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):
initscripts-8.76.4-1.i386

How reproducible:
Always

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.