02-18-2015 02:35 AM - edited 03-07-2019 10:43 PM
I am encountering a weird anomaly while trying to reserve DHCP address in a CISCO 3750.
Basically, for MAC address AAAA.BBBB.CCCC I want to reserve IP 1.1.1.7, which is in the DHCP pool range.
In the DHCP config I have added the reservation:
address 1.1.1.7 hardware-address AAAA.BBBB.CCCC
However, instead of the 1.1.1.7 IP address, I get assigned another one 1.1.1.4 which in the show binding config shows as
1.1.1.4 hardware-address 01AA.AABB.BBCC.CC Feb Auto
1.1.1.7 hardware-address AAAA.BBBB.CCCC Inf Manual
As it can be seen, the MAC address is shifted and a '01' is added at its start.
In the DHCP pool it displays correctly as:
address 1.1.1.7 hardware-address AAAA.BBBB.CCCC
So what went wrong and how can I fix this ?
Solved! Go to Solution.
02-18-2015 03:01 AM
Hi,
In DHCP messages, clients usually identify themselves using the DHCP Option 61, also called the Client ID option. If this option is present in a DHCP client message, IOS will use the Client ID and not the MAC address of the client to look up the static binding.
The "01" at the beginning of the Client ID means that this is an Ethernet MAC address (basically, it is a type identifier). So in order to make your assignments work, replace the hardware-address AAAA.BBBB.CCCC with client-identifier 01AA.AABB.BBCC.CC and it should work.
You may also be interested in checking out these two threads that discuss the same issue:
https://supportforums.cisco.com/discussion/12261746/dhcp-static-lease-cisco-2811
Best regards,
Peter
02-18-2015 03:01 AM
Hi,
In DHCP messages, clients usually identify themselves using the DHCP Option 61, also called the Client ID option. If this option is present in a DHCP client message, IOS will use the Client ID and not the MAC address of the client to look up the static binding.
The "01" at the beginning of the Client ID means that this is an Ethernet MAC address (basically, it is a type identifier). So in order to make your assignments work, replace the hardware-address AAAA.BBBB.CCCC with client-identifier 01AA.AABB.BBCC.CC and it should work.
You may also be interested in checking out these two threads that discuss the same issue:
https://supportforums.cisco.com/discussion/12261746/dhcp-static-lease-cisco-2811
Best regards,
Peter
02-18-2015 03:52 AM
I have removed the hardware-address-based binding.
I then cleared the binding for the .4 IP.
Then I re-added the binding with client-id instead of hardware-address.
Now binding shows:
1.1.1.7 hardware-address 01AA.AABB.BBCC.CC Inf Manual
which is correct.
From my initial tests it appears to be working correctly. The new IP address was assigned to the client.
02-18-2015 03:04 AM
Have you configured client-identifier:
Router(config)# ip dhcp pool Test
Router(dhcp-config)# host 10.10.10.10 255.255.255.0
Router(dhcp-config)# client-identifier unique-identifier << 01 followed by Mac address
Refer here and compare your config: http://www.cisco.com/c/en/us/td/docs/ios/12_2/ip/configuration/guide/fipr_c/1cfdhcp.html#wp1001108
If you still have issues post your complete DHCP config and sh ip dhcp bin
-Terry
02-18-2015 03:54 AM
host cannot be configured under ip dhcp pool --> This command may not be used with network, origin, vrf or relay pools.
Probably that would be fine on static a pool.
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