On Wed, January 29, 2014 01:11, Thomas Glanzmann wrote:
> In order to avoide the problem you either have to lower the MTU in the
> VMs which you did or you enable bigger packets in your transport
> network. This is called jumbo frames. On HP procurve switches they're
> enabled by saying
A particular detail: on which host (i.e, non-VM) interfaces does one
change the MTU for OpenStack? For example, on OS compute nodes, there is
the actual NIC (eth0), but also br-int and br-tun (where the GRE tunnels
connect to):
$ ifconfig
br-int Link encap:Ethernet HWaddr 32:fc:21:25:7b:41
inet6 addr: fe80::30e6:33ff:fe66:402/64 Scope:Link
UP BROADCAST RUNNING MTU:1500 Metric:1
br-tun Link encap:Ethernet HWaddr 82:bc:cc:56:76:4f
inet6 addr: fe80::aca4:f3ff:fef9:e193/64 Scope:Link
UP BROADCAST RUNNING MTU:1500 Metric:1
eth0 Link encap:Ethernet HWaddr aa:bb:0b:dd:af:72
inet addr:10.0.20.60 Bcast:10.0.20.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
Then there are a bunch of tap, qbr, qvb, and qvo interfaces. Would the MTU
change be on just eth0, or br-tun as well?
Then on the OS network node, we have eth0, br-tun (GRE end-point), and
br-ex. (Ideally there would be an eth1 for the back-end "data network",
but our beta infrastructure hardware only has eth0.)
br-ex Link encap:Ethernet HWaddr 00:1e:0b:bc:09:c4
inet addr:10.0.20.77 Bcast:10.0.20.255 Mask:255.255.255.0
inet6 addr: fe80::50de:9dff:fee5:103d/64 Scope:Link
UP BROADCAST RUNNING MTU:1500 Metric:1
br-int Link encap:Ethernet HWaddr 32:95:87:9b:2b:49
inet6 addr: fe80::7036:73ff:fefb:6a30/64 Scope:Link
UP BROADCAST RUNNING MTU:1500 Metric:1
br-tun Link encap:Ethernet HWaddr ae:ab:60:d2:75:4c
inet6 addr: fe80::a08d:fff:fed7:b283/64 Scope:Link
UP BROADCAST RUNNING MTU:1500 Metric:1
eth0 Link encap:Ethernet HWaddr aa:bb:0b:dd:09:ef
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
So should larger / jumbo frames be enabled on br-tun (for GRE) and on eth0
(because GRE travels over it; on eth1 if we had an independent back-end
data network).
We can leave the MTU on br-ex as 1500 if we want, because there shouldn't
any encapsulated traffic running over it. (Though jumbo frames wouldn't
hurt.)
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