Long and short headers

[Christopher Brown]

Folks

I know when establishing a connection/session/whatever we start with a long header as its needed for the handshake. Then later I see we move to a short header.

Is there ever the use case, where the start of a new flow ( 4 tuple ) would START with a short header packet. 

From reading the spec , I had assumed yes and they would be tied together with the connection ID - however from looking at traffic any new 4 tuple seems to always start with a long header.

So for example - 1 video, 2 UDP flows , same client and server. 

Is it the case that a handshake needs to happen, even if the hosts remain the same but only source port is changing?

thanks

Chris

[Nick Harper]

The start of a connection needs a handshake, which uses the long packet header. Once the connection is established, it can migrate to a different 4-tuple, in which case the only packets sent on that 4-tuple will use the short packet header.

Based on what you described, it sounds like you're observing a client make multiple connections to the same server, rather than seeing connection migration.

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[Christopher Brown]

thank you for the reply, yes i agree.

Though i am curious as to whether connection migration is currently on. I have some network traffic captures and see no 'new flows', where the first packet is a short header.  - new flow defined as a conversation in wireshark ( which is the 4 tuple ).

Thanks

Chris