in your test lab, you can always change eth6/7 to eth4/5 eth3/4 (assuming you're not using all 8 ports of the ER-8, of course).
edit -- oops, eth4/5 would be for the ER-X-SFP
in your test lab, you can always change eth6/7 to eth4/5 eth3/4 (assuming you're not using all 8 ports of the ER-8, of course).
edit -- oops, eth4/5 would be for the ER-X-SFP