Thanks!
But those examples are for same MTU for client and server. If we have
Client: 1500
router in the middle 1500
OVS/GRE: 1458
server: 1458
For tcp this is ok. But can it hurt somehow other protocols? UDP, RST, etc?
On 03/14/2015 08:52 PM, Joseph Bajin wrote:
The size of MTU only really matters for the server and client. The
between connections need to be larger than the packets that are being
sent.
Scenario 1:
Server - 1400 MTU
Client - 1400 MTU
Switches - 9216 MTU
OVS - 1500 MTU
Result: Successful - Traffic passes without any issue
Scenario 2:
Server - 1520 MTU
Client - 1520 MTU
Switches - 1516 MTU
OVS - 1500 MTU
Result: Failure - Traffic will have issues passing through.
So just make sure everything in-between is higher than your server and
client.
--Joe
On Fri, Mar 13, 2015 at 9:28 AM, George Shuklin
<george.shuk...@gmail.com <mailto:george.shuk...@gmail.com>> wrote:
Hello.
We've hit badly changes in behaviour of OVS when we switched from
3.08 to 3.13 kernel. When runs on 3.11 or above, OVS starts to
use kernel GRE services. And they copy DNF (do not fragment) flag
from encapsulated packet to GRE packet. And this mess up all
things, because ICMP messages about dropped GRE never reach
neither source nor destination of underlying TCP.
We've fixed problems with MTU by using option for DHCP for
dnsmasq. This lower MTU inside instances. But there are routers
(router namespaces) and they are still using 1500 bytes MTU.
I feel like this can cause problems with some types of traffic,
when client (outside of openstack) sending DNF packets to instance
(via floating) and that packet is silently dropped.
1) Is those concerns have any real life implication? TCP should
take in account MTU on server and works smoothly, but other protocols?
2) Is there any way to lower MTU inside router namespace?
Thanks.
P.S. Jumbo frames is not an option due reasons outside of our reach.
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