Hi All,

We Have a Linux machine with the below kernel Version installed on it. we are seeing an issue with this version, Can anyone help us with this.

[root@ipconn31 ~]# uname -a
Linux ipconn31.mh.lucent.com 2.6.18-308.1.1.el5PAE #1 SMP Wed Mar 7 04:57:46 EST 2012 i686 i686 i386 GNU/Linux

We have IPSec Tunnel up between this linux machine and our Software and have an udpserver listening on the particular IPv6 address and port on the above linux machine which simply loops back the packet received on the IPv6 address and port.

From the Software we are sending an UDP packet whose size is more then the 1500, So the packets get fragmented and lands on the IPv6 address and Port of above linux machine. When the Encapsulated packet is going out of the linux box i see that the next header in the IPv6 header is set to ESP (IPsec protocol) instead of the Fragment Header.

We tried the same scenario with the old kernel Version and i see that the packet going out of the linux box as the next header in the IPv6 header set to Fragment Header and the next header in the Fragment header set to ESP.

Below is the version of the Linux machine, where we see the next header set to Fragment Header in the IPv6 Header.

[root@ipconn30 etc]# uname -a
Linux ipconn30.mh.lucent.com 2.6.18-194.32.1.el5PAE #1 SMP Wed Jan 5 18:43:13 EST 2011 i686 i686 i386 GNU/Linux

Please let us know if any one as faced this issue.

Thanks in advance.

Regards,
Sharad

Unlike in IPv4, routers never fragment a packet. Hosts are expected to use Path MTU Discovery to make their packets small enough to reach the destination without needing to be fragmented.