched LAN ports, the WAN port can
> also be on the switch, causing contention between WAN packets and LAN
> packets for access to the CPU.
>
> Really good routers that use switched LAN ports solve the problem by
> having a higher speed on the CPU/router hardware port, so if there are
> 4 x 1 gigabit/s LAN ports, the CPU/router hardware port will be 4
> gigabits/s.  Such routers are usually far beyond the means of home
> users to ever contemplate buying.
>
> So what I recommend to people buying a router is to find out which
> sort of router it is and whether that is actually the sort they want,
> depending on what they want their LAN ports to be used for.  I have
> Ubiquity ER4 router, which has separate LAN ports.  In the Ubiquiti
> routers, there are others (such as the ER-X) which have switched LAN
> ports, and some that have a mixture (such as one separate LAN port and
> 5 switched LAN ports).  If you have a small network where you do not
> need any more LAN ports than are switched LAN ports on the router,
> then getting a router with switched LAN ports saves the need to buy a
> separate switch.  But if your needs are larger than that, I think it
> is best to get a router with non-switched LAN ports and also get
> yourself a decent switch or two to go with it.  Do all the routing on
> the router and all the bridging on the switches.  I have a Ubiquiti
> ES-24 Lite switch to go with my ER-4.  It is a full commercial grade
> switch with all the features I might ever need in a switch, except for
> POE.  I also have a simple unmanaged 5 port switch to use whenever I
> have only one Ethernet connection at a location and need more - I can
> use it until I get a new cable installed to that location from my
> ES-24 main switch.
> _____


I appreciate the detailed explanation.  At present all my ports on my 
home network are connected via switches and only one port on the router 
has the top switch in the tree connected to it. So the problem should be 
solved and certainly seems to.

I am curious about the mention of dropped UDP packets being the 
problem.  I thought MythTV v30 and beyond used the TCP method of dealing 
with HDHR tuners so you could get the virtual channels, etc. Maybe I 
don't understand that part of it.

Jim A