VLAN trunk over GRETAP tunnel: VLAN numbering makes a difference?

Installing and Using OpenWrt
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I'm currently setting up 2 AP's running the latest version of OpenWRT.

On the one AP, I have the following:

  • eth0.10, eth0.20, eth0.220: vlan's defined
  • bridge10 contains eth0.10, bridge20 contains eth0.20, bridge220 contains eth0.220
  • next I have multiple interfaces: one linked to each of those bridges
  • next multiple wireless networks, each linked to one of those interfaces.

I have a similar setup on AP2.

Next I defined a separate SSID to connect both AP's and carry my GRETAP tunnel.
I don't use WDS or mesh, it's basically a simple AP-client configuration between AP1 and AP2 linked to a separate bridge with an IP-address on both sides.
On both sides this interface is called bridge_trunk, has a local IP defined and no other interface linked to it. Only the GRETAP tunnel gets associated with this interface.

Next I defined a GRETAP tunnel, same setup on both sides, linked to the interface carrying the AP-client wireless network.
The tunnel is just called "tunnel".

Up to here, all good.
On AP1 then, I have the following config:

  • br10, contains now 2 ports: eth0.10 and I add "@tunnel.4".

On AP2, I have a similar setup:

  • br10, contains 2 ports: eth0.10 and I add "@tunnel.4".

This seems to work, I get traffic across, all good.
Now as soon as I want to use other VLAN's over the gretap tunnel, it stops working.

E.g.

  • br10 with ports eth0.10 and @tunnel.4 on both sides: works.
  • br10 with ports eth0.10 and @tunnel.9 on both sides: works.
  • br10 with ports eth0.10 and @tunnel.10 on both sides: doesn't work anymore.
  • br10 with ports eth0.10 and @tunnel.11 on both sides: doesn't work anymore.

It seems as if every VLAN number defined over the GRETAP tunnel of 10 or higher makes the tunnel stop working, but everything below 10 works?
@tunnel4-9 works, @tunnel10-up_to_whatever doesn't work anymore.

I haven't got the faintest idea what could be causing this behaviour, could anybody point me in the right direction here?

Side-note: everything else stays the same, I don't change any MTU or any other setting, just using a VLAN number over the GRETAP tunnel smaller than or greater than 10.

Thanks!

2

fwiw I used a vxlan tunnel with a similar vlans 10, 20, 30, 40 and it's working fine.
https://forum.openwrt.org/t/wds-vs-gre-vs-vxlan-for-multipoint-trunk-over-wifi-links/106607
Maybe test over a wired trunk to see if you get a similar result.

1 Like
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@greybeard Did you configure the MTU additionally?
I see in that linked thread that you don't define the MTU on the VXLAN tunnel.
I see other examples sometimes where they put the MTU at 1500, I believe it's somewhere in the 1200's by default?

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I set the MTU to 1550 on the underlying link. The vxlan tunnel then defaults to an MTU of 1500.

5

Thanks for the advice, switched over my setup today from GRETAP to VXLAN, just worked out of the box without any issues.

1 Like
6

Glad you solved your issue but I'm still curious about the misbehaving you have found...
But IMHO vxlan scales "better" (and sometimes it's easier) but in case you use local multicast or routed multicast you may have to ensure if actually works... And thanks for the follow up.

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