Re: [openstack-dev] [neutron] VXLAN with single-NIC compute nodes: Avoiding the MTU pitfalls

2015-03-13 Thread Ian Wells
On 12 March 2015 at 05:33, Fredy Neeser fredy.nee...@solnet.ch wrote:

  2.  I'm using policy routing on my hosts to steer VXLAN traffic (UDP
 dest. port 4789) to interface br-ex.12 --  all other traffic from
 192.168.1.14 is source routed from br-ex.1, presumably because br-ex.1 is a
 lower-numbered interface than br-ex.12  (?) -- interesting question whether
 I'm relying here on the order in which I created these two interfaces.


OK, I have to admit I've never used policy routing in anger so I can't
speak with much confidence here.  I wonder if anything (link down, for
instance) might cause Linux to change its preference behaviour, though, and
your to-the-world packets haven't got a policy from what you say so a
preference change would be a disaster.

3.  It's not clear to me how to setup multiple nodes with packstack if a
 node's tunnel IP does not equal its admin IP (or the OpenStack API IP in
 case of a controller node).  With packstack, I can only specify the compute
 node IPs through CONFIG_COMPUTE_HOSTS.  Presumably, these IPs are used for
 both packstack deployment (admin IP) and for configuring the VXLAN tunnel
 IPs (local_ip and remote_ip parameters).  How would I specify different IPs
 for these purposes?  (Recall that my hosts have a single NIC).


I don't think the single NIC is an issue, particularly, and even less so if
you have multiple interfaces, even VLAN interfaces, with different
addresses.  At that point you should be able to use
CONFIG_NEUTRON_OVS_TUNNEL_IF=eth1.12 , which would need to be created and
addressed by the point you run packstack, as it expects it to be there at
this point.  In fact the closed bug
https://bugs.launchpad.net/packstack/+bug/1279517 suggests that you're not
the first to try this and it does work (though since the change it refers
to isn't merged you might need to say ...=eth1_12 to keep packstack happy).

You may find that configuring a VLAN interface for eth1.12 (not in a
 bridge, with a local address suitable for communication with compute nodes,
 for VXLAN traffic) and eth1.1 (in br-ex, for external traffic to use) does
 better for you.

   Hmm, I only have one NIC (eth0).


Apparently I can't read - where I'm putting eth1 I mean eth0 in your setup,
I must have misread it early on.   I'll try and make the switch.

eth0.1 is shorthand notation for eth0 VLAN 1, and there are a bunch of
interface management commands to create interfaces of this type. It appears
to be possible to configure this in the network setup scripts -
https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/Networking_Guide/sec-Configure_802_1Q_VLAN_Tagging_Using_the_Command_Line.html
describes the Redhat way, though I've only done this on Ubuntu and Debian
myself.

In order to attach eth0 to br-ex, I had to configure it as an OVSPort.
 Maybe I misunderstand your alternative, but are you suggesting  to
 configure  eth0.1 as an OVSPort (connected to br-ex), and  eth0.12 as a
 standalone interface?  (Not sure a physical interface can be brain split
 in such a way.)


eth0.1 is a full on network interface and should work as an OVS port.  You
would configure the external network in Openstack as flat, rather than
containing VLAN segments, because the tagging is done outside of Openstack
with this approach (otherwise you'd end up with double tagged packets).

And yes, eth0.12 would be a standalone interface.

Note that my physical switch uses a native VLAN of 1  and is configured
 with Untag all ports for VLAN 1. Moreover, OVSPort eth0 (attached to
 br-ex) is configured for VLAN trunking with a native VLAN of 1 (vlan_mode:
 native-untagged, trunks: [1,12], tag: 1), so within bridge br-ex, native
 packets are tagged 1.


Yes, as I say, if you moved over to the eth0.1 mechanism above you'd want
the packets to be untagged at the eth0.1 OVS port, because receiving them
via eth0.1 would untag them (and sending them would tag them) and OVS
doesn't need to help you out on the VLAN front any more.

I'm still not a fan of your setup but I don't know if it's just because
it's not where my natural preference lies.  You may be inches from making
it work perfectly, and I'm not sure I would be able to tell.  That said,
policy routing seems like a workaround to a problem you're having with
packstack; I would definitely go with two addresses if there were any way
to make it configure properly.  If I were doing this there would also be
quite a lot of experimentation to verify my guesswork, I have to admit, so
it's not an easy answer.
-- 
Ian.
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Re: [openstack-dev] [neutron] VXLAN with single-NIC compute nodes: Avoiding the MTU pitfalls

2015-03-12 Thread Fredy Neeser


On 11.03.2015 19:31, Ian Wells wrote:
On 11 March 2015 at 04:27, Fredy Neeser fredy.nee...@solnet.ch 
mailto:fredy.nee...@solnet.ch wrote:


7: br-ex.1: BROADCAST,MULTICAST,UP,LOWER_UP mtu 1500 qdisc
noqueue state UNKNOWN group default
link/ether e0:3f:49:b4:7c:a7 brd ff:ff:ff:ff:ff:ff
inet 192.168.1.14/24 http://192.168.1.14/24 brd
192.168.1.255 scope global br-ex.1
   valid_lft forever preferred_lft forever

8: br-ex.12: BROADCAST,MULTICAST,UP,LOWER_UP mtu 1554 qdisc
noqueue state UNKNOWN group default
link/ether e0:3f:49:b4:7c:a7 brd ff:ff:ff:ff:ff:ff
inet 192.168.1.14/24 http://192.168.1.14/24 brd
192.168.1.255 scope global br-ex.12
   valid_lft forever preferred_lft forever


I find it hard to believe that you want the same address configured on 
*both* of these interfaces - which one do you think will be sending 
packets?


Ian, thanks for your feedback!

I did choose the same address for the two interfaces, for three reasons:

1.  Within my home single-LAN (underlay) environment, traffic is 
switched, and VXLAN traffic is confined to VLAN 12, so there is never a 
conflict between IP 192.168.1.14 on VLAN 1 and the same IP on VLAN 12.
OTOH, for a more scalable VXLAN setup (with multiple underlays and L3 
routing in between), I would like to use different IPs for br-ex.1 and 
br-ex.12 -- for example by using separate subnets

  192.168.1.0/26  for VLAN 1
  192.168.12.0/26  for VLAN 12
However, I'm not quite there yet (see 3.).

2.  I'm using policy routing on my hosts to steer VXLAN traffic (UDP 
dest. port 4789) to interface br-ex.12 --  all other traffic from 
192.168.1.14 is source routed from br-ex.1, presumably because br-ex.1 
is a lower-numbered interface than br-ex.12  (?) -- interesting question 
whether I'm relying here on the order in which I created these two 
interfaces.


  [root@langrain ~]# ip a
  ...
  7: br-ex.1: BROADCAST,MULTICAST,UP,LOWER_UP mtu 1500 qdisc noqueue 
state UNKNOWN group default

  link/ether e0:3f:49:b4:7c:a7 brd ff:ff:ff:ff:ff:ff
  inet 192.168.1.14/24 brd 192.168.1.255 scope global br-ex.1
 valid_lft forever preferred_lft forever
  8: br-ex.12: BROADCAST,MULTICAST,UP,LOWER_UP mtu 1554 qdisc noqueue 
state UNKNOWN group default

  link/ether e0:3f:49:b4:7c:a7 brd ff:ff:ff:ff:ff:ff
  inet 192.168.1.14/24 brd 192.168.1.255 scope global br-ex.12
 valid_lft forever preferred_lft forever

3.  It's not clear to me how to setup multiple nodes with packstack if a 
node's tunnel IP does not equal its admin IP (or the OpenStack API IP in 
case of a controller node).  With packstack, I can only specify the 
compute node IPs through CONFIG_COMPUTE_HOSTS. Presumably, these IPs are 
used for both packstack deployment (admin IP) and for configuring the 
VXLAN tunnel IPs (local_ip and remote_ip parameters).  How would I 
specify different IPs for these purposes? (Recall that my hosts have a 
single NIC).



In any case, native traffic on bridge br-ex is sent via br-ex.1 (VLAN 
1), which is also the reason the Neutron gateway port qg-XXX needs to be 
an access port for VLAN 1 (tag: 1).   VXLAN traffic is sent from 
br-ex.12 on all compute nodes.  See the 2 cases below:



Case 1. Max-size ping from compute node 'langrain' (192.168.1.14) to 
another host on same LAN
 = Native traffic sent from br-ex.1; no traffic sent from 
br-ex.12


[fn@langrain ~]$ ping -M do -s 1472 -c 1 192.168.1.54
PING 192.168.1.54 (192.168.1.54) 1472(1500) bytes of data.
1480 bytes from 192.168.1.54: icmp_seq=1 ttl=64 time=0.766 ms

[root@langrain ~]# tcpdump -n -i br-ex.1 dst 192.168.1.54
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on br-ex.1, link-type EN10MB (Ethernet), capture size 65535 bytes
10:32:37.666572 IP 192.168.1.14  192.168.1.54: ICMP echo request, id 
10432, seq 1, length 1480
10:32:42.673665 ARP, Request who-has 192.168.1.54 tell 192.168.1.14, 
length 28



Case 2: Max-size ping from a guest1 (10.0.0.1) on compute node 
'langrain' (192.168.1.14)
 to a guest2 (10.0.0.3) on another compute node 
(192.168.1.21) via VXLAN tunnel.

 Guests are on the same virtual network 10.0.0.0/24
 = Encapsulated traffic sent from br-ex.12; no traffic 
sent from br-ex.1


$ ping -M do -s 1472 -c 1 10.0.0.3
PING 10.0.0.3 (10.0.0.3) 1472(1500) bytes of data.
1480 bytes from 10.0.0.3: icmp_seq=1 ttl=64 time=2.22 ms

[root@langrain ~]# tcpdump -n -i br-ex.12
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on br-ex.12, link-type EN10MB (Ethernet), capture size 65535 bytes

11:02:56.916265 IP 192.168.1.14.47872  192.168.1.21.4789: VXLAN, flags 
[I] (0x08), vni 10

ARP, Request who-has 10.0.0.3 tell 10.0.0.1, length 28
11:02:56.916991 IP 192.168.1.21.51408  192.168.1.14.4789: VXLAN, flags 
[I] (0x08), vni 10

ARP, Reply 10.0.0.3 is-at fa:16:3e:e6:e1:c8, length 28
11:02:56.917282 IP 

Re: [openstack-dev] [neutron] VXLAN with single-NIC compute nodes: Avoiding the MTU pitfalls

2015-03-11 Thread Ian Wells
On 11 March 2015 at 04:27, Fredy Neeser fredy.nee...@solnet.ch wrote:

 7: br-ex.1: BROADCAST,MULTICAST,UP,LOWER_UP mtu 1500 qdisc noqueue state
 UNKNOWN group default
 link/ether e0:3f:49:b4:7c:a7 brd ff:ff:ff:ff:ff:ff
 inet 192.168.1.14/24 brd 192.168.1.255 scope global br-ex.1
valid_lft forever preferred_lft forever

 8: br-ex.12: BROADCAST,MULTICAST,UP,LOWER_UP mtu 1554 qdisc noqueue
 state UNKNOWN group default
 link/ether e0:3f:49:b4:7c:a7 brd ff:ff:ff:ff:ff:ff
 inet 192.168.1.14/24 brd 192.168.1.255 scope global br-ex.12
valid_lft forever preferred_lft forever


I find it hard to believe that you want the same address configured on
*both* of these interfaces - which one do you think will be sending packets?

You may find that configuring a VLAN interface for eth1.12 (not in a
bridge, with a local address suitable for communication with compute nodes,
for VXLAN traffic) and eth1.1 (in br-ex, for external traffic to use) does
better for you.

I'm also not clear what your Openstack API endpoint address or MTU is -
maybe that's why the eth1.1 interface is addressed?  I can tell you that if
you want your API to be on the same address 192.168.1.14 as the VXLAN
tunnel endpoints then it has to be one address on one interface and the two
functions will share the same MTU - almost certainly not what you're
looking for.  If you source VXLAN packets from a different IP address then
you can put it on a different interface and give it a different MTU - which
appears to fit what you want much better.
-- 
Ian.
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Re: [openstack-dev] [neutron] VXLAN with single-NIC compute nodes: Avoiding the MTU pitfalls

2015-03-11 Thread Fredy Neeser

[resent with a clarification of what [6] is doing towards EoM]


OK, I looked at the devstack patch

   [6] Configure mtu for ovs with the common protocols

but no -- it doesn't do the job for the VLAN-based separation
of native and encapsulated traffic, which I'm using in [1] for
a clean (correct MTUs ...) VXLAN setup with single-NIC compute nodes.

As shown in Figure 2 of [1], I'm using VLANs 1 and 12 for native
and encapsulated traffic, respectively.  I needed to manually
create br-ex ports br-ex.1 (VLAN 1) and br-ex.12 (VLAN 12) and
configure their MTUs.  Moreover, I needed a small VLAN awareness
patch to ensure that the Neutron router gateway port qg-XXX uses VLAN 1.


Consider the example below:

Example

# ip a
...
2: eth0: BROADCAST,MULTICAST,UP,LOWER_UP mtu 1554 qdisc pfifo_fast 
master ovs-system state UP group default qlen 1000

link/ether e0:3f:49:b4:7c:a7 brd ff:ff:ff:ff:ff:ff
...
6: br-ex: BROADCAST,MULTICAST,UP,LOWER_UP mtu 1554 qdisc noqueue state 
UNKNOWN group default

link/ether e0:3f:49:b4:7c:a7 brd ff:ff:ff:ff:ff:ff

7: br-ex.1: BROADCAST,MULTICAST,UP,LOWER_UP mtu 1500 qdisc noqueue 
state UNKNOWN group default

link/ether e0:3f:49:b4:7c:a7 brd ff:ff:ff:ff:ff:ff
inet 192.168.1.14/24 brd 192.168.1.255 scope global br-ex.1
   valid_lft forever preferred_lft forever

8: br-ex.12: BROADCAST,MULTICAST,UP,LOWER_UP mtu 1554 qdisc noqueue 
state UNKNOWN group default

link/ether e0:3f:49:b4:7c:a7 brd ff:ff:ff:ff:ff:ff
inet 192.168.1.14/24 brd 192.168.1.255 scope global br-ex.12
   valid_lft forever preferred_lft forever


# ovs-vsctl show
c0618b20-1eeb-486c-88bd-fb96988dbf96
Bridge br-tun
Port patch-int
Interface patch-int
type: patch
options: {peer=patch-tun}
Port br-tun
Interface br-tun
type: internal
Port vxlan-c0a80115
Interface vxlan-c0a80115
type: vxlan
options: {df_default=true, in_key=flow, 
local_ip=192.168.1.14, out_key=flow, remote_ip=192.168.1.21}


Bridge br-ex
Port phy-br-ex
Interface phy-br-ex
type: patch
options: {peer=int-br-ex}
Port br-ex.12
tag: 12
Interface br-ex.12
type: internal
Port br-ex.1
tag: 1
Interface br-ex.1
type: internal
Port eth0
tag: 1
trunks: [1, 12]
Interface eth0
Port qg-e046ec4e-e3
tag: 1
Interface qg-e046ec4e-e3
type: internal
Port br-ex
Interface br-ex
type: internal

/Example


My home LAN (external network) is enabled for Jumbo frames, as can be
seen from eth0's MTU of 1554, so my path MTU for VXLAN is 1554 bytes.

VLAN 12 supports encapsulated traffic with an MTU of 1554 bytes.

This allows my VMs to use the standard MTU of 1500 regardless
of whether they are on different compute nodes (so they communicate
via VXLAN) or on the same compute node, i.e., the effective
L2 segment MTU is 1500 bytes.  Because this is the default,
I don't need to change guest MTUs at all.

For bridge br-ex, I configured two internal ports br-ex.{1,12}
as shown in the table below:

  br-ex VLAN MTURemarks
  Port
  --
  br-ex.1  11500
  br-ex.12121554
  br-ex Unused
  qg-e046ec4e-e3   1VLAN awareness patch (cf. [1])


All native traffic (including routed traffic to/from a Neutron router
and traffic generated by the Network Node itself) uses VLAN 1 on
my LAN, with an MTU of 1500 bytes.

For my small VXLAN test setup, I didn't need to assign different IPs to
br-ex.1 and br-ex.12, both are assigned 192.168.1.14/24.

So why doesn't [6] do the right thing? --

Well, obviously [6] does not add the VLAN awareness that I need
for the Neutron qg-XXX gateway ports.

Moreover, [6] tries to auto-configure the L2 segment MTU based on
guessing the path MTU by determining the MTU of an interface associated
with $TUNNEL_ENDPOINT_IP, which is 192.168.1.14 in my case.

It does this essentially by querying

  # ip -o address | awk /192.168.1.14/ {print \$2}

getting the MTU of that interface and then subtracting out the overhead
for VXLAN encapsulation.

However, in my case, the above lookup would return *two* interfaces:
  br-ex.1
  br-ex.12
so the patch [6] wouldn't know which interface's MTU it should take.

Also, when I'm doing VLAN-based traffic separation for an overlay
setup using single-NIC nodes, then I already know both the
L3 path MTU and the desired L2 segment MTU.


I'm currently checking if the MTU selection and advertisement patches
[3-5] are compatible with the VLAN-based traffic separation [1].


Regards

Fredy Neeser
http://blog.systeMathic.ch


On 06.03.2015 18:37, Attila Fazekas wrote:


Can 

Re: [openstack-dev] [neutron] VXLAN with single-NIC compute nodes: Avoiding the MTU pitfalls

2015-03-11 Thread Fredy Neeser

OK, I looked at the devstack patch

   [6] Configure mtu for ovs with the common protocols

but no -- it doesn't do the job for the VLAN-based separation
of native and encapsulated traffic, which I'm using in [1] for
a clean (correct MTUs ...) VXLAN setup with single-NIC compute nodes.

As shown in Figure 2 of [1], I'm using VLANs 1 and 12 for native
and encapsulated traffic, respectively.  I needed to manually
create br-ex ports br-ex.1 (VLAN 1) and br-ex.12 (VLAN 12) and
configure their MTUs.  Moreover, I needed a small VLAN awareness
patch to ensure that the Neutron router gateway port qg-XXX uses VLAN 1.


Consider the example below:

Example

# ip a
...
2: eth0: BROADCAST,MULTICAST,UP,LOWER_UP mtu 1554 qdisc pfifo_fast 
master ovs-system state UP group default qlen 1000

link/ether e0:3f:49:b4:7c:a7 brd ff:ff:ff:ff:ff:ff
...
6: br-ex: BROADCAST,MULTICAST,UP,LOWER_UP mtu 1554 qdisc noqueue state 
UNKNOWN group default

link/ether e0:3f:49:b4:7c:a7 brd ff:ff:ff:ff:ff:ff

7: br-ex.1: BROADCAST,MULTICAST,UP,LOWER_UP mtu 1500 qdisc noqueue 
state UNKNOWN group default

link/ether e0:3f:49:b4:7c:a7 brd ff:ff:ff:ff:ff:ff
inet 192.168.1.14/24 brd 192.168.1.255 scope global br-ex.1
   valid_lft forever preferred_lft forever

8: br-ex.12: BROADCAST,MULTICAST,UP,LOWER_UP mtu 1554 qdisc noqueue 
state UNKNOWN group default

link/ether e0:3f:49:b4:7c:a7 brd ff:ff:ff:ff:ff:ff
inet 192.168.1.14/24 brd 192.168.1.255 scope global br-ex.12
   valid_lft forever preferred_lft forever


# ovs-vsctl show
c0618b20-1eeb-486c-88bd-fb96988dbf96
Bridge br-tun
Port patch-int
Interface patch-int
type: patch
options: {peer=patch-tun}
Port br-tun
Interface br-tun
type: internal
Port vxlan-c0a80115
Interface vxlan-c0a80115
type: vxlan
options: {df_default=true, in_key=flow, 
local_ip=192.168.1.14, out_key=flow, remote_ip=192.168.1.21}


Bridge br-ex
Port phy-br-ex
Interface phy-br-ex
type: patch
options: {peer=int-br-ex}
Port br-ex.12
tag: 12
Interface br-ex.12
type: internal
Port br-ex.1
tag: 1
Interface br-ex.1
type: internal
Port eth0
tag: 1
trunks: [1, 12]
Interface eth0
Port qg-e046ec4e-e3
tag: 1
Interface qg-e046ec4e-e3
type: internal
Port br-ex
Interface br-ex
type: internal

/Example


My home LAN (external network) is enabled for Jumbo frames, as can be
seen from eth0's MTU of 1554, so my path MTU for VXLAN is 1554 bytes.

VLAN 12 supports encapsulated traffic with an MTU of 1554 bytes.

This allows my VMs to use the standard MTU of 1500 regardless
of whether they are on different compute nodes (so they communicate
via VXLAN) or on the same compute node, i.e., the effective
L2 segment MTU is 1500 bytes.  Because this is the default,
I don't need to change guest MTUs at all.

For bridge br-ex, I configured two internal ports br-ex.{1,12}
as shown in the table below:

  br-ex VLAN MTURemarks
  Port
  --
  br-ex.1  11500
  br-ex.12121554
  br-ex Unused
  qg-e046ec4e-e3   1VLAN awareness patch (cf. [1])


All native traffic (including routed traffic to/from a Neutron router
and traffic generated by the Network Node itself) uses VLAN 1 on
my LAN, with an MTU of 1500 bytes.

For my small VXLAN test setup, I didn't need to assign different IPs to
br-ex.1 and br-ex.12, both are assigned 192.168.1.14/24.

So why doesn't [6] do the right thing? --

Well, obviously [6] does not add the VLAN awareness that I need
for the Neutron qg-XXX gateway ports.
Moreover, [6] tries to auto-configure the L2 segment MTU based on
determining the MTU of an interface associated with
$TUNNEL_ENDPOINT_IP, which is 192.168.1.14 in my case.

It does this essentially by querying

  # ip -o address | awk /192.168.1.14/ {print \$2}

However, in my case, this would return *two* interfaces:
  br-ex.1
  br-ex.12
so the patch [6] wouldn't know which interface's MTU it should take.


I'm currently checking if the MTU selection and advertisement patches
[3-5] are compatible with the VLAN-based traffic separation [1].


Regards

Fredy Neeser
http://blog.systeMathic.ch


On 06.03.2015 18:37, Attila Fazekas wrote:


Can you check is this patch does the right thing [6]:

[6] https://review.openstack.org/#/c/112523/6

- Original Message -

From: Fredy Neeser fredy.nee...@solnet.ch
To: openstack-dev@lists.openstack.org
Sent: Friday, March 6, 2015 6:01:08 PM
Subject: [openstack-dev] [neutron] VXLAN with single-NIC compute nodes:  
Avoiding the MTU pitfalls

Hello world

I recently 

Re: [openstack-dev] [neutron] VXLAN with single-NIC compute nodes: Avoiding the MTU pitfalls

2015-03-06 Thread Attila Fazekas
Can you check is this patch does the right thing[1]:

[1] https://review.openstack.org/#/c/112523/6

- Original Message -
 From: Fredy Neeser fredy.nee...@solnet.ch
 To: openstack-dev@lists.openstack.org
 Sent: Friday, March 6, 2015 6:01:08 PM
 Subject: [openstack-dev] [neutron] VXLAN with single-NIC compute nodes:   
 Avoiding the MTU pitfalls
 
 Hello world
 
 I recently created a VXLAN test setup with single-NIC compute nodes
 (using OpenStack Juno on Fedora 20), conciously ignoring the OpenStack
 advice of using nodes with at least 2 NICs ;-) .
 
 The fact that both native and encapsulated traffic needs to pass through
 the same NIC does create some interesting challenges, but finally I got
 it working cleanly, staying clear of MTU pitfalls ...
 
 I documented my findings here:
 
[1]
 http://blog.systemathic.ch/2015/03/06/openstack-vxlan-with-single-nic-compute-nodes/
[2]
 http://blog.systemathic.ch/2015/03/05/openstack-mtu-pitfalls-with-tunnels/
 
 For those interested in single-NIC setups, I'm curious what you think
 about [1]  (a small patch is needed to add VLAN awareness to the
 qg-XXX Neutron gateway ports).
 
 
 While catching up with Neutron changes for OpenStack Kilo, I came across
 the in-progress work on MTU selection and advertisement:
 
[3]  Spec:
 https://github.com/openstack/neutron-specs/blob/master/specs/kilo/mtu-selection-and-advertisement.rst
[4]  Patch review:  https://review.openstack.org/#/c/153733/
[5]  Spec update:  https://review.openstack.org/#/c/159146/
 
 Seems like [1] eliminates some additional MTU pitfalls that are not
 addressed by [3-5].
 
 But I think it would be nice if we could achieve [1] while coordinating
 with the MTU selection and advertisement work [3-5].
 
 Thoughts?
 
 Cheers,
 - Fredy
 
 Fredy (Freddie) Neeser
 http://blog.systeMathic.ch
 
 
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