First ping response receiving late

I am trying to ping the Gateway which is on RF network, the first ping
response getting delayed, the first response is received after it
sends second ICMP message to destination, this way everytime first
ping response getting delayed. out of 20 pings, only 19 receives in-
time, where as first one comes very late (after it timesout). Any
idea, Is it because it is ICMP message, not a high priority messge,
that is why it might receive late. Thanks in advance.

(E-Mail Removed) wrote:
> I am trying to ping the Gateway which is on RF network, the first ping
> response getting delayed, the first response is received after it
> sends second ICMP message to destination, this way everytime first
> ping response getting delayed. out of 20 pings, only 19 receives in-
> time, where as first one comes very late (after it timesout). Any
> idea, Is it because it is ICMP message, not a high priority messge,
> that is why it might receive late. Thanks in advance.
>
The first ping will get converted to an ARP if the machine doesn't
already know the MAC address of the gateway.

Robert Harris <(E-Mail Removed)> wrote:
> (E-Mail Removed) wrote:
> > I am trying to ping the Gateway which is on RF network, the first ping
> > response getting delayed, the first response is received after it
> > sends second ICMP message to destination, this way everytime first
> > ping response getting delayed. out of 20 pings, only 19 receives in-
> > time, where as first one comes very late (after it timesout). Any
> > idea, Is it because it is ICMP message, not a high priority messge,
> > that is why it might receive late. Thanks in advance.
> >
> The first ping will get converted to an ARP if the machine doesn't
> already know the MAC address of the gateway.

It isn't converted so much as "will wait for ARP resolution." As would
subsequent ICMP echo requests. Still, I suspect there may be some
additional stuff happening with the RF network, ARP resolution does
not (IIRC) result in packet re-ordering.

One way to test would be to note the remote MAC, delete the ARP entry
and replace it with a permanent one set from the command line, then
try the ping test again. Repeat on the other end for going the other
direction. Then run the ping test and see if the first one remains
delayed.

rick jones
--
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The real question is "Can it be patched?"
these opinions are mine, all mine; HP might not want them anyway...
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Rick,

Thanks. I already have ARP entry, I got an IP address, then I tried to
ping the gateway, the first ping response is delayed everytime.

(E-Mail Removed) wrote:
> Thanks. I already have ARP entry, I got an IP address, then I tried to
> ping the gateway, the first ping response is delayed everytime.

Does/did the gateway always have an ARP entry for _your_ IP?

Trying with something other than ping could be interesting. A netperf
UDP_RR test perhaps, or TCP_RR - although with the TCP_RR test, before
the requests and responses start to flow the SYN segments will have
been exchanged so those would be the "first" packets in the flow.
Still, if you ./configure --enable-histogram netperf you could try
that or a UDP_RR test:

netperf -t UDP_RR -H <remote> -v 2

and then look at the resulting histogram.

There could still be the issue of the control connection affecting the
initial packet behaviour though.

rick jones
--
denial, anger, bargaining, depression, acceptance, rebirth...
where do you want to be today?
these opinions are mine, all mine; HP might not want them anyway...
feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH...

On Wed, 12 Sep 2007, in the Usenet newsgroup comp.os.linux.networking, in
article <(E-Mail Removed) om>,
(E-Mail Removed) wrote:

>I am trying to ping the Gateway which is on RF network, the first ping
>response getting delayed, the first response is received after it
>sends second ICMP message to destination, this way everytime first
>ping response getting delayed. out of 20 pings, only 19 receives in-
>time, where as first one comes very late (after it timesout).

What operating system?
What type of RF network?
What version of ping?
What is the EXACT command used?
What is the exact output for the first three packets?
What does a packet sniffer show?
What does '/sbin/arp -a' show before and during the ping?

>Any idea,

Not enough information. Could be a lot of different things. Is the
RF link up/active when the first ping attempt occurs, or does the link
have to wake up? Does using 'ping -n IP.of.Gate.way' make any
difference?

>Is it because it is ICMP message, not a high priority messge, that is
>why it might receive late.

Depends on the network stack configuration and/or traffic conditioning.
Use a packet sniffer, and compare the ping attempts with attempting to
connect to ANY open or closed port on the gateway using a TCP based
service like telnet (example - 'telnet IP.of.Gate.way 70' which would
attempt to establish a connection to port 70 [gopher] which should be
closed - does the system come back immediately with a 'Connection
refused' error message).

Old guy