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I am Val Glinskiy, network engineer specializing in data center networks. TIME magazine selected me as Person of the Year in 2006.

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Wednesday, February 04, 2009

Packetization Layer Path MTU Discovery

A lot of network administrators block all ICMP traffic on the network's edge. Although some ICMP packets can be used in DDoS, ICMP type 3 plays important role in Paht MTU discovery. If ICMP is completely blocked, sending side can not reliably determine MTU and that can lead to re-transmissions and slower data transfer. Sometimes, ICMP blocking network could be outside your control, so you can not change ACL or firewall rules. In this case Packetization Layer Path MTU Discovery can be used. It utilizes TCP for maximum packet size discovery (RFC4821). To enable PLPMTUD on Linux:
echo 2 > /proc/sys/net/ipv4/tcp_mtu_probing
in /etc/sysctl.conf net.ipv4.tcp_mtu_probing = 2

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