Re: ICMP's & IP src addrs


Tait Cyrus (hi.unm.edu!cyrus@hc.dspo.gov)
20 Sep 88 00:23:08 GMT


In article <22185@sgi.SGI.COM> vjs@rhyolite.SGI.COM (Vernon Schryver) writes:
>In article <24915@bu-cs.BU.EDU>, kwe@bu-cs.BU.EDU (kwe@bu-it.bu.edu (Kent W. England)) writes:
>> No, no, no. ICMP messages are special, because they are error
>> messages. They must be treated carefully and conservatively.
>
>That means my favorite diagnostic tool and stress test will go away:
>`ping -f <broadcast>', where 'ping' takes '-f' as 'flood the target at
>100 packets/sec.' (100 p/s * >100 hosts = ?) Believe it or not, this
>can be quite useful for constructive purposes. Tho it will break my
>heart, this tool should go to the same retirement home as the old
>Atoms-for-Piece plan for digging a new Panama canal.
>
>The usefulness of the relatively innocuous 'ping <broadcast>' to see
>what's there can be duplicated with a small program which sends to all
>possible host addresses (paying attention to netmask). Modern machines
>can generate at least a couple hundred packets/sec from user code. (At
>least our's and our competator's are much better than that. :-) Thus
>in any situation where you don't expect too many responses for the test
>to social acceptible, it would take the new program only seconds to do
>the same thing.

I agree, though there are some problems. I have a class B address
with a netmask giving me 2k possible addresses. Assuming 100 p/s,
that is about 20 seconds. Although this is not a very long period of
time, you would never see this speed because for each IP address,
your machine has to arp the IP address. Since most IP addresses are
not used, at least on our net at the current time, a lot of time
would be spent waiting for the arp replies. Besides, I would
probably blow out my machines arp table with 2k entries.

As far as what the correct response to such a "request" should be,
we will have to wait for the new hosts requirements RFC (any ideas
where I can get a copy of the draft???).

>Vernon Schryver -- Silicon Graphics

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