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Unknown Router Interface in DVR Mode

asked 2018-08-07 15:00:24 -0500

codylab gravatar image

updated 2018-08-07 15:02:40 -0500

Hi everyone,

After I enabled the DVR, my tenant router gets an extra interface in addition to the tenant network gateway. That extra interface only shows up in the Horizon dashboard, not in the command line output. Does anyone know what that interface is for?

Here are some details to help explain what I encountered:

On the compute node:

[root@compute ~]# ip netns 
fip-eadd51b1-1b0a-4504-b694-4f54b7b60d3d (id: 1) 
qrouter-b7570af0-42f6-499d-bbf0-2139a98bc0a3 (id: 0)

[root@compute ~]# ip netns exec qrouter-b7570af0-42f6-499d-bbf0-2139a98bc0a3 ip addr show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet scope host lo         
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: rfp-b7570af0-4: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
    link/ether ca:08:94:69:b9:6c brd ff:ff:ff:ff:ff:ff link-netnsid 0
    inet scope global rfp-b7570af0-4
       valid_lft forever preferred_lft forever
    inet6 fe80::c808:94ff:fe69:b96c/64 scope link
       valid_lft forever preferred_lft forever
13: qr-bd3e180e-2d: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc noqueue state UNKNOWN group default qlen 1000
    link/ether fa:16:3e:c4:a8:3c brd ff:ff:ff:ff:ff:ff
    inet brd scope global qr-bd3e180e-2d
       valid_lft forever preferred_lft forever
    inet6 fe80::f816:3eff:fec4:a83c/64 scope link
       valid_lft forever preferred_lft forever

In above, the router has only one qr interface (qr-bd3e180e-2d) at IP which is the tenant network gateway, as expected.

From the Horizon dashboard:

Name                          Fixed IPs

Notice there is an extra, unknown interface (da7884d9-2ff1) at Could someone explain to me what that interface is for?

Thank you very much!

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answered 2018-08-08 07:31:03 -0500


the extra interface is the FIP (floating IP namespace), this interface makes snat/dnat in the router namespace north-south in compute hosts, the allow the floating IP traffic goes outside directly from compute nodes and not need to flow through neutron nodes.

The interface in qrouter (rfp-*) is the patch link to the FIP namespace (patch fpr).

This is the reason of needing a external bridge in compute hosts, and the usage of a free floating IP per router/node.

Check this link for more information about how DVR works.


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Thank you, Eduardo. What I don't know is the da7884d9-2ff1 interface. It only appears in the Horizon dashboard, not in the CLI output, as you can see from the attached result.

codylab gravatar imagecodylab ( 2018-08-08 12:55:47 -0500 )edit

As per the dashboard, there are 3 ports: rfp-b7570af0-4 (patched to the FIP namespace), qr-bd3e180e-2d (tenant subnet gateway), and the unknown da77884d9-2ff1, which cannot be found from the CLI result. Should there be only 2 interfaces on the router?

codylab gravatar imagecodylab ( 2018-08-08 12:57:06 -0500 )edit

whats the result of openstack port list --router ROUTER_ID and openstack port show PORT_ID

Eduardo Gonzalez gravatar imageEduardo Gonzalez ( 2018-08-09 01:34:07 -0500 )edit

I can't paste the result here due to length limit. Please check this link:

codylab gravatar imagecodylab ( 2018-08-09 10:17:30 -0500 )edit

In this case, which port does the qrouter namespace use to forward the snat traffic from the VM back to the br-int? Should it be via the same subnet gateway port (i.e. qr-bd3e180e-2d)?

codylab gravatar imagecodylab ( 2018-08-09 10:39:39 -0500 )edit

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Asked: 2018-08-07 15:00:24 -0500

Seen: 140 times

Last updated: Aug 08 '18