Re: AT&T MPLS / BIB Routers

[Jim Gettys <jg () freedesktop org>]

On 02/17/2011 01:02 AM, George Bonser wrote:
> > From: Mikeal Clark
> > Sent: Wednesday, February 16, 2011 3:16 PM
> > To: Jim Gettys
> > Cc: nanog () nanog org
> > Subject: Re: AT&T MPLS / BIB Routers
> >
> > I'm building up to 3000-4000ms latency with these BIB routers.  We
> > never had
> > this issue on the old point to points using Cisco gear.
>
> Something I might try, assuming that the BIB unit plugs into a switch
> port, is to try bandwidth limiting that port to whatever the CIR is of
> the MPLS link.  If buffering in that path is the problem, limiting the
> input bandwidth to the box to the maximum of the output bandwidth should
> eliminate any buffering in the path or the BIB box.  Assuming your old
> Cisco gear was using the same network infrastructure, that might rule
> out excessive buffering in the MPLS path as the cause, unless AT&T can't
> actually deliver the advertized bandwidth across the path they are
> selling.
>
> What is the CIR?  If you have a 10Meg path and have a GigE jacked into
> the box, yeah, it's going to get into buffers pretty quick.  Maybe even
> taking the ethernet port down to 10Meg might help, depending on what you
> are expecting the bandwidth of the path to be.

Yes, bandwidth limiting is something to try.  It's how you can deal with 
your home broadband connection to inject sanity.

Note that you can have bufferbloat just upstream as well.

For example, if you plug a GigE ethernet into a 100Mbps switch, if there 
is buffering upstream, it will fill.

http://gettys.wordpress.com/2010/11/29/home-router-puzzle-piece-one-fun-with-your-switch/

In the test case in that post, the bloating is in the laptop plugged 
into the 100Mbps switch (in the device driver ring, and possibly 
transmit queue).
                        - Jim