# Listen ipv4 to ipv6 backend server

**URL:** <https://discourse.haproxy.org/t/listen-ipv4-to-ipv6-backend-server/9373>\
**Category:** Help!\
**Created:** [January 5, 2024, 12:25pm UTC](https://discourse.haproxy.org/t/listen-ipv4-to-ipv6-backend-server/9373 "2024-01-05T12:25:08Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![benedict6](https://sea2.discourse-cdn.com/flex016/user_avatar/discourse.haproxy.org/benedict6/32/2139_2.png) [@benedict6](https://discourse.haproxy.org/u/benedict6)\
**Post date:** [January 5, 2024, 12:25pm UTC](https://discourse.haproxy.org/t/listen-ipv4-to-ipv6-backend-server/9373/1 "2024-01-05T12:25:08Z")

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Hi, I am using haproxy to send traffic/requests to multiple backend server IPs but my problem is that i  
cant send traffic/requests to an ipv6 backend server. (but ipv4 works fine)

I tried the following as backend servers but they didnt work:

server s1 [ipv6.domain.com:443](http://ipv6.domain.com:443) resolvers mydns resolve-prefer ipv6  
server s1 [ipv6.domain.com:443](http://ipv6.domain.com:443)  
server s1 appIPv6:443  
server s1 appIPv6:::443  
server s1 appIPv6::1:443  
server s1 [appIPv6::1]:443  
server s1 [appIPv6]:443

what is the problem?  
on the backend server i also run haproxy and i done like this:  
…  
listen front  
mode tcp  
bind :::443 v4v6  
…  
use\_backend app …  
backend app  
mode tcp  
server sr1 127.0.0.1:1123

backend server IPv6 is ok and has connection, but does not work in haproxy to send traffic/requests from front end to ipv6 backend server.  
HAProxy version 2.4.22-0ubuntu0.22.04.3 2023/12/04

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<div class="post-metadata">

**Author:** ![AaronWest](https://sea2.discourse-cdn.com/flex016/user_avatar/discourse.haproxy.org/aaronwest/32/164_2.png) [@AaronWest](https://discourse.haproxy.org/u/AaronWest)\
**Post date:** [January 5, 2024, 7:21pm UTC](https://discourse.haproxy.org/t/listen-ipv4-to-ipv6-backend-server/9373/2 "2024-01-05T19:21:59Z")

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It’s probably the backend app… It’s going to see headers with IPv4 addresses which can confuse it…

I assume it works IPv6 to IPv6…?

have a look at the headers, try an experiment like rewriting the headers such as the client ip…

This is the sort of issue I’m referring to: [azure - How to configure IIS 8.5 to accept translated IPv4-\>IPv6 address in host header - Server Fault](https://serverfault.com/questions/807094/how-to-configure-iis-8-5-to-accept-translated-ipv4-ipv6-address-in-host-header)