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Asked: 2026-06-01T21:34:45+00:00

I’m trying to make a custom SIP software work on an EC2 instance. My

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I’m trying to make a custom SIP software work on an EC2 instance. My software at the moment doesn’t have NAT handling capabilities, and I was wondering If I could get it to work transparently with the public (elastic) IP associated to the EC2 instance.

Here’s the output of “iconfig -a” run on my EC2 box:

eth0 Link encap:Ethernet HWaddr XXXXXX
inet addr: PRIVATE-IP-ADDRESS Bcast:10.48.195.255 Mask:255.255.254.0
inet6 addr: XXXXXX/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:3825 errors:0 dropped:0 overruns:0 frame:0
TX packets:3596 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:259666 (253.5 KiB) TX bytes:1106872 (1.0 MiB)

lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:78 errors:0 dropped:0 overruns:0 frame:0
TX packets:78 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:6892 (6.7 KiB) TX bytes:6892 (6.7 KiB)

Is there a way to change this so that my application can transparently open a UDP socket on the PUBLIC (elastic) IP address? And basically work as if the public IP was normally assigned to eth0.

I thought about using iptables DNAT/SNAT or adding the IP address manually, but no success so far.

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1 Answer

  1. Editorial Team

    Answer from https://forums.aws.amazon.com/

    The Elastic IP address is mapped to the instance using 1:1 NAT. The instance itself is not aware of the public address. As this address can’t be bound to the interface, I’m afraid you will need to handle it in another way. You will want to avoid changing the network configuration as it might result in loss of connectivity.

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