# Help with incomplete arp entry, possible vlan issue



## giannidoe (Feb 18, 2011)

I've just transferred an 8.1 server to a new data centre and it is unable to communicate with the default gateway, whilst a linux box transferred at the same time works fine.
The entry in the ARP table for the gateway is incomplete even though I can see ARP requests and responses.


```
# arp -an
? (xx.xx.113.1) at (incomplete) on rl0 [ethernet]
```


```
00:00:00.000079 00:1d:0f:c3:35:5e > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has xx.xx.113.1 tell xx.xx.113.66, length 46
00:00:00.000180 00:1e:14:27:34:1a > 00:1d:0f:c3:35:5e, ethertype 802.1Q (0x8100), length 64: vlan 401, p 0, ethertype ARP, Reply xx.xx.113.1 is-at 00:1e:14:27:34:1a, length 46
00:00:00.000069 00:1d:0f:c3:35:5e > ff:ff:ff:ff:ff:ff, ethertype ARP (0x0806), length 60: Request who-has xx.xx.113.1 tell xx.xx.113.66, length 46
00:00:00.000210 00:1e:14:27:34:1a > 00:1d:0f:c3:35:5e, ethertype 802.1Q (0x8100), length 64: vlan 401, p 0, ethertype ARP, Reply xx.xx.113.1 is-at 00:1e:14:27:34:1a, length 46
```

Any ideas why the ARP table is not getting populated correctly?


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## Alt (Feb 18, 2011)

In your tcpdump its saying your GW in vlan 401, but on arp -an output it excepting this arp on rl0.
Show ifconfig, possibly its wrong vlan config


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## giannidoe (Feb 18, 2011)

I've not configured any vlans, do I need to? linux and windows boxes on the same network just set the default gw and it works without any specific vlan config.


```
# ifconfig rl0
rl0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
	options=8<VLAN_MTU>
	ether 00:1d:0f:c3:35:5e
	inet xx.xx.113.66 netmask 0xffffff00 broadcast xx.xx.113.255
	media: Ethernet autoselect (100baseTX <full-duplex>)
	status: active
```


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## giannidoe (Feb 18, 2011)

PS. if I add the arp entry manually I can communicate with the gw, but I'd obviously prefer not to do this.

```
arp -s xx.xx.113.1 00:1e:14:27:34:1a
```


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## SirDice (Feb 18, 2011)

giannidoe said:
			
		

> I've not configured any vlans, do I need to?


Currently, yes.



> linux and windows boxes on the same network just set the default gw and it works without any specific vlan config.


Ask the people at the datacenter to correctly configure the switchport the machine is connect to. It's currently trunked.


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## giannidoe (Feb 18, 2011)

I'll ask them to reconfigure the switch port.

I've not any experience with VLANs; if I were to configure a vlan to access the gw on xx.xx.113.1 how would I go about doing this, would I need to assign a different address to rl0 and then define a vlan (401) for xx.xx.113.0/24 or can I somehow also keep the same xx.xx.113.66 IP address on rl0?


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## Alt (Feb 18, 2011)

You have 2 ways:
1. Something like this (i dont remebmer literally)

```
#remove ip from rl0
ifconfig vlan401 create vlandev rl0 vlan 401
#set ip to vlan401
```
2. Or, you can just ask these guys to make your port access-mode

Dunno which way is better=)


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## giannidoe (Feb 18, 2011)

I got the port configured properly and all working 
Good to know about the vlan stuff for future reference.


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## atarge (Sep 10, 2018)

giannidoe said:


> I got the port configured properly and all working
> Good to know about the vlan stuff for future reference.


can you please let me know ...how did you configured the Port Properly; i mean the configuration??


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## phoenix (Sep 11, 2018)

The switch port was configured to allow tagged vlan 401 only. Any packets that didn't have a vlan header with 401 in it would be dropped by the switch.

They reconfigured the switch to allow untagged packets (aka "normal" packets) and everything started working.


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