wget on an OpenStack instance hangs ? Try lowering the MTU

Why would OpenStack instances fail to wget a URL and work perfectly on others ? For instance:

$ wget -O - 'https://ceph.com/git/?p=ceph.git;a=blob_plain;f=keys/autobuild.asc'
Connecting to ceph.com (ceph.com)|208.113.241.137|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: unspecified [text/plain]
Saving to: `STDOUT'

    [< =>                                                                           ] 0           --.-K/s              ^

If it can be fixed by lowering the MTU from the default of 1500 to 1400 with:

$ sudo ip link set mtu 1400 dev eth0
$ sudo ip link show dev eth0
2: eth0:  mtu 1400 qdisc pfifo_fast state UP qlen 1000
    link/ether fa:16:3e:85:ee:a5 brd ff:ff:ff:ff:ff:ff

it means the underlying OpenStack DHCP should be fixed to set the MTU to 1400.
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tinc based L2 mesh for OpenStack

Given three bare metal machines hosted at Hetzner, eNovance and OVH, l2mesh can be used to create a new ethernet interface L2M on each of them. It behaves as if they had a physical ethernet card connected to a hardware switch in the same room. The machine at eNovance could be the DHCP server providing the IP for the L2M interface of the Hetzner machine. In addition, if the connection between the eNovance machine and the Hetzner machine does not work, the packets will use the OVH machine as an intermediary, making the mesh resilient to network outage.
The documentation page for l2mesh has been added to the example section of the tinc web site after a discussion with Guus Sliepen.
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