[LARTC] T1 (hardware pre-shaped) shaping question

["Peter Rabbitson" <rabbit@rabbit.us>]

Hello list. I have been trying to figure this out on my own, but I guess I
somewhat failed :) A linux router with external eth0 and internal eth1 acts
as a gateway for a number of machines utilizing a partial T1 line (512kbps).
Since the T1 is limited by hardware and by its nature to 64kbps per channel
the most I can pump out of it is up+down < 512kbps. If a number of
workstations amount to more than this limit the connection starts to choke
e.g. delivers very low performance even on simple http requests.
Right now I have HTBs installed on both eth0 and eth1.
The HTB with subclasses on eth0 governs outgoing traffic (smtp and http).
The HTB on eth1 on the other hand covers all request from the internal
clients (http, streaming audio etc). Everything works well except the fact
that both shaping trees have no idea about each other. Do I have the ability
to tie them together so COMBINED they do not exceed 512k? For example
somebody from the internet is pulling a file by http on eth0 and I am
pumping out smtp, totalling 56k/s. The workstation of my webmaster tries to
download a file through eth1 , and since it has priority the outgoing
traffic on eth0 is cut down to 30k/s and the webmaster gets an incomming
channel through eth0 --> eth1 --> workstation of 32k/s with some leftovers
for TCP checksums. Is this feasible? Or is there another traffic shaping
model different from tc that would treat eth0 as a two way pipe?
Thank you for your replies.

Peter

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