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Hitachi Gigabit Router GR2000 Series Enhanced Version Operations - Device Management Overview

7-48 GR2K-GA-0015

Ver. 07-02

7.5.3.6 Setting Value for mru (MTU)

It is possible that a particular HP will be inaccessible even though the configuration

definition (mru value) of PPPoE was not changed. The solution for this is to change

the mru (MTU) size. Shown below are examples of communication impediments in

Flets ADSL and B Flets service, as well as the procedure for changing the mru (MTU)

size.

Example: In the PPPoE including the Flets ADSL and B Flets service, the MTU uses

1454 bytes. The MTU used in general Ethernet uses 1500 bytes.

An error may occur if this packet size does not remain constant. This could cause

a blockage in data flow even if a connection was already established with the

server. Try an operation in which you adjust this device’s mru (MTU) value.

Procedure for changing the mru (MTU)

Confirm the setting value of mru for the PPPoE information by using the

configuration definition show pppoe command.

[Result of the execution]

7.5.3.7 Setting Value of mss Information

It is possible that a particular HP will be inaccessible even though the configuration

definition (MSS value) of PPPoE was not changed. This occurs when the data size

exceeds the upper limit of the size of a receivable signal. The MSS size change and

the changing procedure are given below.

Changing the MSS size

The MTU for Ethernet is normally 1500 bytes, whereas MSS must be 1460 bytes

to allow for the communication (TCP/IP) header size (40 bytes) plus data size

(MSS).

[MSS (1460) = MTU (1500) - (40 TCP/IP header size)

However, since the PPPoE header (8 bytes) is added to the PPPoE line on the WAN

side, the header data size generates an overflow causing a fragment. As a result,

performance decreases a packet may be abolished by the black hole router

present in the communication path, rendering a particular home page

un-viewable. This problem cannot be resolved in this device unless MSS size is

changed on both the up and down packets.

Set a value smaller than the current

setting value.

Input the next command to make the setting

information effective.

current mru value.

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Hitachi GR2000 Series Manual do Utilizador Página 214