pppoe-server replies never make it to the client

I am using rp-pppoe 3.8 and starting the server like this

pppoe-server -I eth1 -L 10.0.0.1 -R 10.0.0.2

and in /etc/ppp/pppoe-server-options, I set:

lcp-echo-interval 10
lcp-echo-failure 2
require-pap
debug
dump
proxyarp

pppoeconf finds the concentrator and configures the PPPoE
connection, but when I start it, packages from the server to the
client are lost. For instance, in syslog, the client sends a config
request:

sent [LCP ConfReq id=0x1 <magic 0x9cf04f82>]

which the server receives and answers:
...
connect: ppp0 <--> /dev/pts/4
...
rcvd [LCP ConfReq id=0x1 <magic 0x9cf04f82>]
sent [LCP ConfAck id=0x1 <magic 0x9cf04f82>]

However, the client never receives anything. Thus, it eventually
times out:

LCP: timeout sending Config-Requests
Connection terminated.


I already installed a PPTP server on this machine, and my pppd is 2.4.3
in Debian Sarge
Does anyone has the answer for it? Thank you in advance.