Size limit for PDUs

[vpalania]

Hi all,

Can anyone summarize the size limit(both max and min) for the following PDUs:

1.Ethernet Frame

2.IP

3.TCP

4.UDP

Kindly give for both headers and data.

Thanks,

Vijay

[arvindchari]

The maximum frame size for most ethernet techonologies is 1518 bytes.This varies between 1518 bytes to 1536 bytes as a result of various encapsulations used such as ISL / DOT1Q / other layer 2 encapsulation technologies. Also called the MTU

(Maximum transmission Unit) this value may be definied on most cisco switches on a per vlan basis and go right upto 9000 bytes (search for jumbo frames).

The IPv4 packet size is 32 bits and a great resource for learning about the structure of the same is

http://www.freesoft.org/CIE/Course/Section3/7.htm

For more details on TCP and UDP packet structures visit

http://mike.passwall.com/networking/tcppacket.html

and

http://mike.passwall.com/networking/udppacket.html

respectively

HTH

Arvind

[pkhatri]

Just to add to Arvind's post,

IP: the max header size is contrained by the IHL field of the IP header, which limits the header to 15 4-byte words, or 60 bytes. The total maximum header size is 65535 bytes, including the header.

TCP: Since TCP is carried in IP, the max size of a TCP segment is 65535 - 20 bytes of the TCP header = 65515 bytes. The same applies to UDP.

Hope that helps - pls rate the post if it does.

Paresh