From: Ruhai Wang (wangnewton2000@yahoo.com)
Date: 04/13/04
Message-ID: <20040413231056.17337.qmail@web40811.mail.yahoo.com> Date: Tue, 13 Apr 2004 16:10:56 -0700 (PDT) From: Ruhai Wang <wangnewton2000@yahoo.com> Subject: tcptrace How to change the size of TCP/IP segments/packets
We are running some file transfer experiments using
FTP/TCP/IP/PPP between two Linux PCs (running Red-Hat
Linux 7.3 with kernel 2.4.18-3). We are trying to
change the PPP MTU size (using "ifconfig ppp0 mtu
xxx"). The situation is described below:
(1) When we change the MTU to a size which is smaller
than the default size 1500 bytes, it works using the
new size, which can be observed from SYN, SYN-ACK
exchange and TSG plots.
(2) When we change the MTU to a size larger than the
default 1500 bytes (such as 4352 bytes), the protocol
still sends data using the default size of 1500
instead of the updated larger size.
I think the problem is that segments/packets delivered
to PPP are limited to less than or equal to 1500
bytes. So even though we enlarged PPP MTU, the PDU
delivered to PPP by TCP/IP is not larger than 1500
bytes.
Could anyone advise us how we can adjust the size of
TCP/IP segments larger than the default size of 1500
bytes so that the transmitted PPP frame size is
larger?
Any help will be greatly appreciated.
Ru
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