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I have a dual-homed device running Debian acting as my home router, and I'm following these instructions to get fq_codel usefully working with my VDSL connection. I know the instructions refer to Gentoo but the principles are the same.

I have these interfaces:

  • eth0: external interface connected to VDSL modem
  • ppp0: decapsulated traffic from pppd
  • eth1: internal interface

My question refers to this line in the linked script:

$tc qdisc add dev $ext handle ffff: ingress

Should I use eth0 or ppp0 as the value of $ext when creating the ingress IFB?

Flup
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1 Answers1

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Almost certainly ppp0, since that's the thing you want to shape.

eth0, if directed to a DSL modem (not router) directly, will either remain unused (merely a transport for ppp0), or it could also be a configuration channel to the modem itself.

Some modems have interfaces to query DSL signal quality and other such data. But that's local networking/monitoring, not internet traffic, so it should not be included in the shaping efforts.

It might be different if eth0 was connected to a switch, and a DSL router just one of many devices used on that line, but then you would most likely not see a ppp0 device on the box (that's on the router directly then) and the question would not come up...

If eth0 is connected to an antique hub so you have ppp0 and also other devices using eth0 for regular networking ... there is no way to shape that.

frostschutz
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  • Makes a lot of sense, thanks! My eth0 is connected directly to the modem so I guess ppp0 is the way to go. – Flup Feb 20 '18 at 21:12