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From Joshua Banks <>
Subject Re: [users@httpd] Apache problems behind ipf and Speedstream 5861...
Date Sat, 09 Aug 2003 21:36:52 GMT
Can you FTP from the internet to a server on the local lan an transfer a meg or so file?

Like Robert said, I would hook Ethereal or your sniffer of choosing inbetween your DSL modem
the internal lan or inbetween your DSL modem and the Firewall if your running one. My first
would be that your suffering from MTU related issues. This can be either from the ISP end
or your
modem/router. If this is the case then the sniffer will see any ICMP error messages associated
when people from the internet are trying to pull up a normal html page.

Here's the link to ICMP types and codes:

Is your dsl modem PPPOE to the ISP or PPPOA?

One sure way of trouble shooting a PMTU or MTU issue is be using ping from an internal linux
unix machine to your default gateway modem and then up to the ISP.

What you do is set the size of a ping packet to 1472bytes and tell it not to fragement as
it goes
to its destination. You should be able to send a 1472bytes size packet out to the internt
with out
it getting fragemented. If it does get fragmented then start slowly lowering your ping packet
down until the packet is able to reach its destination. (goto the modems default gateway >isp<
then to

Here's an example of me doing this internally with 1472bytes tell then packet that not to
fragmented. So 1472bytes which with padding would be 1500. At a minimum you should be able
to get
away with a packet that big not getting fragmented.

[jbanks@localhost Desktop]$ ping -s 1472 -M do

PING ( from : 1472(1500) bytes of data.
1480 bytes from icmp_seq=1 ttl=128 time=0.747 ms
1480 bytes from icmp_seq=2 ttl=128 time=0.832 ms

Here's me pinging the same machine with a packet set to a packet size that is to large

[jbanks@localhost Desktop]$ ping -s 1473 -M do
PING ( from : 1473(1501) bytes of data.
ping: local error: Message too long, mtu=1500
ping: local error: Message too long, mtu=1500
ping: local error: Message too long, mtu=1500
ping: local error: Message too long, mtu=1500

This machine will not accept packet this packet size ( which most wont if they are bigger

This will send back a ICMP type 3 code 4. This might be what you see in you sniffer.

Joshua Banks

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