Red Hat Bugzilla – Bug 144701
RHEL v3 specific network connection problems over IPv6 across Cisco vlans
Last modified: 2007-11-30 17:07:05 EST
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Description of problem:
I am experiencing problems connecting from RHEL v3 to any other RHEL
v3 machine over IPv6 when the machines in question are on different
vlans. The vlans in question are on the same physical Cisco switch
(don't know if that matters) and the network is currently configured
for IPv4/IPv6 dual-stack. I have experienced this problem when trying
to use several different applications (our own version of ssh and
ktelnet/krcp, etc), but for the sake of this bug I will just discuss
telnet, since it is included with RHEL v3.
Specifically, the problem is that I can telnet from a RHEL v3 machine
to another RHEL v3 machine without any problems over IPv4. If I try
to telnet from a RHEL v3 machine to another RHEL v3 machine over IPv6
the client "hangs" after I have authenticated (i.e. I never get a
IPv6 connections work fine when the two RHEL machines are on the same
vlan. Also, ping6, traceroute6, and DNS requests over IPv6 seem to
all work fine regardless of what vlans the machines are on. I can
telnet over IPv6 between Linux and Solaris machines, that is, the
problem only exists when going from a RHEL machine to another RHEL
Version-Release number of selected component (if applicable):
Steps to Reproduce:
1. Put two RHEL machines on different vlans on a Cisco switch.
2. Make sure each machine gets an IPv6 address
3. Telnet from one machine to the IPv6 address of the other machine
(you can also use the hostname if that hostname has properly
configured AAAA records)
4. Enter your username and then your password
Actual Results: You are properly authenticated and the client sees
the "last connected..." message. Then instead of getting a shell
prompt the client just sits there until you terminate the process.
Expected Results: After authenticating you should get a shell.
Anyone had a chance to look at this yet?
UPDATE: After doing further testing...I have found more specific
information about the problem. The problem only happens when machines
with MTU's set to 1500 are on vlans that have a maximum MTU size of
9180 (i.e. jumbo frame support). If the maximum MTU size of the vlan
is bumped down to 1500 the problem goes away.
Now the question is: Is this a redhat-specific bug, a linux-specific
bug, a cisco-specific bug, or an inherent "feature" of IPv6 itself?
Has anyone at redhat even looked at this yet??????
This bug is filed against RHEL 3, which is in maintenance phase.
During the maintenance phase, only security errata and select mission
critical bug fixes will be released for enterprise products. Since
this bug does not meet that criteria, it is now being closed.
For more information of the RHEL errata support policy, please visit:
If you feel this bug is indeed mission critical, please contact your
support representative. You may be asked to provide detailed
information on how this bug is affecting you.