Ubuntu: eoan
DPDK pkg: 18.11.1-3
OVS DPDK pkg: 2.11.0-0ubuntu2
Kerenl: 5.0.0-20-generic

If a server has an ovs bridge with a dpdk device for external
network access and a network namespace attached then sending data out of
the namespace fails if jumbo frames are enabled. 

Setup:

root@node-licetus:~# uname -r
5.0.0-20-generic

root@node-licetus:~# ovs-vsctl show
523eab62-8d03-4445-a7ba-7570f5027ff6
    Bridge br-test
        Port "tap1"
            Interface "tap1"
                type: internal
        Port br-test
            Interface br-test
                type: internal
        Port "dpdk-nic1"
            Interface "dpdk-nic1"
                type: dpdk
                options: {dpdk-devargs="0000:03:00.0"}
    ovs_version: "2.11.0"

root@node-licetus:~# ovs-vsctl get Interface dpdk-nic1 mtu
9000

root@node-licetus:~# ip netns exec ns1 ip addr show tap1
12: tap1: <BROADCAST,MULTICAST,PROMISC,UP,LOWER_UP> mtu 9000 qdisc fq_codel state UNKNOWN group default qlen 1000
    link/ether 0a:dd:76:38:52:54 brd ff:ff:ff:ff:ff:ff
    inet 10.246.112.101/21 scope global tap1
       valid_lft forever preferred_lft forever
    inet6 fe80::8dd:76ff:fe38:5254/64 scope link 
       valid_lft forever preferred_lft forever


* Using iperf to send data out of the netns fails:

root@node-licetus:~# ip netns exec ns1 iperf -c 10.246.114.29
------------------------------------------------------------
Client connecting to 10.246.114.29, TCP port 5001
TCP window size:  325 KByte (default)
------------------------------------------------------------
[  3] local 10.246.112.101 port 51590 connected with 10.246.114.29 port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.3 sec   323 KBytes   257 Kbits/sec

root@node-hippalus:~# iperf -s -m
------------------------------------------------------------
Server listening on TCP port 5001
TCP window size:  128 KByte (default)
------------------------------------------------------------
root@node-hippalus:~# 

* Switching the direction of flow and sending data into the namespace works:

root@node-licetus:~# ip netns exec ns1 iperf -s -m
------------------------------------------------------------
Server listening on TCP port 5001
TCP window size:  128 KByte (default)
------------------------------------------------------------
[  4] local 10.246.112.101 port 5001 connected with 10.246.114.29 port 59454
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-10.0 sec  6.06 GBytes  5.20 Gbits/sec
[  4] MSS size 8948 bytes (MTU 8988 bytes, unknown interface)

root@node-hippalus:~# iperf -c 10.246.112.101
------------------------------------------------------------
Client connecting to 10.246.112.101, TCP port 5001
TCP window size:  942 KByte (default)
------------------------------------------------------------
[  3] local 10.246.114.29 port 59454 connected with 10.246.112.101 port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec  6.06 GBytes  5.20 Gbits/sec

* Using iperf to send data out of the netns after dropping tap mtu works:


root@node-licetus:~# ip netns exec ns1 ip link set dev tap1 mtu 1500
root@node-licetus:~# ip netns exec ns1 iperf -c 10.246.114.29
------------------------------------------------------------
Client connecting to 10.246.114.29, TCP port 5001
TCP window size:  845 KByte (default)
------------------------------------------------------------
[  3] local 10.246.112.101 port 51594 connected with 10.246.114.29 port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec   508 MBytes   426 Mbits/sec

root@node-hippalus:~# iperf -s -m
------------------------------------------------------------
Server listening on TCP port 5001
TCP window size:  128 KByte (default)
------------------------------------------------------------
[  4] local 10.246.114.29 port 5001 connected with 10.246.112.101 port 51594
[ ID] Interval       Transfer     Bandwidth
[  4]  0.0-10.1 sec   508 MBytes   424 Mbits/sec
[  4] MSS size 1448 bytes (MTU 1500 bytes, ethernet)