how to release expired IP's for a particular VLAN in summit x460-24t switch

  • 5 July 2017
  • 8 replies
  • 684 views

hi
We have above extreme networks switch .
We have created avlan 1967 with ip 172.16.92.1/24
It gives IP via DHCP in range 172.16.92.2-172.16.92.250
When we connect a device with new MAC ID , an IP gets reserved for it which expires after 2 hours.
We are connecting (and removing) a lot of devices with unique MAC ID on this vlan , as a result pool is getting exhausted.

#Show vlan1967 dhcp-address-allocation
shows a lot of entries for different mac addresses with state as expired and assigned .
How can I get expired IP released automatically ?

Thanks.

8 replies

Userlevel 3
clear vlan vlan_name dhcp-address-allocation [[all {offered | assigned | declined
| expired}] | ipaddress]

Should do the job.
"clear vlan vlan1967 dhcp-address-allocation all expired " works.

thanks Hagemann, Olaf, Employee .

Any way that switch automatically releases expired IP's ?
Userlevel 4
"clear vlan vlan1967 dhcp-address-allocation all expired " works.

thanks Hagemann, Olaf, Employee .

Any way that switch automatically releases expired IP's ?
Try to decrease a lease time
Userlevel 5
Hi

configure vlan vlan_name dhcp-lease-timer
http://documentation.extremenetworks.com/exos_commands_22.2/exos_21_1/exos_commands_all/r_configure-...

Best regards
My current lease timer is default i.e 7200 seconds.
Say , a device is connected it gets IP then the device is removed .
I guess , the IP will become expired after 7200 seconds of assignment OR is it half the interval ?
WIll the system clear the expired IP by itself if DHCP pool is exhausted (I mean , lot of expired IP's though devices connected are few) and a new device (unique MAC) is requesting IP ?
Userlevel 4
Hi Sumeet,

Yes, the IP address will become expired after 7200 second (default) or configured lease-timer if the device is removed (It looks like DHCP client sends DHCP lease renewal every half of lease period by sending DHCP request message for the IP address).

When I did simple test in local lab, it looks like the output of "dhcp-address-allocation" just shows expired hosts without erasing them (I can see this output until now even though they were expired at 4 hours ago).

* HOON-SW2.12 # sh vlan "DHCPVLAN" dhcp-address-allocation
===============================================================================
IP MAC State Lease Time Left
===============================================================================
77.1.1.10 50:7b:9d:d5:8e:ce Expired 0000:00:00
77.1.1.11 28:d2:44:8a:8d:fa Expired 0000:00:00

Even though the IP addresses are shown as expired with previously assigned MAC address, when I connect new device, the IP address is assigned to the new device normally and immediately as below (Tested with just one DHCP address pool, 77.1.1.10) :

* HOON-SW2.4 # sh vlan "DHCPVLAN" dhcp-address-allocation
===============================================================================
IP MAC State Lease Time Left
===============================================================================
77.1.1.10 28:d2:44:8a:8d:fa Assigned 0000:00:07
* HOON-SW2.4 # sh vlan "DHCPVLAN" dhcp-address-allocation
===============================================================================
IP MAC State Lease Time Left
===============================================================================
77.1.1.10 28:d2:44:8a:8d:fa Assigned 0000:00:03
* HOON-SW2.4 # sh vlan "DHCPVLAN" dhcp-address-allocation
===============================================================================
IP MAC State Lease Time Left
===============================================================================
77.1.1.10 28:d2:44:8a:8d:fa Expired 0000:00:00

* HOON-SW2.6 # sh dhcp-server "DHCPVLAN"
VLAN "DHCPVLAN":
DHCP Address Range : 77.1.1.10->77.1.1.10
Netlogin Lease Timer : Not configured (Default = 10 seconds)
DHCP Lease Timer : 30 seconds
Default Gateway : 77.1.1.1
Primary DNS Server : 168.126.63.1
Ports DHCP Enabled : 7-8

===========================================================================
IP MAC State Lease Time Left
===========================================================================
77.1.1.10 50:7b:9d:d5:8e:ce Assigned 0000:00:29

So it looks like the EXOS just shows expired host list for the IP address and it does not mean the IP address is still assigned to the device.
Maybe this is to give same IP address to same device when it requests (renew or reconnect) dynamic IP address, before the cache is cleared.
to David Choi
Pretty nice verification.
To verify that expired IP is used when a new MAC device is connected .
I will use a vlan with small dhcp pool and exhaust it , then confirm.
Thanks.
Userlevel 4
to David Choi
Pretty nice verification.
To verify that expired IP is used when a new MAC device is connected .
I will use a vlan with small dhcp pool and exhaust it , then confirm.
Thanks.
Yes, Sumeet.
It would be the best to check it by yourself.

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