PHWinfo - Afficher un message

22/03/2006, 19h17

Rick Jones wrote:
> If part of the "bad" path is a trunked/bonded/aggregated link and
> doing something foolish like round-robin packet scheduling across the
> links the segments could be getting reordered, which would cause the
> reciever to send an immediate ACK upon reciept of each out-of-order
> segment. That ACK would be for the last in-order segment received and
> would therefore look like a duplicate.

Very insightful, Rick. The OP mentioned seeing TCP retransmissions,
but it's possible that the connection is experiencing minor packet
loss, with consistent reordering.

That is to say, maybe packets are showing up like this: 2,1,4,3,6,5,8,7

That would result in a lot of dupACKs, but not many retransmissions,
which I think is the scenario you're describing.

> If you can get cooperation from the receiver, have them take a
> snapshot of TCP statistics on the FTP server from two points during
> your FTP transfer and run them (if possible) through the likes of
> beforeafter:
>
> ftp://ftp.cup.hp.com/dist/networking/tools/
>
> and see if the receiver is reporting lots of out-of-order segments.
> Also see if they are receiving lots (for some definition of "lots"
> which would be as a percentage of total traffic) of completely
> duplicate packets.

The OP might be able to learn something by looking only at the sender's
TCP stats: If the number of TCPinDupAcks (or somesuch) is increasing
rapidly, but the number of TCPRetransmissions (or somesuch) is not,
then it sounds like a misordering problem.

> Lots of out-of-order and dups suggest either a fubar sender, or packet
> reordering in the network triggering false rtx.
>
> Lots of out-of-order without lots of dups suggest honest-to-goodness
> packet loss in the network.

I think Rick means dup *segments* in those statements, not dupACKs.

I've thought of another scenario: How sure are you that the traffic is
only going across one of your WAN links? Perhaps your HSRP primary is
sending some of the traffic to the WAN, and some of the traffic to the
other WAN router?

Can you pull the WAN cable from the WAN router 2 (.3)?

/chris

22/03/2006, 19h17	#8
googlegroups@marget.com Messages: n/a Hébergeur:	Re: TCP Duplicate ACKS Rick Jones wrote: > If part of the "bad" path is a trunked/bonded/aggregated link and > doing something foolish like round-robin packet scheduling across the > links the segments could be getting reordered, which would cause the > reciever to send an immediate ACK upon reciept of each out-of-order > segment. That ACK would be for the last in-order segment received and > would therefore look like a duplicate. Very insightful, Rick. The OP mentioned seeing TCP retransmissions, but it's possible that the connection is experiencing minor packet loss, with consistent reordering. That is to say, maybe packets are showing up like this: 2,1,4,3,6,5,8,7 That would result in a lot of dupACKs, but not many retransmissions, which I think is the scenario you're describing. > If you can get cooperation from the receiver, have them take a > snapshot of TCP statistics on the FTP server from two points during > your FTP transfer and run them (if possible) through the likes of > beforeafter: > > ftp://ftp.cup.hp.com/dist/networking/tools/ > > and see if the receiver is reporting lots of out-of-order segments. > Also see if they are receiving lots (for some definition of "lots" > which would be as a percentage of total traffic) of completely > duplicate packets. The OP might be able to learn something by looking only at the sender's TCP stats: If the number of TCPinDupAcks (or somesuch) is increasing rapidly, but the number of TCPRetransmissions (or somesuch) is not, then it sounds like a misordering problem. > Lots of out-of-order and dups suggest either a fubar sender, or packet > reordering in the network triggering false rtx. > > Lots of out-of-order without lots of dups suggest honest-to-goodness > packet loss in the network. I think Rick means dup segments in those statements, not dupACKs. I've thought of another scenario: How sure are you that the traffic is only going across one of your WAN links? Perhaps your HSRP primary is sending some of the traffic to the WAN, and some of the traffic to the other WAN router? Can you pull the WAN cable from the WAN router 2 (.3)? /chris