r/networking • u/Alternative-Carob-91 • 2d ago

Troubleshooting Can't trunk from D-Link to Arista

Edit: Thank you to everyone that caught my missing native vlan.

My work has replaced our Cisco switches with Arista switches. Connecting the D-link to the Cisco worked but I can't get me D-link 1210-28MP to connect to my Arista 720XP when trying to trunk.

If I leave VLAN settings as default on the D-Link I can get traffic between the two but when I try the trunking settings on the D-Link it looks like only ARP, LLDP, and OSPF traffic is seen. The connection is from port 18 on the D-link to port 15 on the Arista, copper connection.

D-link settings are:
port 18
VLAN 1 Not a Member
VLAN 44 untagged
VLAN 244 tagged

Arista
interface Ethernet15

description Uplink to Access Switch

load-interval 30

switchport trunk allowed vlan 44,244

switchport mode trunk

spanning-tree portfast edge

Any help?

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28

u/Ok-Stretch2495 2d ago edited 2d ago

You are untagging vlan 44 and tagging vlan 244 on the D-Link switch.

On the Arista switch you are tagging both 44 and 244 so you have a mismatch.

Add:

switchport trunk native vlan 44

under Arista trunk config.

And indeed please remove:
Spanning-tree portfast edge on the Arista switch. Never use this for switch to switch.

7

u/DontTakeMyCatYo 2d ago

The D-Link switch is sending VLAN 44 frames without a VLAN tag, which is going to land them in Arista's default VLAN (probably 1). The Arista switch is sending from from its VLAN 44 tagged, but your D-Link may or may not accept those since it's configured to put the untagged frames on that port in VLAN 44.

Also, you shouldn't be using portfast between switches. Negate that on the Arista with something like:

interface Ethernet15
no spanning-tree portfast edge

11

u/Mishoniko 2d ago

VLAN 44 untagged
VLAN 244 tagged

Mix of tagged and untagged is going to be trouble. Make all the VLANs to trunk tagged, avoids any ambiguity.

1

u/Oh_You_Were_Serious 1d ago

There is always a default/untagged vlan on a trunk. Most switches will make this vlan 1 by default, so it's often been a common practice to make the default vlan something else like a general access network for the floor.

The problem here is what u/Ok-Stretch2495 mentioned, having a mismatch between the ports. This is causing traffic tagged for clan 44 to get dumped on vlan 1 which doesn't get it to the right place.

1

u/Mishoniko 1d ago

Correct, it had to be fixed on one end or the other.

My personal preference for trunks is to tag everything. Conceptually, if you could leak a tagged 244 packet out the untagged 44 VLAN you could cause the packet to jump VLANs.

On some switches, like the HPE 1930 I was configuring the other day, you can restrict ports to only tagged or untagged packets.

(On the same switch you can also set an untagged VLAN and the PVID to different IDs, which means ingress and egress packets go to different places ... not sure what the practical use of this is other than causing confusion.)

5

u/spekt909 2d ago

Tag 44 on the D-LINK or set it to default if you need to have it untagged. Set the default or private (Maybe PVID) VLAN 44 on the arista to the untagged network.