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[Bug 1889943] Re: Improper TCP/IP packet splitting on e1000e/vmxnet3

From: Launchpad Bug Tracker
Subject: [Bug 1889943] Re: Improper TCP/IP packet splitting on e1000e/vmxnet3
Date: Wed, 07 Jul 2021 04:17:19 -0000

[Expired for QEMU because there has been no activity for 60 days.]

** Changed in: qemu
       Status: Incomplete => Expired

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  Improper TCP/IP packet splitting on e1000e/vmxnet3

Status in QEMU:

Bug description:
  Update: The sw implementation of fragmentation also creates malformed
  IPv6 packets when their size is above the MTU. See comment #3

  Problem Description:
  When using a tap interface and the guest sends a TCP packet that would need 
to be segmented, it is fragmented using IP fragmentation. The host does not 
reassemble the IP fragments and forwards them to the next hop. This causes 
issues on certain ISPs, which seemingly reject IP fragments(Verizon Fios).
  This issue occurs on the e1000e and vmxnet3 NIC models, and possibly others. 
It does not occur on the virtio(which passes the entire packet through to the 
host w/o fragmentation or segmentation) or the e1000 model().

  Test scenario:
  Setup a tap and network bridge using the directions here: 
  Boot the machine into any modern guest(a Fedora 31 live iso was used for 
  Begin a wireshark capture on the host machine
  On the host(or another machine on the network) run: npx http-echo-server(See 
  On the guest run
  Curl -d “Lorem ipsum dolor sit amet, consectetur adipiscing elit. Maecenas 
venenatis viverra ipsum, ac tincidunt est rhoncus eu. Suspendisse vehicula 
congue ante, non rhoncus elit tempus vitae. Duis ac leo massa. Donec rutrum 
condimentum turpis nec ultricies. Duis laoreet elit eu arcu pulvinar, vitae 
congue neque mattis. Mauris sed ante nunc. Vestibulum vitae urna a tellus 
maximus sagittis. Vivamus luctus pellentesque neque, vel tempor purus porta ut. 
Phasellus at quam bibendum, fermentum libero sit amet, ullamcorper mauris. In 
rutrum sit amet dui id maximus. Ut lectus ligula, hendrerit nec aliquam non, 
finibus a turpis. Proin scelerisque convallis ante, et pharetra elit. Donec 
nunc nisl, viverra vitae dui at, posuere rhoncus nibh. Mauris in massa quis 
neque posuere placerat quis quis massa. Donec quis lacus ligula. Donec mollis 
vel nisi eget elementum. Nam id magna porta nunc consectetur efficitur ac quis 
lorem. Cras faucibus vel ex porttitor mattis. Praesent in mattis tortor. In 
venenatis convallis quam, in posuere nibh. Proin non dignissim massa. Cras at 
mi ut lorem tristique fringilla. Nulla ac quam condimentum metus tincidunt 
vulputate ut at leo. Nunc pellentesque, nunc vel rhoncus condimentum, arcu sem 
molestie augue, in suscipit mauris odio mollis odio. Integer hendrerit lectus a 
leo facilisis, in accumsan urna maximus. Nam nec odio volutpat, varius est id, 
tempus libero. Vestibulum lobortis tortor quam, ac scelerisque urna rhoncus in. 
Etiam tempor, est sit amet vulputate molestie, urna neque sodales leo, sit amet 
blandit risus felis sed est. Nulla eu eros nec tortor dapibus maximus faucibus 
ut erat. Ut pharetra tempor massa in bibendum. Interdum et malesuada fames ac 
ante ipsum primis in faucibus. Etiam mattis molestie felis eu efficitur. Morbi 
tincidunt consectetur diam tincidunt feugiat. Morbi euismod ut lorem finibus 
pellentesque. Aliquam eu porta ex. Aliquam cursus, orci sit amet volutpat 
egestas, est est pulvinar erat, sed luctus nisl ligula eget justo vestibulum.” 

  2000 bytes of Lorem Ipsum taken from https://www.lipsum.com/

  Compare results from an e1000, a virtio, and a e1000e card:
  | Model  | Fragment  | Segment | Wire Size  |
  | e1000e | Yes       | NO      | 1484 + 621 |
  | e1000  | No        | Yes     | 1516 + 620 |
  | Virtio | NO        | NO      | 2068       |

  Expected Results:
  TCP Segment to proper size OR pass full size to host and let the host split 
if necessary.

  Configuration changes that did not work:
  Disable host, guest, router firewalls
  Different Hosts
  Different Physical NICs
  Libvirt based NAT/Routed modes
  Fedora 32 vs 31
  Qemu 4.2.0 vs github commit d74824cf7c8b352f9045e949dc636c7207a41eee

  System Information:
  lsb_release -rd
  Description:  Fedora release 32 (Thirty Two)
  Release:      32

  uname -a
  Linux pats-laptop-linux 5.7.10-201.fc32.x86_64 #1 SMP Thu Jul 23 00:58:39 UTC 
2020 x86_64 x86_64 x86_64 GNU/Linux

  I can provide additional logs, debug info, etc. if needed.

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