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Poor network performance

Acronyms:

DHCP - Dynamic Host Configuration Protocol
HTTPS - Hyper Text Transfer Protocol Secure sockets
ICMP - Internet Control Message Protocol
ISP - Internet Service Provider
MTU - Maximum Transmission Unit
PMTU - Path MTU Discovery
PPPoE - Point-to-Point Protocol Over Ethernet
RFC - Request for Comments
SSL - Secure Sockets Layer
WAN - Wide Area Network

Problem:

Poor performance on some internet applications such as:

  • Video streaming
  • Some HTTPS sites do not function correctly.
  • Some SSL communications do not function correctly.
  • General throughput seems lower compared to a previous router.

Solution:

Go to Network Connections -> WAN Ethernet (WAN PPPoE) -> Settings -> MTU

Change the MTU from Automatic or Automatic (DHCP) to Manual and adjust the value to 1500 for Cable and 1492 for DSL.

Explanation:

We have found that some ISPs are blocking the ICMP notifications that are required for PMTU to work correctly; by RFC1191 section 3.1 definition, PMTU can not send over a MTU of 576 unless the other side it is connected to authorized a larger MTU. Because the ICMP notifications are blocked no authorization takes place and PMTU falls back to 576 per the RFC definition.

A copy of the RFC can be located here: http://www.ietf.org/rfc/rfc1191.txt


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