[rhos-list] Quantum: Packet Fragmentation Issue?

[Gary Kotton]

On 06/25/2013 08:54 PM, Johnray Fuller wrote:
> Hello,
>
>
> I appear to have an issue with packet fragmentation
>
> When we try to ssh from one VM to another where the VMs run on 
> different hosts on the source host the physical link (eth4) shows:
>
> 13:24:19.520812 fa:16:3e:dd:3c:4e (oui Unknown) > fa:16:3e:6c:eb:80 
> (oui Unknown), ethertype 802.1Q (0x8100), length 78: vlan 2, p 0, 
> ethertype IPv4, (tos 0x0, ttl 64, id 31721, offset 0, flags [DF], 
> proto TCP (6), length 60)
> 10.0.0.11.60025 > 10.0.0.12.ssh: Flags [S], cksum 0xdb91 (correct), 
> seq 3087184310, win 14600, options [mss 1460,sackOK,TS val 11061855 
> ecr 0,nop,wscale 6], length 0
>
> While on the receiving end we see:
>
> 13:24:20.555105 3e:6c:eb:80:fa:16 (oui Unknown) > 3c:4e:fa:16:fa:16 
> (oui Unknown), ethertype Unknown (0x3edd), length 78:
> 0x0000:  3c4e 0800 4500 003c 7be9 4000 4006 aabc <N..E..<{. at .@...
> 0x0010:  0a00 000b 0a00 000c ea79 0016 b802 b1b6  .........y......
> 0x0020:  0000 0000 a002 3908 db91 0000 0204 05b4  ......9.........
> 0x0030:  0402 080a 00a8 ca5f 0000 0000 0103 0306  ......._........
>

This looks like it could be related to VLAN splinters when using 
openvswitch. Are you using Openvswitch? Maybe 
http://git.openvswitch.org/cgi-bin/gitweb.cgi?p=openvswitch;a=blob_plain;f=FAQ;hb=HEADcan 
help.

Can you please past the NIC details. I have cc'ed Chris and Thomas.

Thanks
Gary

> It seems that encapsulation causes the packet to break. Does anyone 
> have any ideas on how to troubleshoot this?
>
> These VMs are on different hosts.
>
> We tried increasing the mtu on both hosts' eth4, but still no joy.
>
> We found the following, https://review.openstack.org/#/c/31518/ , 
> which might be related, but this patch was abandoned.
>
> Any assistance would be  greatly appreciated.
>
> J
>