Vlan translation on Arista EOS

Simple topology:

[vlan 509]==> e17/1:: DCS-7170-32C-F :: po5 [vlan 309]

Requirement:

* ingress traffic with vlan tag 509 at et17/1

* like to translate it to vlan tag 309 on egress intf - po5

Configuration:

interface Port-Channel5

   description egress::po5

   switchport trunk native vlan 399

   switchport trunk allowed vlan 300-321,330,399,503,509

   switchport mode trunk

   switchport vlan translation 309 509

Syntax:

  switchport vlan translation <vlan_map_from> <vlan_map_to>

Please note: the vlan # from and to in above syntax is from the incoming point of view

"no-internal-vlan" error for routed interfaces

Creating several L3 routed port-channels and sub-interfaces, but they failed to come up with errdisabled status. The output "show interface status err" displays the following reasons:

yo411.16:22:08(config-if-Po1201)#show int status errdisabled
   Port           Name             Status         Reason
-------------- ---------------- ----------------- ---------------------
   Et3/12/1                        errdisabled    port-channel-shutdown
   Et4/12/1                        errdisabled    port-channel-shutdown
   Po1201.3                        errdisabled    no-internal-vlan
   Po1201.2                        errdisabled    no-internal-vlan
   Po1201                          errdisabled    no-internal-vlan

Basically, the "port-ch-shutdown" error was caused by the Po1201 being down. Checked the EOS document, the system will reserve an internal VLAN for any "no switchport" interfaces. And the internal VLAN ranges start from 1006 to 4094 (ref: EOS Manual section 19.4.3)

yo411.16:22:59(config-if-Po1201)#show vlan internal usage
1006  Port-Channel1900.4002
1007  Ethernet3/36/3
1008  Port-Channel1900
1009  Ethernet3/36/1
1010  Port-Channel1900.4003
1011  Ethernet3/36/4
1012  Ethernet3/36/2
1013  Ethernet3/36/4.2
1014  Ethernet3/36/4.3

And internal VLAN assignment stops at 1015. 

yo411.16:23:23(config-if-Po1201)#sh vlan 1015
VLAN  Name                             Status    Ports
----- -------------------------------- --------- -------------------------------
1015  VLAN1015                         suspended

So the root cause is that there is an accidental configuration of vlan 1015 with a suspended state, and this blocks the internal VLAN assignment. 

yo411.16:24:19(config)#no vlan 1006 - 1099
yo411.16:24:36(config)#sh int status errdisabled

After removing the VLAN configuration, there is no internal-VLAN error anymore. 

yo411.16:24:47(config)#show vlan internal usage
...
1015  Port-Channel1201.2
1016  Port-Channel1201.3
1017  Port-Channel1201

Another way is to specify the internal VLAN range to an unused space (ref: EOS manual section 21.3) 

yo411(config)# vlan internal order descending range 4000 4094

Arista EOS: trunk group

From the below link of "MLAG - basic configuration", there have the following configuration of MLAG peer link VLAN:

vlan 4094
  trunk group peerLink
interface port-ch 2000 
  switch trunk group peerLink

Why do we need to assign vlan 4094 to trunk group? Quota from the reference of EOS configuration - VLAN,  

"VLANs configured in a trunk group are 'pruned' off all ports that are not associated with the trunk group". 

• So if you have other ethernet or port-channels are configured as trunk, by default ALL VLANs are enabled if you don't specify the VLAN range. In this case, peerLink VLAN is also included. This is not an expected behavior or good practice, since the peerLink carries the critical control plane information. 
• But if you configure VLAN in trunk group, you have to specify the physical interfaces are associated with this trunk group. This is to provide a casual configuration causing the disruption of peerLink Vlan