Maintaining source IP while forwarding port from one host to another, but there is a small issue
I am using this tunnel approach:
https://superuser.com/a/1357450/972858
to forward a port N from x.x.x.x to y.y.y.y. Its working perfectly and destination y.y.y.y is able to see the actual source IP address. But there is one small issue. x.x.x.x:N can be accessed from everywhere but not from y.y.y.y itself. I am not sure why but I unable to telnet x.x.x.x:N from y.y.y.y.
Please help.
linux networking routing port-forwarding iptables
asked Dec 14 at 6:49
Sam
81
add a comment |
I am using this tunnel approach:
https://superuser.com/a/1357450/972858
to forward a port N from x.x.x.x to y.y.y.y. Its working perfectly and destination y.y.y.y is able to see the actual source IP address. But there is one small issue. x.x.x.x:N can be accessed from everywhere but not from y.y.y.y itself. I am not sure why but I unable to telnet x.x.x.x:N from y.y.y.y.
Please help.
linux networking routing port-forwarding iptables
asked Dec 14 at 6:49
Sam
81
Probably the same issue as mentioned: hairpin NAT is necessary.
– grawity
Dec 14 at 7:01
Thanks @grawity for your quick response and your solution to the mentioned question. As I stated, it works beautifully from everywhere except y.y.y.y (destination) cannot telnet the forwarded port N on x.x.x.x. Everywhere -> x.x.x.x:N -> y.y.y.y is working is y.y.y.y is able to see the actual source IP. But if the connection is initiated from y.y.y.y itself: y.y.y.y -> x.x.x.x:N is unable to connect. That is the only issue. Is there a workaround for it? Thanks.
– Sam
Dec 14 at 7:15
add a comment |
I am using this tunnel approach:
https://superuser.com/a/1357450/972858
to forward a port N from x.x.x.x to y.y.y.y. Its working perfectly and destination y.y.y.y is able to see the actual source IP address. But there is one small issue. x.x.x.x:N can be accessed from everywhere but not from y.y.y.y itself. I am not sure why but I unable to telnet x.x.x.x:N from y.y.y.y.
Please help.
linux networking routing port-forwarding iptables
asked Dec 14 at 6:49
Sam
81
I am using this tunnel approach:
https://superuser.com/a/1357450/972858
to forward a port N from x.x.x.x to y.y.y.y. Its working perfectly and destination y.y.y.y is able to see the actual source IP address. But there is one small issue. x.x.x.x:N can be accessed from everywhere but not from y.y.y.y itself. I am not sure why but I unable to telnet x.x.x.x:N from y.y.y.y.
Please help.
linux networking routing port-forwarding iptables
linux networking routing port-forwarding iptables
asked Dec 14 at 6:49
Sam
81
asked Dec 14 at 6:49
Sam
81
asked Dec 14 at 6:49
Sam
81
asked Dec 14 at 6:49
Sam
81
asked Dec 14 at 6:49
Sam
81
81
Probably the same issue as mentioned: hairpin NAT is necessary.
– grawity
Dec 14 at 7:01
Thanks @grawity for your quick response and your solution to the mentioned question. As I stated, it works beautifully from everywhere except y.y.y.y (destination) cannot telnet the forwarded port N on x.x.x.x. Everywhere -> x.x.x.x:N -> y.y.y.y is working is y.y.y.y is able to see the actual source IP. But if the connection is initiated from y.y.y.y itself: y.y.y.y -> x.x.x.x:N is unable to connect. That is the only issue. Is there a workaround for it? Thanks.
– Sam
Dec 14 at 7:15
add a comment |
Probably the same issue as mentioned: hairpin NAT is necessary.
– grawity
Dec 14 at 7:01
Thanks @grawity for your quick response and your solution to the mentioned question. As I stated, it works beautifully from everywhere except y.y.y.y (destination) cannot telnet the forwarded port N on x.x.x.x. Everywhere -> x.x.x.x:N -> y.y.y.y is working is y.y.y.y is able to see the actual source IP. But if the connection is initiated from y.y.y.y itself: y.y.y.y -> x.x.x.x:N is unable to connect. That is the only issue. Is there a workaround for it? Thanks.
– Sam
Dec 14 at 7:15
Probably the same issue as mentioned: hairpin NAT is necessary.
– grawity
Dec 14 at 7:01
Probably the same issue as mentioned: hairpin NAT is necessary.
– grawity
Dec 14 at 7:01
Thanks @grawity for your quick response and your solution to the mentioned question. As I stated, it works beautifully from everywhere except y.y.y.y (destination) cannot telnet the forwarded port N on x.x.x.x. Everywhere -> x.x.x.x:N -> y.y.y.y is working is y.y.y.y is able to see the actual source IP. But if the connection is initiated from y.y.y.y itself: y.y.y.y -> x.x.x.x:N is unable to connect. That is the only issue. Is there a workaround for it? Thanks.
– Sam
Dec 14 at 7:15
Thanks @grawity for your quick response and your solution to the mentioned question. As I stated, it works beautifully from everywhere except y.y.y.y (destination) cannot telnet the forwarded port N on x.x.x.x. Everywhere -> x.x.x.x:N -> y.y.y.y is working is y.y.y.y is able to see the actual source IP. But if the connection is initiated from y.y.y.y itself: y.y.y.y -> x.x.x.x:N is unable to connect. That is the only issue. Is there a workaround for it? Thanks.
– Sam
Dec 14 at 7:15
add a comment |
1 Answer
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This doesn't work for the exactly same reason as why port-forwarding within the same LAN doesn't generally work. In other words, it's a hairpin-NAT situation. (Imagine the tunnel as if it were simply a local LAN network.)
The tunnel itself may be working fine – the packet reaches X, gets NATed, and arrives back at Y. However, because Y sees the original sender as being local, the response does not go through X and therefore X cannot undo the NAT. As a result, addresses in the response do not match addresses in the original packet, and Y (as the original initiator) cannot find a matching connection for the response it just received.
Try adding a -t nat -I PREROUTING -d x.x.x.x --dport N -j REDIRECT rule to iptables to handle this case – it should catch the outgoing packets without having to involve X at all.
answered Dec 14 at 7:31
grawity
232k35490546
Thanks @grawity I added the following on y.y.y.y: iptables -t nat -A PREROUTING -d x.x.x.x -p tcp --dport 80 -j REDIRECT But no go.
– Sam
Dec 14 at 7:40
1
iptables -t nat -A OUTPUT -d x.x.x.x -p tcp --dport N -j REDIRECT works but should I be using that instead of PREROUTING ?
– Sam
Dec 14 at 7:50
1
Ah, yes, for connections initiated by the same system, OUTPUT should be the correct one.
– grawity
Dec 14 at 8:02
add a comment |
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1 Answer
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active
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1 Answer
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active
oldest
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oldest
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active
oldest
votes
This doesn't work for the exactly same reason as why port-forwarding within the same LAN doesn't generally work. In other words, it's a hairpin-NAT situation. (Imagine the tunnel as if it were simply a local LAN network.)
The tunnel itself may be working fine – the packet reaches X, gets NATed, and arrives back at Y. However, because Y sees the original sender as being local, the response does not go through X and therefore X cannot undo the NAT. As a result, addresses in the response do not match addresses in the original packet, and Y (as the original initiator) cannot find a matching connection for the response it just received.
Try adding a -t nat -I PREROUTING -d x.x.x.x --dport N -j REDIRECT rule to iptables to handle this case – it should catch the outgoing packets without having to involve X at all.
answered Dec 14 at 7:31
grawity
232k35490546
Thanks @grawity I added the following on y.y.y.y: iptables -t nat -A PREROUTING -d x.x.x.x -p tcp --dport 80 -j REDIRECT But no go.
– Sam
Dec 14 at 7:40
1
iptables -t nat -A OUTPUT -d x.x.x.x -p tcp --dport N -j REDIRECT works but should I be using that instead of PREROUTING ?
– Sam
Dec 14 at 7:50
1
Ah, yes, for connections initiated by the same system, OUTPUT should be the correct one.
– grawity
Dec 14 at 8:02
add a comment |
This doesn't work for the exactly same reason as why port-forwarding within the same LAN doesn't generally work. In other words, it's a hairpin-NAT situation. (Imagine the tunnel as if it were simply a local LAN network.)
The tunnel itself may be working fine – the packet reaches X, gets NATed, and arrives back at Y. However, because Y sees the original sender as being local, the response does not go through X and therefore X cannot undo the NAT. As a result, addresses in the response do not match addresses in the original packet, and Y (as the original initiator) cannot find a matching connection for the response it just received.
Try adding a -t nat -I PREROUTING -d x.x.x.x --dport N -j REDIRECT rule to iptables to handle this case – it should catch the outgoing packets without having to involve X at all.
answered Dec 14 at 7:31
grawity
232k35490546
Thanks @grawity I added the following on y.y.y.y: iptables -t nat -A PREROUTING -d x.x.x.x -p tcp --dport 80 -j REDIRECT But no go.
– Sam
Dec 14 at 7:40
1
iptables -t nat -A OUTPUT -d x.x.x.x -p tcp --dport N -j REDIRECT works but should I be using that instead of PREROUTING ?
– Sam
Dec 14 at 7:50
1
Ah, yes, for connections initiated by the same system, OUTPUT should be the correct one.
– grawity
Dec 14 at 8:02
add a comment |
This doesn't work for the exactly same reason as why port-forwarding within the same LAN doesn't generally work. In other words, it's a hairpin-NAT situation. (Imagine the tunnel as if it were simply a local LAN network.)
The tunnel itself may be working fine – the packet reaches X, gets NATed, and arrives back at Y. However, because Y sees the original sender as being local, the response does not go through X and therefore X cannot undo the NAT. As a result, addresses in the response do not match addresses in the original packet, and Y (as the original initiator) cannot find a matching connection for the response it just received.
Try adding a -t nat -I PREROUTING -d x.x.x.x --dport N -j REDIRECT rule to iptables to handle this case – it should catch the outgoing packets without having to involve X at all.
answered Dec 14 at 7:31
grawity
232k35490546
This doesn't work for the exactly same reason as why port-forwarding within the same LAN doesn't generally work. In other words, it's a hairpin-NAT situation. (Imagine the tunnel as if it were simply a local LAN network.)
The tunnel itself may be working fine – the packet reaches X, gets NATed, and arrives back at Y. However, because Y sees the original sender as being local, the response does not go through X and therefore X cannot undo the NAT. As a result, addresses in the response do not match addresses in the original packet, and Y (as the original initiator) cannot find a matching connection for the response it just received.
Try adding a -t nat -I PREROUTING -d x.x.x.x --dport N -j REDIRECT rule to iptables to handle this case – it should catch the outgoing packets without having to involve X at all.
answered Dec 14 at 7:31
grawity
232k35490546
answered Dec 14 at 7:31
grawity
232k35490546
answered Dec 14 at 7:31
grawity
232k35490546
answered Dec 14 at 7:31
grawity
232k35490546
232k35490546
Thanks @grawity I added the following on y.y.y.y: iptables -t nat -A PREROUTING -d x.x.x.x -p tcp --dport 80 -j REDIRECT But no go.
– Sam
Dec 14 at 7:40
1
iptables -t nat -A OUTPUT -d x.x.x.x -p tcp --dport N -j REDIRECT works but should I be using that instead of PREROUTING ?
– Sam
Dec 14 at 7:50
1
Ah, yes, for connections initiated by the same system, OUTPUT should be the correct one.
– grawity
Dec 14 at 8:02
add a comment |
Thanks @grawity I added the following on y.y.y.y: iptables -t nat -A PREROUTING -d x.x.x.x -p tcp --dport 80 -j REDIRECT But no go.
– Sam
Dec 14 at 7:40
1
iptables -t nat -A OUTPUT -d x.x.x.x -p tcp --dport N -j REDIRECT works but should I be using that instead of PREROUTING ?
– Sam
Dec 14 at 7:50
1
Ah, yes, for connections initiated by the same system, OUTPUT should be the correct one.
– grawity
Dec 14 at 8:02
Thanks @grawity I added the following on y.y.y.y: iptables -t nat -A PREROUTING -d x.x.x.x -p tcp --dport 80 -j REDIRECT But no go.
– Sam
Dec 14 at 7:40
Thanks @grawity I added the following on y.y.y.y: iptables -t nat -A PREROUTING -d x.x.x.x -p tcp --dport 80 -j REDIRECT But no go.
– Sam
Dec 14 at 7:40
1
1
iptables -t nat -A OUTPUT -d x.x.x.x -p tcp --dport N -j REDIRECT works but should I be using that instead of PREROUTING ?
– Sam
Dec 14 at 7:50
iptables -t nat -A OUTPUT -d x.x.x.x -p tcp --dport N -j REDIRECT works but should I be using that instead of PREROUTING ?
– Sam
Dec 14 at 7:50
1
1
Ah, yes, for connections initiated by the same system, OUTPUT should be the correct one.
– grawity
Dec 14 at 8:02
Ah, yes, for connections initiated by the same system, OUTPUT should be the correct one.
– grawity
Dec 14 at 8:02
add a comment |
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Probably the same issue as mentioned: hairpin NAT is necessary.
– grawity
Dec 14 at 7:01
Thanks @grawity for your quick response and your solution to the mentioned question. As I stated, it works beautifully from everywhere except y.y.y.y (destination) cannot telnet the forwarded port N on x.x.x.x. Everywhere -> x.x.x.x:N -> y.y.y.y is working is y.y.y.y is able to see the actual source IP. But if the connection is initiated from y.y.y.y itself: y.y.y.y -> x.x.x.x:N is unable to connect. That is the only issue. Is there a workaround for it? Thanks.
– Sam
Dec 14 at 7:15