Re: demand dialing

Moe Trin <ibuprofin@xxxxxxxxxxxxxxxxxxxxxx> wrote:
Hi Clifford!
:)
On Sun, 5 Aug 2007, in the Usenet newsgroup comp.os.linux.networking,
in article <4ob59f.u71.ln@xxxxxxxxxxxxxxxxxxxx>, Clifford Kite wrote:

Are you still in contact with Paul? As this is a Linux only mode, I'm
not sure James would be interested.

No, I dropped out of the linux-ppp mailing list some time ago and haven't
been in a hurry to get back in - it seemed to generate a lot of spam.

The only other reason I know that might cause that message appearing
instantly with a default route present is the absence of nameservers
in resolv.conf.

I'm not so sure - the original posting said:

]>% ping foo.com
]>Host unreachable. <-- instant

A DNS problem would be "unknown host", would it not? "Host Unreachable"
says that it knows an IP, but either the gateway is dead, or the
destination host (or something in-between)is returning an ICMP Unreachable.

I think the message is whatever the coder (or whomever) wants it to be.
And yes, I'm more comfortable with "unknown host" in cases where a FQDN
cannot be resolved but if the FQDN can't be resolved then the host is
also unreachable.

'(outbound and not (icmp[0] = 3))'

so that the timer ignores inbounds and any ICMP Type 3 (unreachable) in
either direction.

I'm not sure what you have in mind but there doesn't seem to be a type 3
for code 0, only a type 0. Stevens Vol 1..

Blame that on the confusion surrounding the tcpdump man page.

I think I'll blame my preceding remark on _my_ confusion. You are right,
it has to be icmp(0)=type and icmp(1)=code.

I'm reading
that '[0]' as the byte offset relative to the protocol layer, hence the
example

To print all ICMP packets that are not echo
requests/replies (i.e., not ping packets):
tcpdump 'icmp[0] != 8 and icmp[0] != 0"

Which is correct. Tcpdump expressions always did give me a headache.

FYI, the tcpdump man pages here (April 2005) explain the usage better
and introduce names that can be used as arguments. In particular above
example is presented as

To print all ICMP packets that are not echo
requests/replies (i.e., not ping packets):
tcpdump 'icmp[icmptype] != icmp-echo and icmp[icmptype] != icmp-echoreply'

Are we having fun yet? ;-)

:%P

--
Clifford Kite
/* "They that can give up essential liberty to obtain a little temporary
safety deserve neither liberty nor safety." Benjamin Franklin */

.

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