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Bug #1655

closed

Redmine webserver: Path MTU Discovery does not work

Added by Junxiao Shi over 11 years ago. Updated over 11 years ago.

Status:
Closed
Priority:
Normal
Assignee:
-
Category:
-
Start date:
06/09/2014
Due date:
% Done:

0%

Estimated time:

Description

Steps to reproduce:

  1. connect a laptop to a router; this link has MTU=1396
  2. use tcpdump to capture on the link between router and the outside world; this link has MTU=1500
  3. on the laptop, run wget http://redmine.named-data.net/

Expected: HTTP response reaches the laptop

Actual: after sending HTTP request, wget keeps waiting for response

tcpdump capture reveals:

  1. TCP packets from Redmine webserver are 1416 octets each (including IPv4 header), with "Don't Fragment" flag set
  2. The router responds ICMP "Fragmentation Needed" message
  3. Redmine website retransmits TCP packets; those packets are still 1416 octets each with DF flag set

To resolve this bug, either unset DF flag, or configure the firewall and webserver to respond to "Fragmentation Needed" flag correctly

Files

Download all files
redmine.pcap (20.1 KB) redmine.pcap tcpdump when accessing Redmine (bug) Junxiao Shi, 06/09/2014 07:21 PM
jenkins.pcap (4.58 KB) jenkins.pcap tcpdump when accessing Jenkins (reference) Junxiao Shi, 06/09/2014 07:21 PM
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