Bug ID 528734: TCP keeps retransmitting when ICMP Destination Unreachable-Fragmentation Required messages are received.

Last Modified: Oct 10, 2018

Bug Tracker

Affected Product:  See more info
BIG-IP LTM(all modules)

Known Affected Versions:
11.5.1, 11.5.1 HF1, 11.5.1 HF10, 11.5.1 HF11, 11.5.1 HF2, 11.5.1 HF3, 11.5.1 HF4, 11.5.1 HF5, 11.5.1 HF6, 11.5.1 HF7, 11.5.1 HF8, 11.5.1 HF9, 11.5.2, 11.5.2 HF1, 11.5.3, 11.5.3 HF1, 11.5.3 HF2, 11.5.4, 11.5.4 HF1, 11.5.4 HF2, 11.6.0, 11.6.0 HF1, 11.6.0 HF2, 11.6.0 HF3, 11.6.0 HF4, 11.6.0 HF5, 11.6.0 HF6, 11.6.0 HF7, 11.6.0 HF8, 11.6.1, 12.0.0, 12.0.0 HF1, 12.0.0 HF2, 12.0.0 HF3, 12.0.0 HF4

Fixed In:
12.1.0, 11.6.1 HF1, 11.5.4 HF3

Opened: Jun 18, 2015
Severity: 3-Major
Related AskF5 Article:
K04711825

Symptoms

In a Standard virtual server, a data segment will be retransmitted when an ICMP Type 3, Code 4, message with an MTU (greater than or equal to 0) is received. The retransmission occurs until there are no ICMP Type 3, Code 4 messages, a connection times out, or an ACK is received.

Impact

Packets might fill up the pipe and cause a minor outage.

Conditions

Router or client sends ICMP frag messages with random MTU values. It can be increasing, decreasing, same, or 0 MTU.

Workaround

None.

Fix Information

TCP drops the second or later ICMP Type 3, Code 4 message. If the second packet is a valid ICMP packet, the downstream router will send another ICMP Type 3, Code 4 message.

Behavior Change