I have two interfaces eth0 and eth1 as follow.

eth0
IP: 10.0.0.50
Mask: 255.0.0.0

eth1
IP: :216.236.98.37
Mask: 255.255.255.240
GW: 216.236.98.33

I want to use eth1 as my external interface (for internet) and 216.236.98.33 as gateway and it was working perfect but now my internet performance goes down very badly. I am feeling that my routing table causing problem.

Here is my routing table output.

Destination Gateway Genmask Flags Metric Ref Use Iface
216.236.98.32 * 255.255.255.240 U 0 0 0 eth1
10.0.0.0 * 255.0.0.0 U 0 0 0 eth0
127.0.0.0 * 255.0.0.0 U 0 0 0 lo
default 216.236.98.33 0.0.0.0 UG 0 0 0 eth1

Is it correct or I have to make some changes and I want to know is there any impact of NATing and MASQEURADing on routing table. If yes then here is my iptables rules list.

touch /var/lock/subsys/local
echo "1" > /proc/sys/net/ipv4/ip_forward
iptables -F -t mangle
iptables -Z -t mangle
iptables -F -t nat
iptables -Z -t nat
iptables -F
iptables -Z
iptables -t nat -A POSTROUTING -o eth1 -j MASQUERADE
iptables -t nat -A PREROUTING -p tcp --dport 80 -j REDIRECT --to-port 8080
iptables -t mangle -A FORWARD -p tcp --dport 1863 -j TOS --set-tos Minimize-Delay
iptables -t mangle -A FORWARD -p tcp --dport 5000 -j TOS --set-tos Minimize-Delay
iptables -t mangle -A FORWARD -p tcp --dport 5050 -j TOS --set-tos Minimize-Delay

Please help me this problem making me mad.