[bdNOG] Can't access a website using dual stack

Sun Feb 5 19:36:58 BDT 2017

On 05/02/2017 12:49, Md. Abdul Awal wrote:
> Those who are using dual stack, would you please check if you can browse
> Malaysian High Commission's page http://www.kln.gov.my/web/bgd_dhaka/home ?
>
> When I use IPv4 only, it works fine. When I use IPv6 only I can't browse
> the page, but it seems the website is IPv6 enabled.
>
> Surprisingly, if I use dual stack, I can't browse the page which is the
> main problem I'm facing. I can't figure out whether the problem is in my
> network or at their end. I'd really appreciate if somebody help me
> through this?
The problem is with their site.

If it simply failed to connect on IPv6, a dual-stack browser would fall 
back to IPv4.

However, what's actually happening is that it's accepting the connection 
on IPv6, but then hanging and not returning any content. In this 
situation, a dual-stack browser thinks the connection was successful so 
will not fall back.

$ curl -v http://www.kln.gov.my/web/bgd_dhaka/home
* About to connect() to www.kln.gov.my port 80 (#0)
*   Trying 2400:7400:51:7d::20... connected
 > GET /web/bgd_dhaka/home HTTP/1.1
 > User-Agent: curl/7.22.0 (x86_64-pc-linux-gnu) libcurl/7.22.0 
OpenSSL/1.0.1 zlib/1.2.3.4 libidn/1.23 librtmp/2.3
 > Host: www.kln.gov.my
 > Accept: */*
 >
<<< hangs here >>>

Whereas if I force the connection on IPv4, it returns content:

$ curl -4 -v http://www.kln.gov.my/web/bgd_dhaka/home
* About to connect() to www.kln.gov.my port 80 (#0)
*   Trying 202.60.59.122... connected
 > GET /web/bgd_dhaka/home HTTP/1.1
 > User-Agent: curl/7.22.0 (x86_64-pc-linux-gnu) libcurl/7.22.0 
OpenSSL/1.0.1 zlib/1.2.3.4 libidn/1.23 librtmp/2.3
 > Host: www.kln.gov.my
 > Accept: */*
 >
< HTTP/1.1 200 OK
< Set-Cookie: JSESSIONID=202EBBC7FD0F7144C5FA2A78B9DF4A58; Path=/
< Liferay-Portal: Liferay Portal Standard Edition 5.2.3 (Augustine / 
Build 5203 / May 20, 2009)
< Content-Type: text/html;charset=UTF-8
< Content-Length: 110759
< Date: Sun, 05 Feb 2017 13:33:30 GMT
< Server: wisma
<
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" 
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html dir="ltr" xmlns="http://www.w3.org/1999/xhtml">
<head>    <title>Portal - Home</title>
... etc

So you should get in touch with them. Either they should fix the serving 
of content over IPv6, or they should remove the AAAA record from the DNS.

Regards,

Brian.