TCP uses wrong MTU/MSS size for IPv6
Affects | Status | Importance | Assigned to | Milestone | |
---|---|---|---|---|---|
linux (Ubuntu) |
Expired
|
Medium
|
Unassigned | ||
Bug Description
TCP uses an MSS of 1440 although the IPv6 MTU size is set to 1280 by auto configuration (router advertisements). This worked well under gutsy so far, but now TCP connections fail because PMTU discovery does not work from the other end correctly (probably due to tunnel ingress).
TCP must not use a value larger than the MTU
During SYN-Handshake my hardy system sends:
Transmission Control Protocol, Src Port: 47070 (47070), Dst Port: http (80), Seq: 0, Len: 0
Source port: 47070 (47070)
Destination port: http (80)
Sequence number: 0 (relative sequence number)
Header length: 40 bytes
Flags: 0x02 (SYN)
Window size: 5760
Checksum: 0xc4b5 [correct]
Options: (20 bytes)
Maximum segment size: 1440 bytes
SACK permitted
Timestamps: TSval 58913848, TSecr 0
NOP
Window scale: 7 (multiply by 128)
Although:
net.ipv6.
ip -6 r s default
default via fe80::207:
advmss is obviously wrong
Changed in linux: | |
status: | Incomplete → New |
Changed in linux: | |
assignee: | nobody → ubuntu-kernel-team |
importance: | Undecided → Medium |
status: | New → Triaged |
Changed in linux: | |
assignee: | nobody → ipv6 |
assignee: | ipv6 → nobody |
tags: | added: ipv6 |
The Ubuntu Kernel Team is planning to move to the 2.6.27 kernel for the upcoming Intrepid Ibex 8.10 release. As a result, the kernel team would appreciate it if you could please test this newer 2.6.27 Ubuntu kernel. There are one of two ways you should be able to test:
1) If you are comfortable installing packages on your own, the linux-image- 2.6.27- * package is currently available for you to install and test.
--or--
2) The upcoming Alpha5 for Intrepid Ibex 8.10 will contain this newer 2.6.27 Ubuntu kernel. Alpha5 is set to be released Thursday Sept 4. Please watch http:// www.ubuntu. com/testing for Alpha5 to be announced. You should then be able to test via a LiveCD.
Please let us know immediately if this newer 2.6.27 kernel resolves the bug reported here or if the issue remains. More importantly, please open a new bug report for each new bug/regression introduced by the 2.6.27 kernel and tag the bug report with 'linux-2.6.27'. Also, please specifically note if the issue does or does not appear in the 2.6.26 kernel. Thanks again, we really appreicate your help and feedback.