Is the firewall of Phillips CAW7740N router too sensitive?

Question

I got a CAW7740N Router behind a Motorola SBV5121E Modem and from time to time the connection is very slow. Every time I figured out that there are similar entries in the routers security log:

08/12/2011  22:03:44 DHCP Client: [WAN]Receive Ack from xx.xx.xx.xx,Lease time=3600
08/12/2011  22:03:44 DHCP Client: [WAN]Send Request, Request IP=xx.xx.xx.xx

It usually occurs with web-application-like websites like Facebook or Flickr and often if I load more than one page very quickly simultaneously. I think that the slow down doesn't occur if I turn off the routers firewall. Or could the old Motorola Modem be a problem?

Here are the security settings:

Stateful Packet Inspection:

SPI and Anti-DoS firewall protection: on
RIP defect: off
Discard Ping To WAN Interface: on

Stateful Packet Inspection:

Packet Fragmentation: on
TCP Connection: on
UDP Session: on
FTP Service: on
H.323 Service: on
TFTP  Service: on

Connection Policy:
Fragmentation half-open wait: 10sec
TCP SYN wait: 30sec
TCP FIN wait: 5sec
TCP connection idle timeout: 3600sec
UDP session idle timeout: 30sec
H.323 data channel idle timeout: 180sec

DoS Detect Criteria:
Total incomplete TCP/UDP sessions HIGH: 300 session
Total incomplete TCP/UDP sessions LOW: 250 session
Incomplete TCP/UDP sessions (per min) HIGH: 250 session
Incomplete TCP/UDP sessions (per min) LOW: 200 session
Maximum incomplete TCP/UDP sessions number from same host: 50
Incomplete TCP/UDP sessions detect sensitive time period: 500msec
Maximum half-open fragmentation packet number from same host: 150   
Half-open fragmentation detect sensitive time period: 10000msec
Flooding cracker block time: 300sec

Answer 1

It helped to maximize the values to the limits. But now I experience complete freezes from time to time so that I have to reboot the router every other day.

I've found out that this seems to be some kind of monday production. In rare cases Phillips CAW7740N routers are slow, the firewall crashes and it freezes from time to time.

So what do we learn: don't buy Phillips.