Does rcp support TCP Window Scaling (RFC1323)

[Satyavrat Purohit]

On HPUX 11i, has anyone any experience with using rcp options -S and
-R ?

eg.

rcp -S 131072 -R 131072 bar user@foo:/foo/bar

I was expecting this to result in TCP Window Scaling factor of 2. The Window Scale option does appear within the SYN/SYN_ACK but the window scaling appears to be set to 0 (the option looks like 0x"030300" i.e. window scale of 2**0 = no window scale)

I hadn't modified ndd tcp_recv/xmit_hiwater_def/lnp/lfp values and I'm testing it over a LAN. HPUX doc suggests that all you need to do is set so_recvbuf and you get the window scaling you need and from rcp documentation it seemed that the -S and -R options were designed to do just that. It doesn't seem to work that way though.

Separately, I tried setting tcp_recv/xmit_hiwater_def to 131072. This resulted in the source host advertising a scaled window, but the dest host still responds with an unscaled window.

The ONLY way I could get rcp to do tcp window scaling was -
1. Set tcp_recv_hiwater_def = 131072
2. issue a "pull" rcp rather than a push i.e. rcp .

This results in the initiator advertising a recv window scale of 2 (0x"030302"). The responder still exhibits the lame 0x"030300" i.e. no window scaling, but since the initiator is the receiver of the file it works fine and I can observe close to 131072 (128K) of outstandin TCP window being pulled.

There is no need to specify -R or -S in this case (in fact I'm beginning to suspect that -R/-S have a max of 65535 and if you supply a higher value it gets cut down)

Any authoritative knowledge of RCP (how far will -R -S go towards a larger TCP window) and any real experience making RFC 1323 work for RCP would be appreciated.

Thanks

[rick jones]

Certainly older versions of rcp (and ftp) didn't do more than 56 KB socket buffers no matter what size of option you used.

To make sure that you have a new enough version (I know patches happened for FTP, but I'm not sure if they did for rcp) you should try taking a tusc trace of an rcp session and look for the setsockopt() calls.

(When I asked for the patches, I also asked that a value of "0" mean "take the system default." I don't recall if they actually implemented that, I think they've left the default to 56K)

ftp://ftp.cup.hp.com/dist/networking/tools/ has the latest 7.6 version of tusc.

If you want to make sure that automagic enabling of window scaling happens, you can install netperf and run a TCP_STREAM test setting -s and -S to say 128K

http://www.netperf.org/