[lvs-users] LVS problem with unreachable - need to frag
khapare77 at gmail.com
Fri Mar 9 16:30:14 GMT 2012
could it be due to i install on virtual server which mean network interface
is shared - is that could be a bottleneck ? I am not sure how to debug this
On Thu, Mar 8, 2012 at 7:05 PM, Khapare Joshi <khapare77 at gmail.com> wrote:
> Thanks for your quick response.
> On Thu, Mar 8, 2012 at 5:33 PM, Michael Schwartzkopff <
> misch at schwartzkopff.org> wrote:
>> > Hello all,
>> > I am running pulse on virtual machine for webserver, it seems working
>> > well, but there is one problem with networking I think. It seems there
>> > is a problem with lvs server is not fragmenting larger than 1500
>> > packets size. I did the quick tcpdump and I get following info.
>> > my problem is when user is uploading files it takes for ever and never
>> > completes. I am thinking lvs (pulse) is not not fragmenting the larger
>> > packet size than 1500 hence it never goes to backend server.
>> > 16:25:22.543563 00:1f:6d:cf:4e:49 > 52:54:00:b5:30:3c, ethertype IPv4
>> > (0x0800), length 2974: 10.128.1.5.60715 > 10.192.6.1.https: Flags [.],
>> > seq 7705:10625, ack 146, win 16388, length 2920
>> > 16:25:22.543590 52:54:00:b5:30:3c > 00:1f:6d:cf:4e:49, ethertype IPv4
>> > (0x0800), length 590: 10.192.6.1 > 10.128.1.5: ICMP 18.104.22.168
>> > unreachable - need to frag (mtu 1500), length 556
>> > I tested following:
>> > 1. IP forward is enabled.
>> > 2. lro,gro are off on eth0
>> > ethtool -k eth0
>> > Offload parameters for eth0:
>> > rx-checksumming: on
>> > tx-checksumming: on
>> > scatter-gather: on
>> > tcp-segmentation-offload: on
>> > udp-fragmentation-offload: on
>> > generic-segmentation-offload: on
>> > generic-receive-offload: off
>> > large-receive-offload: off
>> > 3. IPVS version is v1.2.1
>> > 4. Backend server has arptables and set to mangaled to right interface
>> > 5. Firewall is allowed on both lvs and backend server.
>> > 6. http and https are open for all.
>> > Any help in this would be great.
>> It seems that the LVS cannot send out the packet since the MTU is too
>> for the 1500 Byte of the interface. Please don't be confused by the
>> length of
>> 2974 byte that tcpdump shows. tcpdump just sees the packet on the wrong
>> on the chain.
>> I see, how tcpdump reference length 2974 byte ? I was trying to
> understand this length and concluded it is something problem with lvs.
>> Be sure the Path MTU discovery works or clear the DF bit of the packet
>> entering the load balancer.
>> how do I check this, or is there a way to tell lvs to if the packet size
> is larger then force to defrag ? Perhaps this should be handed in linux
> kernel ? I am using redhat 6.2
>> Dr. Michael Schwartzkopff
>> Guardinistr. 63
>> 81375 München
>> Tel: (0163) 172 50 98
>> Fax: (089) 620 304 13
>> Please read the documentation before posting - it's available at:
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