Re: www.edirectory.co.uk -> TCP stack problem?

From: Christopher K. Johnson (ckjohnson_at_gwi.net)
Date: 09/29/04

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    Date: Wed, 29 Sep 2004 07:47:51 -0400
To: For users of Fedora Core releases <fedora-list@redhat.com>

    Douglas Furlong wrote:

    >Good morning All.
    >
    >I've recently noticed an odd problem with accessing www.edirectory.co.uk
    >
    >On all of my FC2 machines here, we recently stopped being able to access
    >the above site. Via Firefox, Mozilla, elinks. All of them fail saying
    >document contains no data.
    >
    >I have used tcpdump host www.edirectory.co.uk both on the client and
    >firewall to try and get a better idea of what is going on, and I used
    >ethereal on the client. Below is what I get.
    >
    >Firewall
    >--------
    >11:11:27.584098 192.168.0.181.34506 > www.edirectory.co.uk.http: S
    >1062279754:1062279754(0) win 5840 <mss 1460,sackOK,timestamp 62570253
    >0,nop,wscale 7> (DF)
    >11:11:27.605934 www.edirectory.co.uk.http > 192.168.0.181.34506: S
    >4164346285:4164346285(0) ack 1062279755 win 17520 <mss 1460,nop,wscale
    >0,nop,nop,timestamp 0 0,nop,nop,sackOK> (DF)
    >11:11:27.606108 192.168.0.181.34506 > www.edirectory.co.uk.http: . ack 1
    >win 46 <nop,nop,timestamp 62570275 0> (DF)
    >11:11:27.606482 192.168.0.181.34506 > www.edirectory.co.uk.http: P 1:452
    >(451) ack 1 win 46 <nop,nop,timestamp 62570275 0> (DF)
    >11:11:27.828597 192.168.0.181.34506 > www.edirectory.co.uk.http: P 1:452
    >(451) ack 1 win 46 <nop,nop,timestamp 62570497 0> (DF)
    >11:11:27.864180 www.edirectory.co.uk.http > 192.168.0.181.34506: . ack
    >452 win 17069 <nop,nop,timestamp 11171953 62570497> (DF)
    >
    >Client
    >------
    >11:03:33.441591 IP 192.168.0.181.34506 > www.edirectory.co.uk.http: S
    >1062279754:1062279754(0) win 5840 <mss 1460,sackOK,timestamp 62570253
    >0,nop,wscale 7>
    >11:03:33.463543 IP www.edirectory.co.uk.http > 192.168.0.181.34506: S
    >4164346285:4164346285(0) ack 1062279755 win 17520 <mss 1460,nop,wscale
    >0,nop,nop,timestamp 0 0,nop,nop,sackOK>
    >11:03:33.463604 IP 192.168.0.181.34506 > www.edirectory.co.uk.http: .
    >ack 1 win 46 <nop,nop,timestamp 62570275 0>
    >11:03:33.463836 IP 192.168.0.181.34506 > www.edirectory.co.uk.http: P
    >1:452(451) ack 1 win 46 <nop,nop,timestamp 62570275 0>
    >11:03:33.684898 IP 192.168.0.181.34506 > www.edirectory.co.uk.http: P
    >1:452(451) ack 1 win 46 <nop,nop,timestamp 62570497 0>
    >11:03:33.721780 IP www.edirectory.co.uk.http > 192.168.0.181.34506: .
    >ack 452 win 17069 <nop,nop,timestamp 11171953 62570497>
    >
    >Ethereal Output (attached).
    >
    >I am currently running kernel 2.6.8-1.521
    >
    >We have tested access to the site on both windows and FC1 fully updated
    >and the site comes up fine.
    >
    >The ethereal output seems to suggest that it feels the TCP sequence is
    >"wrong", and the two tcpdump outputs heavily suggest there is a problem
    >on our end.
    >
    >So far I have tried the following kernels, which allow me to access the
    >site.
    >2.6.5-1.358
    >2.6.6-1.427
    >2.6.6-1.435
    >2.6.6-1.435.2.1
    >2.6.6-1.435.2.3
    >2.6.8-1.541
    >
    >So far I have tried the following kernels, which do NOT allow me to
    >access the site.
    >2.6.7-1.494.2.2
    >2.6.8-1.521
    >
    >
    >
    I see that window scaling is involved. Try adding the following two
    entries, to /etc/sysctl.conf (2nd one for wscale):
    -------- Start /etc/sysctl.conf additions ------
    # Disable TCP ECN which some routers and servers cannot handle.
    net.ipv4.tcp_ecn = 0
     
    # Disable TCP window scaling which some routers and firewalls cannot handle.
    net.ipv4.tcp_window_scaling = 0
    -------- End /etc/sysctl.conf additions ------
     
    Then activate the change:
    sysctl -p

    Chris 

    -- 
-----------------------------------------------------------
   "Spend less!  Do more!  Go Open Source..." -- Dirigo.net
   Chris Johnson, RHCE #807000448202021
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