A fix is available
APAR status
Closed as unreproducible in next release.
Error description
TCPIP received an IPv6 ICMP message indicating "packet too big". The MTU received in the ICMP message was 1272. EZBTCRDE called EZB6POUT to send the packet with the smaller MTU. Since the packet was less than the minimum IPv6 MTU of 1280, the send got rejected with a EMSGSIZE error and an MTU of 1272. This caused a loop, eventually running out of DSA storage. . VERIFICATION STEPS: 1) 4C5 abend will occur 2) Calling sequence of abend thread will be a loop: INDEX DUAE DUCB DUSA ASCB ASID JOBNAME ABEND STATUS 10000428 42D19568 7F5A9000 7F5A91A0 00F83C00 000F DMP50030 004C5000 Ab Iu Su RSA 7F5A96E8 Prev 424802A0 Next 7F5A97D8 Mod EZBIFRC1 RSA 7F5A97E0 Prev 7F5A96E8 Next 7F5AA790 Mod EZBIFINB RSA 7F5AA798 Prev 7F5A97E0 Next 7F5ABD18 Mod EZBTCRD: RSA 7F5ABD20 Prev 7F5AA798 Next 7F5AC550 Mod EZBTCRDE RSA 7F5AC558 Prev 7F5ABD20 Next 7F5AD720 Mod EZB6POUT RSA 7F5AD728 Prev 7F5AC558 Next 7C4A3038 Mod EZBTCRDE RSA at 7C4A3040 is outside address range of DUSA RSA 7C4A3040 Prev 7F5AD728 Next 7C4A4208 Mod EZB6POUT RSA 7C4A4210 Prev 7C4A3040 Next 7C4A4A40 Mod EZBTCRDE RSA 7C4A4A48 Prev 7C4A4210 Next 7C4A5C10 Mod EZB6POUT RSA 7C4A5C18 Prev 7C4A4A48 Next 7C4A6448 Mod EZBTCRDE RSA 7C4A6450 Prev 7C4A5C18 Next 7C4A7618 Mod EZB6POUT RSA 7C4A7620 Prev 7C4A6450 Next 7C4A7E50 Mod EZBTCRDE RSA 7C4A7E58 Prev 7C4A7620 Next 7C4A9020 Mod EZB6POUT RSA 7C4A9028 Prev 7C4A7E58 Next 7C4A9858 Mod EZBTCRDE RSA 7C4A9860 Prev 7C4A9028 Next 7C4AAA28 Mod EZB6POUT RSA 7C4AAA30 Prev 7C4A9860 Next 7C4AB260 Mod EZBTCRDE 3) Ctrace with option INTERNET will show record GERMANY INTERNET 300101BC 12:03:12.764131 Cant fragment IPv6 outbound packet HASID..0010 PASID..0010 SASID..0010 USER...DMP50030 TCB....00000000 MODID..EZB6POUT REG14..4317F6AC DUCB...4B001422 CID....0098A7B2 PORT...0 CPUA...00 IPADDR. 2000:16:11:16::16:110 ADDR...00000000 00000000_7C9F6FBC LEN....000004 payload len +0000 000004F8 | ...8 ADDR...00000000 00000000_7C9F6F84 LEN....000004 RTE MTU +0000 000004F8 | ...8 ADDR...00000000 00000000_7C9F6F6C LEN....000004 dest cache +0000 00000000 | ....
Local fix
Problem summary
**************************************************************** * USERS AFFECTED: All users of the IBM Communications Server * * for z/OS Version 1 Release 13 IP: * * IPv6 * **************************************************************** * PROBLEM DESCRIPTION: ABENDS4C5 RSN74FF2000 in EZBITDSA when * * sending an IPv6 packet of 1280 bytes * * or larger without a fragment header * * and the destination is known to have * * a usable MTU of less than 1280. * **************************************************************** * RECOMMENDATION: * **************************************************************** ABENDS4C5 RSN74FF2000 in EZBITDSA when sending an IPv6 packet of 1280 bytes or larger without a fragment header and the destination is known to have a usable MTU of less than 1280. An IPv6 TCP connection sends a packet and an intermediate hop determines the packet must be encapsulated. The encapsulation grows the packet size beyond the MTU of the forwarding link and an ICMPv6 Packet Too Big message is returned to the originating TCP/IP. The ICMPv6 message also includes the usable MTU taking into account the encapsulation. When the usable MTU is less than 1280 bytes TCP will retransmit the original packet and IPv6 fails to add a fragment header. The sending logic in EZB6POUT determines the packet is to big and generates an internal ICMPv6 Packet Too Big message, driving the TCP layer to immediately retransmit the packet again. The retransmitted packet size is not adjusted and the same process repeats itself until the abend occurs. When sending a packet of 1280 bytes to a destination that has a usable MTU of less than 1280 requires the originator of the IPv6 packet to include a fragment header. The fragment header should be added in this scenario and the internal error should not be generated. +-------------------------------------------------------------+ + Please check our Communications Server for OS/390 homepages + + for common networking tips and fixes. The URL for these + + homepages can be found in Informational APAR II11334. + +-------------------------------------------------------------+
Problem conclusion
Temporary fix
Comments
EZB6POUT has been amended to add a fragment header when sending a packet that is 1280 bytes and the known usable MTU to the destination is less than 1280.
APAR Information
APAR number
PM67781
Reported component name
TCP/IP V3 MVS
Reported component ID
5655HAL00
Reported release
1D0
Status
CLOSED UR1
PE
NoPE
HIPER
NoHIPER
Special Attention
NoSpecatt
Submitted date
2012-06-27
Closed date
2012-07-24
Last modified date
2012-10-01
APAR is sysrouted FROM one or more of the following:
APAR is sysrouted TO one or more of the following:
UK80653
Modules/Macros
EZB6POUT
Fix information
Fixed component name
TCP/IP V3 MVS
Fixed component ID
5655HAL00
Applicable component levels
R1D0 PSY UK80653
UP12/09/08 P F209
Fix is available
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Document Information
Modified date:
01 October 2012