tcp info

tcp info

Post by Bruno Gervas » Thu, 21 May 1998 04:00:00



Can anyone tell me what causes these messages:

14:36:42.111662 arp who-has 192.84.162.2(Broadcast) tell
EXTERNALWEB.help.com
14:36:42.922072 GRIERSON.help.com.970 > EXTERNALWEB.help.com.32783: udp
40 (DF)
14:36:42.923595 EXTERNALWEB.help.com.32783 > GRIERSON.help.com.970: udp
136 (DF)
14:36:43.051675 arp who-has 192.84.162.2 (Broadcast) tell
EXTERNALWEB.help.com

It seems that I get alot of those.

--
-----------------------------
NATIONAL FILM BOARD OF CANADA

BRUNO GERVASI              ----
System Administrator      /    \
                          \ () /
3155 Cote De Liesse Rd.    ----
St.Laurent, Qc            / __ \
Canada H4N 2N4            | /\ |
TEL   : +514-283-9094     | || |
FAX   : +514-283-9819     |_||_|

-----------------------------

 
 
 

tcp info

Post by fl.. » Thu, 21 May 1998 04:00:00


: --------------474144BDA5A7C9C9650B48B6
: Content-Type: text/plain; charset=us-ascii
: Content-Transfer-Encoding: 7bit
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Don't do this, it's annoying.

: Can anyone tell me what causes these messages:

: 14:36:42.111662 arp who-has 192.84.162.2(Broadcast) tell
: EXTERNALWEB.help.com

Externalweb.help.com wants to talk to the machine at 192.84.162.2.  It has
decided that this machine is on its local net, so it is trying to find out
the link-layer (probably ethernet) address.  Towards this end, it is
sending out an Address Resolution Protocol (ARP) query.

: 14:36:42.922072 GRIERSON.help.com.970 > EXTERNALWEB.help.com.32783: udp
: 40 (DF)
: 14:36:42.923595 EXTERNALWEB.help.com.32783 > GRIERSON.help.com.970: udp
: 136 (DF)

Grierson and externalweb are doing a small transaction.  It's hard to say
what, without more information.  If grierson is a unix box, then the
process on its side is probably a system/privileged process, because
binding to ports under 1024 requires privilege.  I wonder if this is part
of a longer sequence, because it's more common to see transactions
initiated by non-privileged, high-port client processes and served by
privileged, low-port server processes.

: 14:36:43.051675 arp who-has 192.84.162.2 (Broadcast) tell
: EXTERNALWEB.help.com

Externalweb didn't get an answer to its ARP query, so it sent it again.
Eventually it will time out.

: It seems that I get alot of those.

Is 192.84.162.2 on the same ethernet segment as externalweb?  If so, you
need to determine why it's not responding to ARP queries.  If not, you
need to reconfigure externalweb to have a better idea of where to find it.

--

 Ben

<Just Another System Administrator>

 
 
 

1. TCP: info about client

Hi there,

I have a small question I would appreciate some hints to. It is not a problem
yet, but it may well turn out to become a problem if I don't solve it properly.

Anyway, I have a server that accepts connections on TCP-sockets from various
clients. I would like to know the hostname of the client after the connection
has been established. With hostname I mean in this case a char * such as:
"example.foo.com".

What functions can be used for the purpose? I'm a little bit lost here, but I
only need the names of the functions, I can check the usage on the man-pages or
in the fabulous Stevens book.

Also, can these functions block when fetching the hostname? I need to query the
names fast and without blocking for a nameserver query. If they block I'll just
put the functionality in a dedicated thread and have the main server queue
requests which the thread the performs as fast as it can.

The used system is Linux 2.2.12 with glibc 2.1. I'd appreciate any hints or
links to the proper RTFM-resources.

        Regards,
        Chakie

--
---------------------+------------------------------------------------------
 Jan 'Chakie' Ekholm |    CS at ?bo Akademi University, Turku, Finland
    Linux Inside     | I'm the blue screen of death, no-one hears you scream

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