How to setup iptables redirect?

Question

System administration

Good evening.
There is server A and server B. You need to configure tcp and udp redirection from A:22513 to B:22513 (well, return of response packets)
I do this

iptables -t nat -A PREROUTING --dst A -p tcp --dport 22513 -j DNAT --to-destination B:22513 
iptables -t nat -A PREROUTING --dst A -p udp --dport 22513 -j DNAT --to-destination B:22513 

iptables -I FORWARD 1 -i eth0 -o eth1 -d A -p tcp -m tcp --dport B -j ACCEPT

iptables -t nat -A POSTROUTING --dst B -p tcp --dport 22513 -j SNAT --to-source A
iptables -t nat -A POSTROUTING --dst B -p udp --dport 22513 -j SNAT --to-source A

Everything is saved, but when testing (via tracetcp), the trace reaches node A (the node itself is not displayed in the trace and goes into endless Request timed out lines)

[~]# iptables -L
Chain INPUT (policy ACCEPT)
target     prot opt source               destination
ACCEPT     udp  --  anywhere             anywhere            udp dpt:22513 state NEW
ACCEPT     tcp  --  anywhere             anywhere            tcp dpt:22513 state NEW

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination
ACCEPT     udp  --  anywhere             B      udp dpt:22513
ACCEPT     tcp  --  anywhere             B      tcp dpt:22513

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination

What am I doing wrong?

Answer 1

The INPUT chain is not traversed by transit packets.
In the FORWARD chain, you still have a policy that allows everything, so there is no point in the rules there. After changing the default policy, do not forget to add reverse rules, with source port 22513. Are there
pings to B?
The port is open, connection with A is possible?
Is the route to B registered?
Does B have incoming blocking? You need to allow access A to port 22513.
Show
cat /proc/sys/net/ipv4/ip_forward
iptables -t nat -S
iptables -S FORWARD
ip route sh