RE: [lwip-users] What is the different between IP_PROTO_UPPLITE and IP_PROTO_UDP(regular)????

[Kelly Chan]

Hi Florian,

Very good explanation. BTW, your works on porting Lwip to win32 really speed
up our project activities as we can easily use it as our unit testing
environment............

Thanks!

Kelly

-----Original Message-----
From: address@hidden
[mailto:address@hidden
Behalf Of Zschocke, Florian
Sent: Friday, July 04, 2003 8:23 AM
To: 'Mailing list for lwIP users'
Subject: AW: [lwip-users] What is the different between IP_PROTO_UPPLITE
and IP_PROTO_UDP(regular)????


Kelly Chan wrote on Freitag, 4. Juli 2003 16:09:


> I am a little confused as I don't understand the motivation
> behind two version of UDP IP Protocol: IP_PROTO_UDP &
> IP_PROTO_UDPLITE.

UDP packets of the type IP_PROTO_UDP have a checksum calculated over the
complete UDP packet, i.e. the UDP header plus the payload. UDP packets of
the type IP_PROTO_UDPLITE have a checksum calculated ONLY over the UDP
header but not over the payload of the UDP packet.

> Also, how does the receiver side know which version shall adopt
> when a UPD packet arrive (According to RFC792, the transmission
> protocol does not have version field)???

UDPLITE is a different protocol type than UDP is. In the IPv4 header the
"protocol" field will have different values for UDP and UDPLITE: UDP is
protocol 17, UDPLITE is 170, just like the IP_PROTO_UDP(LITE) defines. For
both a checksum of 0 means no checksum at all.

> On top of that, the IP_PROTO_UDP has a flag with NO_CHECK_SUM
> but the codes still perform checksum???

Where, udp_send() in udp.c? No, a checksum is not calculated if
UDP_FLAGS_NOCHKSUM is set in the PCB.

Florian.


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