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[Bug 1443607] Re: Linux Bridge: can't change the VM's bridge and tap interface MTU at Compute node.

 

** Also affects: neutron
   Importance: Undecided
       Status: New

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https://bugs.launchpad.net/bugs/1443607

Title:
  Linux Bridge: can't change the VM's bridge and tap interface MTU at
  Compute node.

Status in Cisco Vendor Code for OpenStack Neutron:
  New
Status in OpenStack Neutron (virtual network service):
  New

Bug description:
  I use DevStack to deploy OpenStack with Linux Bridge instead of OVS in
  a multi-node set up.

  I¹m testing jumbo frames and want to set MTU to 9000.

  At the Network node, the bridges and tap interfaces are created with
  MTU = 9000:

  localadmin@qa4:~/devstack$ brctl show
  bridge name           bridge id                     STP enabled   interfaces
  brq09047ecb-1c   8000.7c69f62c4f2f   no                      eth1
                                                                                                        tapedbcd5b1-a6
  brq319688ab-93   8000.3234d6ee3a18  no                   bond0.300
                                                                                                        tap4e230a86-cb
                                                                                                        tapfddaf12e-85
  virbr0                        8000.000000000000  yes

  localadmin@qa4:~/devstack$ ifconfig brq09047ecb-1c
  brq09047ecb-1c Link encap:Ethernet  HWaddr 7c:69:f6:2c:4f:2f
            inet6 addr: fe80::3c79:c8ff:fe23:2fe7/64 Scope:Link
            UP BROADCAST RUNNING MULTICAST  MTU:9000  Metric:1
            RX packets:696 errors:0 dropped:0 overruns:0 frame:0
            TX packets:8 errors:0 dropped:0 overruns:0 carrier:0
            collisions:0 txqueuelen:0
            RX bytes:30617 (30.6 KB)  TX bytes:648 (648.0 B)

  localadmin@qa4:~/devstack$ ifconfig brq319688ab-93
  brq319688ab-93 Link encap:Ethernet  HWaddr 32:34:d6:ee:3a:18
            inet6 addr: fe80::e0ec:3bff:fe09:4318/64 Scope:Link
            UP BROADCAST RUNNING MULTICAST  MTU:9000  Metric:1
            RX packets:30 errors:0 dropped:0 overruns:0 frame:0
            TX packets:8 errors:0 dropped:0 overruns:0 carrier:0
            collisions:0 txqueuelen:0
            RX bytes:4236 (4.2 KB)  TX bytes:648 (648.0 B)

  localadmin@qa4:~/devstack$ ifconfig tapedbcd5b1-a6
  tapedbcd5b1-a6 Link encap:Ethernet  HWaddr ae:fb:64:53:f7:2d
            inet6 addr: fe80::acfb:64ff:fe53:f72d/64 Scope:Link
            UP BROADCAST RUNNING MULTICAST  MTU:9000  Metric:1
            RX packets:65 errors:0 dropped:0 overruns:0 frame:0
            TX packets:947 errors:0 dropped:0 overruns:0 carrier:0
            collisions:0 txqueuelen:1000
            RX bytes:10223 (10.2 KB)  TX bytes:80510 (80.5 KB)

  localadmin@qa4:~/devstack$ ifconfig tap4e230a86-cb
  tap4e230a86-cb Link encap:Ethernet  HWaddr 32:34:d6:ee:3a:18
            inet6 addr: fe80::3034:d6ff:feee:3a18/64 Scope:Link
            UP BROADCAST RUNNING MULTICAST  MTU:9000  Metric:1
            RX packets:2073 errors:0 dropped:0 overruns:0 frame:0
            TX packets:2229 errors:0 dropped:0 overruns:0 carrier:0
            collisions:0 txqueuelen:1000
            RX bytes:8878139 (8.8 MB)  TX bytes:8914532 (8.9 MB)

  localadmin@qa4:~/devstack$ ifconfig tapfddaf12e-85
  tapfddaf12e-85 Link encap:Ethernet  HWaddr d2:33:29:9b:2c:e8
            inet6 addr: fe80::d033:29ff:fe9b:2ce8/64 Scope:Link
            UP BROADCAST RUNNING MULTICAST  MTU:9000  Metric:1
            RX packets:152 errors:0 dropped:0 overruns:0 frame:0
            TX packets:295 errors:0 dropped:0 overruns:0 carrier:0
            collisions:0 txqueuelen:1000
            RX bytes:15237 (15.2 KB)  TX bytes:51849 (51.8 KB)


  The instance launched at the Compute node has interface eth0 MTU =
  9000:

  ubuntu@qa5-vm2:~$ ifconfig
  eth0      Link encap:Ethernet  HWaddr fa:16:3e:05:36:58
            inet addr:10.0.0.4  Bcast:10.0.0.255  Mask:255.255.255.0
            inet6 addr: fe80::f816:3eff:fe05:3658/64 Scope:Link
            UP BROADCAST RUNNING MULTICAST  MTU:9000  Metric:1
            RX packets:1169 errors:0 dropped:0 overruns:0 frame:0
            TX packets:384 errors:0 dropped:0 overruns:0 carrier:0
            collisions:0 txqueuelen:1000
            RX bytes:1408206 (1.4 MB)  TX bytes:1336535 (1.3 MB)

  
  However, the associated bridge and tap interface MTU is set to default 1500:

  localadmin@qa5:~/devstack$ brctl show
  bridge name           bridge id                         STP enabled   interfaces
  brq319688ab-93   8000.6805ca302558   no                       bond0.300
                                                                                                            tapa7acee8a-54
  virbr08000.000000000000  yes

  localadmin@qa5:~/devstack$ ifconfig brq319688ab-93
  brq319688ab-93 Link encap:Ethernet  HWaddr 68:05:ca:30:25:58
            inet6 addr: fe80::a8ef:dfff:feb1:8eec/64 Scope:Link
            UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
            RX packets:162 errors:0 dropped:0 overruns:0 frame:0
            TX packets:8 errors:0 dropped:0 overruns:0 carrier:0
            collisions:0 txqueuelen:0
            RX bytes:910353 (910.3 KB)  TX bytes:648 (648.0 B)

  localadmin@qa5:~/devstack$ ifconfig tapa7acee8a-54
  tapa7acee8a-54 Link encap:Ethernet  HWaddr fe:16:3e:05:36:58
            inet6 addr: fe80::fc16:3eff:fe05:3658/64 Scope:Link
            UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
            RX packets:395 errors:0 dropped:0 overruns:0 frame:0
            TX packets:1180 errors:0 dropped:0 overruns:0 carrier:0
            collisions:0 txqueuelen:500
            RX bytes:1338757 (1.3 MB)  TX bytes:1408932 (1.4 MB)

  localadmin@qa5:~/devstack$ ifconfig bond0.300
  bond0.300 Link encap:Ethernet  HWaddr 68:05:ca:30:25:58
            inet6 addr: fe80::6a05:caff:fe30:2558/64 Scope:Link
            UP BROADCAST RUNNING MULTICAST  MTU:9000  Metric:1
            RX packets:11507 errors:0 dropped:0 overruns:0 frame:0
            TX packets:11590 errors:0 dropped:0 overruns:0 carrier:0
            collisions:0 txqueuelen:0
            RX bytes:14831272 (14.8 MB)  TX bytes:14943870 (14.9 MB)

  
  As a result, jumbo frames are fragmented coming out from the Compute node.

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