Re: [Openstack-operators] MTU on router interface (neutron GRE) without jumbo
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. ___ OpenStack-operators mailing list OpenStack-operators@lists.openstack.org mailto:OpenStack-operators@lists.openstack.org http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-operators ___ OpenStack-operators mailing list OpenStack-operators@lists.openstack.org http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-operators
Re: [Openstack-operators] MTU on router interface (neutron GRE) without jumbo
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 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. ___ OpenStack-operators mailing list OpenStack-operators@lists.openstack.org http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-operators ___ OpenStack-operators mailing list OpenStack-operators@lists.openstack.org http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-operators
[Openstack-operators] MTU on router interface (neutron GRE) without jumbo
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. ___ OpenStack-operators mailing list OpenStack-operators@lists.openstack.org http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-operators
