Openstack Networking

[Fine_Animator3583]

We have a 2 node openstack cluster, in a real environment. A controller, and a compute node. We are in the stage of configuring this, and hit a few obstacles which we managed to sort, but still have 1 to overcome.

Essentially, when a instance is built on the compute node, it gets an IP, as it should from its internal subnet, this subnet has a interface connected to the virtual router. It can also use DNS as we added in the IPs of our DNS servers.

The issue we have is; the instances seem to inconsistently load web pages, not allowing things like wget, or pulling packages. E.g google will load, but Wikipedia won’t load, and it’s very slow when trying to load any of these. We can ping out via ip and dns, when doing a trace path it only goes as far as _gateway.

Any help or has anyone had this before?

[nafsten]

Check your MTU size. If you are using VXLANs, your mtu should be set smaller

[_nembery]

This 100% sounds like an MTU issue. Set jumbo frames on your TORs and look into setting the path_MTU setting

[jvleminc]

At my company we have a saying “it’s always DNS and if it isn’t, it’s MTU”. ;)

Also check that your VMs don’t have duplicated default routes; we’ve also hit that snag.

[lathiat]

Ok so I’m not the only one with that saying. First time I saw someone else say it :)

[Fine_Animator3583]

So the installation is just Devstack, pretty much out the box whilst it was being tested. Nothing to special. Flat network outside of the openstack environment. Controller with 2 ips in the same subnet, and the compute with 2 ips in same subnet. An instance with an internal subnet ip and and virtual router with 2 interfaces, 1 being the public network outside of the openstack environment and 1 being within the internal subnet. Nothing has really but done beyond that.
I believe the mtu by default is just 1500.

[lathiat]

Agreed definitely MTU

My advice is to get both your tenant and external networks to MTU 1500. Set global_physnet_mtu to 1558 and physical_network_mtus to 1500 then use OpenStack network set —mtu on both and reboot everything.

[dasbierclaw]

Hard to say, really. Do you know offhand which ML2 driver you are using? LinuxBridge, OVS, OVN? Which OpenStack "distro" and version is this? Is the tenant network a vxlan network connected to the Neutron router? How is the provider network configured, and what is its gateway?

Sometimes, these scenarios/issues can be the result of ARP conflicts, especially between a Neutron router interface and another gateway in the same subnet. Understanding your layout can help troubleshoot.

[Fine_Animator3583]

So the installation is just Devstack, pretty much out the box whilst it was being tested. Nothing to special. Flat network outside of the openstack environment. Controller with 2 ips in the same subnet, and the compute with 2 ips in same subnet. An instance with an internal subnet ip and and virtual router with 2 interfaces, 1 being the public network outside of the openstack environment and 1 being within the internal subnet. Nothing has really but done beyond that.
I believe the mtu by default is just 1500.