During a transmission of Given S Data-processing S, MTU or Maximum Transmission Unit defines the maximum size (in bytes) of the Paquet which can be transmitted in only once.

The MTU is used as a basis for the negotiation of MSS (Maximum Size Segment) in the establishment of a session TCP.

The discovery of the maximum size (in bytes) of the package which can be transmitted in only once on the way of the emetor to the receiver, for example of the navigator Web to the Web server, is called " Path MTU discovery (PMTU) ". To measure this size under linux, you can use the order " tracepath " where corresponds to the distant waiter.

Example of value of MTU according to the type of network

• on Ethernet: MTU = 1500 Bytes on a Screen Ethernet of 1518 Bytes
• on PPPoE: MTU = 1492 Bytes
• on ADSL or ATM 25 PMTU = 1468 Bytes
• IPv6: MTU by defect is worth 4352 Octets
• on Token-ring: MTU = 5000
• on Frame Relay MTU is 1564

based on a MRU of 1500 for PPP according to the RFC3070.

• on the case of the local Chart network Localhost (the local English host) lo: MTU =1 6436

to make under Linux: Ping 127.0.0.1 - M C - S 16408 or: Tracepath 127.0.0.1

See too

Related articles

• For the automatic determination of the size of the MTU, to see PMTUD (Path MTU discovery)

External bonds

• RFC 1191, Path MTU Discovery

• RFC 1981, Path MTU Discovery for IP version 6
• RFC 2923, Problem TCP with Path MTU Discovery

Sources

• For MTU on Ethernet and PPPoE, to see Page of Christian Caleca]
• For MTU on IPv6, to see Page of the site livre.point6.net

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