Path: utzoo!utgpu!attcan!uunet!lll-winken!ncis.llnl.gov!ncis!helios.ee.lbl.gov!pasteur!agate!ucbvax!SRI-NIC.ARPA!TYSON
From: TYSON@SRI-NIC.ARPA (Mabry Tyson)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: SYNs that don't get ACKed
Message-ID: <12463383654.24.TYSON@SRI-NIC.ARPA>
Date: 18 Jan 89 00:51:11 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Reply-To: Tyson@AI.SRI.COM
Organization: The Internet
Lines: 47

>Date:     Mon, 16 Jan 89 13:50:41 EST
>From:     lane (Charles Lane) @ DUPHY4.Drexel.Edu
>Subject:  SYNs that don't get ACKed
>To:       tcp-ip @ DUPHY4.Drexel.Edu

>The best explanation that I can come up with is that the ACK SYN's
>aren't getting back to CRVAX.  Could this be a routing problem?
>We've observed this behaviour with a number of hosts, and the best
>explanation we've thought of so far is that the packets are coming in
>over a `good' route and going out over a `bad' route.


[Note, while I am at SRI, I don't have any control or direct access to 
CRVAX.SRI.COM or SRI-GW.ARPA.]

I looked into the problem of connecting between SRINET and DREXEL
today.  From IU.AI.SRI.COM (on the Arpanet directly), I could ping
129.25.1.103.  The response time was on the order of 1 to 4 seconds.
I set up another host (that is on SRINET) to go through the same
gateway that CRVAX.SRI.COM uses (SRI-GW.ARPA).  When I tried to ping
from there, I couldn't get through (and got a message from SRI-GW
indicating that destination was an unreachable network).

From IU, I found out that it was going through JVNCA.CSC.ORG to get to
DREXEL.  That immediately set off alarms for me as we had routing
problems to RUTGERS behind the same gateway a week or so earlier.

As I recall, on one day, our EGP info was that we should use JVNCB.CSC.ORG
to get to Rutgers but we couldn't get through.  If we changed it to
route through JVNCA, we got through.  (On the previous day, the problem
was exactly reversed: EGP told us to use JVNCA but packets to it didn't
work while JVNCB did work.)  At that time, JVNCB had an arpanet
address (according to domain info) of 10.18.0.16.  Now when I look up
that host, it no longer shows an Arpanet address.

I don't know what route SRI-GW.ARPA is using to get to DREXEL.  Maybe it,
or the gateway it routes to still, thinks it should try JVNCB.CSC.ORG
(on the old(?) Arpanet address)???  I suspect the situation with the JVNCnet
is in flux and you should be patient with it for awhile.

P.S.  FYI: The network configuration at SRI will be changing beginning
on Feb. 11.  I think SRI-NIC.ARPA will be basically unaffected but
network connectivity to all other hosts at SRI may encounter problems.
SRI will be available through BARRNET (part of NSFNet) when the
Arpanet dies (which looks like it will be sooner than I think it
should be!) but it isn't yet set up.
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