Catalyst 9500 DHCP infinite leasing even for future leaseouts

[Aaron_un]

I configured a 9500 as a DHCP server to give out unlimited leases

ip dhcp pool Vlan100

 network 10.1.0.0 255.255.254.0

 dns-server x.y.z

 default-router x.y.z

 lease infinite

as you can see I have 510 ips for this network, now let's say max number of ppl who are connecting to this network at a time won't surpass 200(but number of unique people/macs are below 490), so old IPs won't be needed to be retaken.

does the DHCP server will still keep the old MACs in the memory so if the same host connects to the network, can be handed the same IP that has been handed out last time? if not how can we achieve that?

now please remember this is a dynamic question I don't have the ability to make all of them binded one by one by mac.

thanks

[balaji.bandi]

what is the version of code running ?

can you post show mac address table ?

[Aaron_un]

hello balaji, idk why you need to see the output of show mac add table, I think what you're lookin for is sh ip dhcp binding

I have both of those outputs, I have access to the leased macs, but I don't have access to the macs that are not currently under lease and can't be predicted before they are connected...

again this is a dynamic question, how can we keep the bindings dynamically in the memory, I don't even know if it does that automatically...

if I am not wrong it doesn't automatically assign the ips that way, once the ip gets free(disconnected) and it's available it will be handed to another device, even that we have IPs that never been used...

[balaji.bandi · Accepted solution]

what is the version of code running on the kit ---asked before also.

Why i have asked the MAC address table to look at how long it resides in the cache? some time due to bug they may stuck not cleared or uses some time default time value.

if I am not wrong it doesn't automatically assign the ips that way, once the ip gets free(disconnected) and it's available it will be handed to another device, even that we have IPs that never been used...

This needs to understand how the setup at your side, Technically that way it works as long as it free, it should be removed depends on lease time.

what DHCP Server is this ? what you see on DHCP ? is the IP and MAC address still there, which switch don't have the same MAC Address? 

[Aaron_un · Accepted solution]

sry I forgot that

Cisco IOS Software [Gibraltar], Catalyst L3 Switch Software (CAT9K_IOSXE), Version 16.12.4, RELEASE SOFTWARE (fc5)



SW1#show mac address-table aging-time
Global Aging Time: 300
Vlan Aging Time
---- ----------
SW1#

This 9500 is only acting as the DHCP server, requests are being relayed to her, so she doesn't have the mac to those devices on his mac address table since they are not directly connected.

again my pool has infinite lease period

ip dhcp pool Vlan100
 network 10.1.0.0 255.255.254.0
 lease infinite

oh btw I still see that specific device mac in the table, from 2 days ago that I connected and I brought it back home, so I guess it's working so far, I mistakenly thought at the first place because it's in the table then it has to be connected to the network as well and didn't verify the mac address lol (0134.4 this is actually the mac-id of my computer) but that's what suppose to happen when you make it infinite and that's what I was looking for too at the first place, again crazy!(sometimes we people just don't wanna believe something is working)

SW1#show ip dhcp binding | inc 10.1.
10.1.0.1 0134.4xxx.xxxx.xx Infinite Automatic Active TwentyFiveGigE2/0/1
10.1.0.2 xxxx.xxxx.xxxx Infinite Automatic Active TwentyFiveGigE2/0/1
10.1.0.3
10.1.0.4
10.1.0.5

.

.

.

so in conclusion, I think that mac binding will remain there until the whole pool of 510 being depleted and 511th device being connected, or the switch power cycles

[balaji.bandi]

I can understand, Glad all good and you could able to understand the system correctly - the Cisco community always helps each other with knowledge and experience, Learning never ends in technology.