Bug 477976 - MTU not set correctly for 6to4
MTU not set correctly for 6to4
Product: Fedora
Classification: Fedora
Component: initscripts (Show other bugs)
All Linux
low Severity medium
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Assigned To: Bill Nottingham
Fedora Extras Quality Assurance
Depends On:
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Reported: 2008-12-26 15:44 EST by Allen Kistler
Modified: 2014-03-16 23:16 EDT (History)
2 users (show)

See Also:
Fixed In Version: 8.86.3-1
Doc Type: Bug Fix
Doc Text:
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Clone Of:
Last Closed: 2009-01-05 13:43:45 EST
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RHEL 7.3 requirements from Atomic Host:
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Attachments (Terms of Use)
Patch for /etc/sysconfig/network-scripts/network-functions-ipv6 (478 bytes, patch)
2008-12-26 15:44 EST, Allen Kistler
no flags Details | Diff

  None (edit)
Description Allen Kistler 2008-12-26 15:44:24 EST
Created attachment 327863 [details]
Patch for /etc/sysconfig/network-scripts/network-functions-ipv6

Description of problem:
MTU of a 6to4 tunnel setup by /etc/ppp/ip-up.ipv6to4 has an incorrect value.  The bug was tracked to a file provided by initscripts for IPv6.  (See "Additional info" for discussion.)

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

How reproducible:

Steps to Reproduce:
1. Configure 6to4 to use ppp connection (DSL) from /etc/ppp
2. Run /etc/ppp/ip-up.ipv6to4
3. Observe MTU with "ifconfig tun6to4"

Actual results:
MTU is 1480

Expected results:
MTU should be 1472, which 20 less than the MTU of ppp0

Additional info:
I tracked the bug to /etc/sysconfig/network-scripts/network-functions-ipv6.

The routine ipv6_set_mtu writes the correct value to /proc/sys/net/ipv6/conf/tun6to4/mtu using sysctl, so the MTU is calculated correctly, but set ineffectively.

The corresponding function for IPv4 uses /sbin/ip to set the MTU.

Changing the call to ipv6_exec_sysctl into a call to ipv6_exec_ip (and generally getting rid of all references to /proc in ipv6_set_mtu) produces the expected result and doesn't appear to break anything else, either.

Patch attached.

Although this bug is filed against F9, the same bug probably exists in F10, although I haven't checked.
Comment 1 Allen Kistler 2008-12-30 00:11:11 EST
I verified that the bug does exist in F10, as well.  I opened Bug 478441 with an F10-appropriate patch file attached.
Comment 2 Bill Nottingham 2009-01-05 13:43:45 EST

*** This bug has been marked as a duplicate of bug 478441 ***
Comment 3 Fedora Update System 2009-04-02 14:05:04 EDT
initscripts-8.86.1-1 has been submitted as an update for Fedora 10.
Comment 4 Fedora Update System 2009-04-03 00:16:44 EDT
initscripts-8.86.2-1 has been submitted as an update for Fedora 10.
Comment 5 Fedora Update System 2009-04-22 16:23:14 EDT
initscripts-8.86.3-1 has been pushed to the Fedora 10 stable repository.  If problems still persist, please make note of it in this bug report.

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