-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] On Behalf Of
Priscilla Oppenheimer
Sent: Monday, August 21, 2000 10:35 AM
To: Derek CHUNG; [EMAIL PROTECTED]
Subject: Re: Is a TCP packet encapsulated by a IP packet which is inside a
Layer 2 frame?
<<snip>>
Now Chuck said that nobody could rattle off header contents off the top of
their head. I'm going to see if I can. &;-)
CL: I believe I asked ( rhetorically ) how many could do what you did so
well without referring to a chart or some other source. I think even Howard
admitted he cannot do so at present? ( even if he was able to at one time )
IP
Version
Header Length
Type of Service -- precedence, etc.
Length of Packet
ID -- all fragments have the same ID
Flags -- don't fragment, more fragments
Fragment Offset -- indicates the position of this data relative to the
beginning of a fragmented message
Time to Live -- decremented by each router until it reaches 0, in which
case the packet is trashed
Protocol -- next layer up, for example, UDP, TCP, EIGRP, OSPF, ICMP, etc.
Header checksum
Source IP Address
Destination IP Address
Options -- record route, source routing, etc.
Padding if necessary -- must end on a 32-bit boundary
CL: agrees with the source I am checking this against
TCP
Source Port
Destination Port
Sequence Number -- each BYTE is sequenced. This field specifies the seq #
of the first byte in this message
ACK Number
Header Length
Flags - Urgent, ACK, PUSH, RESET, SYN, FIN
Window Size
Checksum - checksum of header and data
Urgent Pointer -- points to any urgent data in the message
Options
CL: WOW!!!
Whew! Did it! &;-)
CL: yes you did, PO, and therefore you are entitled to ask the rest of us
how we ever got such and such a certification without knowing this ;->
Still wondering how many CCIE's are unable to duplicate your feat. :->
Priscilla
At 03:59 AM 8/20/00, Derek CHUNG wrote:
>Is a TCP packet (layer 4) encapsulated by a IP packet (layer 3) which is
>inside a Layer 2 frame?
>If so, why the headers of a IP packet and TCP packet look so similar and
>redundant?
>
CL: I also believe that this premise remains untrue. While both IP and TCP
headers are normally 20 bytes, I see very little else in common, as
befitting the very different functions they perform. TCP has more
reliability functions built in - acknowledgement, windowing, etc. whereas IP
is more oriented towards best effort delivery across an internet.
>___________________________________
<<snip>>
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