RE: ECN problem?

[Pawel Pilat <poster_pl@yahoo.com>]

--- "Mark E. Donaldson" <markee@bandwidthco.com>
wrote:
>  
> 
> -----Original Message-----
> From: netfilter-admin@lists.netfilter.org
> [mailto:netfilter-admin@lists.netfilter.org] On
> Behalf Of Pawel Pilat
> Sent: Tuesday, June 22, 2004 1:34 AM
> To: netfilter@lists.netfilter.org
> Subject: ECN problem?
> 
>  
> > -----Original Message-----
> > From: netfilter-admin@lists.netfilter.org
> > [mailto:netfilter-admin@lists.netfilter.org] On
> Behalf Of Pawel Pilat
> > Sent: Monday, June 21, 2004 1:59 AM
> > To: netfilter@lists.netfilter.org
> > Subject: ECN problem?
> > 
> > Hello everyone,
> > it's my first post on this list so plese
> understanding ...
> > I think that i have problem with ECN , this is my
> > situation:
> > 
> > IN--->R--->ISP
> > 
> > where:
> > IN - my internal net
> > R - my linux router (2.4.25, ipt-1.2.9) ISP - my
> ISP
> > 
> > so when i trying to connect from internal net to
> Internet i 
> > expirencing very slow transfers (500 - 700
> > bps) but from router everything is ok (transfer
> rate 50 - 60 kbps) 
> > when i used tcpdump on external interfece on
> router i realized that my 
> > ISP sends to me in every TCP packet TOS field set
> to 0x03 (ECN-CT
> > + ECN-CE) i think that
> > is the problem
> > 
> > i tried using:
> > 
> > iptables -t mangle -A PREROUTING -i $EXTIF -j TOS
> --set-tos 0x00 but 
> > without any result
> > 
> > my question is:
> > 1.it is possible to set linux box to ignore this
> fields in packets?
> > 2. there is another way to solve the problem?
> > 
> > thank for advices
> > best regards
> > 
> > POSTER PL
> > 
> > 
> > 
> > 		
> > __________________________________
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> > 
> > Most ISP have ECN enabled on their routers today,
> so this is not 
> > unusual. If the packets you are receiving from
> your ISP have
> > Cx=1 (0x03) then this means
> > it is indeed experiencing congestion, and if your
> box is also ECN 
> > enabled, then the congestion windows on both
> devices are probably 
> > being cut in half.
> > This needs to be confirmed before you do anything.
> > To confirm this, I would
> > suggest that you first check and see if you box is
> ECN enabled by 
> > checking your kernel config for CONFIG_INET_ECN=y.
> If it is, check the 
> > two high-order bits of bite 13 of the suspect TCP
> packet headers to 
> > see if the congestion windows are being cut. If
> so, then this is 
> > probably a correct assumption on your part. If so,
> the easiest 
> > solution would be to disable ECN on your box.
> > You would need to recompile the kernel to that of
> course. However, it 
> > would seem as though ECN is only doing its job and
> you may want to 
> > explore that avenue.
> > 
> > 
> > 
> >
>
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>
########################################################
> 
> Thnx Mark 
> 
> my box isn't ECN enabled for sure
> to be completly sure I issued: echo "0" >
> /proc/sys/net/ipv4/tcp_ecn
> 
> but this kind of behavior is strange for me or maybe
> my understanding of ECN
> isn't enough when i connect directly to ISP link non
> routing host everything
> seems to be OK (transfers rates) but EVERY returning
> packet in TCP sequence
> has TOS set to 0x03.
> 
> it seems that every packet in connection from my
> hosts makes ISP router
> congested - I don't think so - both interfaces of
> router are ethernet 100 i
> set MTU on external if to 1460 also tried with lower
> values and iptables
> ...... -j TCPMSS ... also without results 
> 
> so my theories :
> 
> 1. ISP sets TOS field to 0x03 on purpose on EVERY
> TCP packet directed to my
> host, but why?
> NAT preventing or sth ?
> 
> 2. bad ECN implementation ?
> it is possible but affects only those people who
> share their connection.
> at this point i must say that i dont want to make
> war with my ISP - i have 3
> PC and i want them all to be connected (network
> protocols and features test
> purposes)  generally it's not forbidden by ISP
> 
> i will examine those bytes just in case it's getting
> much interesting with
> each packet i captured ... :)  
> 
> i will be grateful for any advices
> 
> best regards
> POSTER PL
> 
>   
> 
>  This is indeed an interesting problem, and it
> sounds like you have been
> investigating it for a while. You mentioned that the
> TOS target was not
> effective. Why not try the -m tos match, and send
> the 0x03 TOS packets to
> the ECN target for processing? This target allows
> you to selectively work
> around known ECN blackholes: -j ECN
> --ecn-tcp-remove. Apply this in the
> mangle table with -p tcp. Just out of curiosity,
> what type of NICs are in
> your box? 
> 
> 
> 
>
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> This message has been scanned for viruses and
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> 
> postmaster@bandwidthco.com
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> protection.
>
########################################################
> 
> 
 
both are planet 8139 chipset based NICs so nothing
unusual
i totally forgot this netfilter target (ECN)! thnx for
that !
i will try it - i hope that it's what i needed

thnx

best regards 
POSTER PL


	
		
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