Bug 549892

Summary:	glibc default address selection policy should prefer ipv4 addresses
Product:	[Fedora] Fedora	Reporter:	Jason Merrill <jason>
Component:	glibc	Assignee:	Andreas Schwab <schwab>
Status:	CLOSED NOTABUG	QA Contact:	Fedora Extras Quality Assurance <extras-qa>
Severity:	medium	Docs Contact:
Priority:	medium
Version:	11	CC:	drepper, jakub, kdudka, schwab
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Hardware:	All
OS:	Linux
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Fixed In Version:		Doc Type:	Bug Fix
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Last Closed:	2010-01-25 17:18:00 UTC	Type:	---
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Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
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Embargoed:

Description Jason Merrill 2009-12-22 22:25:25 UTC

Description of problem:

Currently, when a hostname resolves to both ipv4 and ipv6 addresses, curl and firefox try the ipv6 address first.  With current network hardware, this is less likely to work; until ipv6 functionality is more universal, the ipv4 address should be preferred.  Many consumer-level routers (such as the two I have) seem to just drop ipv6 packets on the floor.

RFC 3484 talks about configuring this preference in section 10.3.  I could override it myself via gai.conf, but I doubt I am the only one for whom this is an issue.

Version-Release number of selected component (if applicable):

glibc-2.10.2-1.i686

How reproducible:

Always

Steps to Reproduce:
1. curl -v fedoraproject.org
  
Actual results:

* About to connect() to fedoraproject.org port 80 (#0)
*   Trying 2610:28:200:1::fed0:1... Timeout [after 1 minute wait]
*   Trying 66.35.62.162... connected

Expected results:

* About to connect() to fedoraproject.org port 80 (#0)
*   Trying 66.35.62.162... connected

Additional info:

curl-7.19.7-3.fc11.i586

Comment 1 Jason Merrill 2009-12-22 22:53:29 UTC

Hmm, the gai.conf precedence lines from the man page adjusted as suggested in 10.3 of the RFC don't produce the desired result for me:

       precedence  ::1/128       50
       precedence  ::/0          40
       precedence  2002::/16     30
       precedence ::/96          20
       precedence ::ffff:0:0/96  100

and curl/firefox are still trying the ipv6 address first, even after a reboot.

There's also a typo ("precendence") in those lines in the man page, but I get the same behavior with either spelling (or with no gai.conf).

Comment 2 Andreas Schwab 2010-01-04 14:17:54 UTC

What do you get from getent ahosts fedoraproject.org?

Comment 3 Jason Merrill 2010-01-05 02:33:22 UTC

2610:28:200:1::fed0:1 STREAM fedoraproject.org
2610:28:200:1::fed0:1 DGRAM  
2610:28:200:1::fed0:1 RAW    
66.35.62.162    STREAM 
66.35.62.162    DGRAM  
66.35.62.162    RAW    
80.239.156.214  STREAM 
80.239.156.214  DGRAM  
80.239.156.214  RAW    
152.46.7.221    STREAM 
152.46.7.221    DGRAM  
152.46.7.221    RAW

Comment 4 Andreas Schwab 2010-01-05 10:23:14 UTC

You need to fix your network configuration, glibc is following RFC 3484.

Comment 5 Jason Merrill 2010-01-05 13:51:53 UTC

Regardless of the default, surely gai.conf should work as documented?

From /usr/share/doc/glibc-common*/gai.conf:

#    For sites which prefer IPv4 connections change the last line to
#
precedence ::ffff:0:0/96  100

...but this doesn't work.

Comment 6 Andreas Schwab 2010-01-25 17:18:00 UTC

If you are behind a NAT you need to adjust the scope table so that your interface address is no longer classified as link-local.  Otherwise a global scope address will never match.

Comment 7 Jason Merrill 2010-01-26 21:02:46 UTC

I have no idea how to do that, and it seems rather unfortunate to require users in an extremely common situation (i.e. behind a consumer-level NAT router) to jump through so many hoops to get basic functionality to work properly.