Subject: Re: [Tsvwg] Re: Limited Slow-Start for TCP with Large Congestion Windows

From: stanislav shalunov <[email-masked]>
Date: 02 Aug 2002 03:17:06 -0400

Mark Allman <[email-masked]> writes:

> I am not familiar with the implementation at all, so I am trying to
> understand this....  My workstation has one route entry --- all
> traffic goes one way.  So, does that mean that all my connections
> share some cached ssthresh value?  That would not seem right to me.

I don't know what OS your workstation is running, but if the stack is
BSD-based, you might have the feature that is being discussed.  On my
ancient FreeBSD laptop, I see this:

shalunov@cain$ netstat -nr
Routing tables

Internet:
Destination        Gateway            Flags     Refs     Use     Netif Expire
default            216.254.censored   UGSc       10        1      wi0
127.0.0.1          127.0.0.1          UH          0  3610838      lo0
[Two local Ethernet routes.]

But this doesn't include cloned route entries (which would be
displayed with `netstat -nar').  However, if I look carefully at the
(cloned -- i.e., automatically inserted by the OS on first connection)
route to my mail server, I see this:

shalunov@cain$ route -n get mail
   route to: 209.211.239.218
destination: 209.211.239.218
    gateway: 216.254.censored
  interface: wi0
      flags: <UP,GATEWAY,HOST,DONE,WASCLONED>
 recvpipe  sendpipe  ssthresh  rtt,msec    rttvar  hopcount      mtu     expire
       0         0      2976       188       250         0      1500         0 

> On the other hand, if all my connections to a.b.c.d share an
> ssthresh value that seems more reasonable.

This is what happens.  (They also share other variables as can be
seen; the route expires after some timeout, of course.)

-- 
Stanislav Shalunov		http://www.internet2.edu/~shalunov/

"The power of accurate observation is commonly called cynicism by
those who have not got it."			-- G. B. Shaw

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