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Some clients can not get IP from DHCP Server in USG6300

Publication Date:  2015-10-29 Views:  69 Downloads:  0
Issue Description

There are two DHCP Pools(pool10 and pool20) in USG6300, and the customer said that Pool20 was working normal, but clients behind  pool10 got no IP address, and only a few clients who already had a lease were able to renew their lease, and had normal access to the internet.

The IP pool information is as below:

Pool name pool20

gateway-list 10.20.0.1

dns-list 8.8.8.8

expired day 1 hour 0 minute 0

ip-range 10.20.0.10  10.20.249.254

mask 255.255.0.0

 

Pool name pool10

gateway-list 10.10.0.1

dns-list 8.8.8.8

expired day 1 hour 0 minute 0

ip-range 10.10.0.10  10.10.254.254

mask 255.255.0.0

This is the topology:

Alarm Information
None
Handling Process

(1)    Asked the customer to capture data packets from client which can’t get IP from USG6300. It turned out no reply from USG6300.

(2)    Get the debug message

<USG6300>debugging dhcp server all 

<USG6300>terminal debugging

Info: Current terminal debugging is on.

<USG6300>terminal monitor

Info: Current terminal monitor is on.

     <USG6300>

And we found there were many logs in below:

DhcpServer: receive DHCPDISCOVER from 8CFA-xxxx-9FCB

*1.267645384 Guest-FW DHCPS/7/DHCPS_DEBUG_COMMON:

DhcpServer:Too many DHCP Leases

*1.267645384 Guest-FW DHCPS/7/DHCPS_DEBUG_COMMON:

DhcpServer: Register Lease Failed

The message “Too many DHCP Leases” indicated the current assigned IP reached the specification list of USG6300, so USG6300 can’t assign new IP anymore.

(3)    Check the specification list of USG6300, and found that USG6300 can support 8192 client in total. But the customer told us that there were only more than clients online.

We found there are still free IP in both IP Pool Pool10 and Pool20.

<USG6300>display dhcp server free-ip

14:51:02  2015/09/16

Global pool:

Interface pool:

Pool name: Pool20

IP Range from 10.20.32.85          to  10.20.249.254      

Pool name: Pool10

IP Range from 10.10.0.18           to  10.10.0.125

IP Range from 10.10.0.127          to  10.10.254.0        

IP Range from 10.10.254.7          to  10.10.254.254  

 

Check the output of the following commands:

<Guest-FW>display dhcp server ip-in-use all

We found from the output that there were only 5030 client(5020 client for IP Pool20, and 10 client for IP Pool10) . From here, we can see the number of client is less that the specification list (8192 clients)

(4)    Check the output of the following command:

<USG6300>display dhcp server conflict all

And found that for IP Pool20, there were 82 IPs, which can used for new clients from the same network 10.20.0.0/16. For IP Pool10, there were only 2 IPs.

Check the output of the following command:

<USG6300>display dhcp server expired all

And found that there were 3080 IPs, and all of them are for IP Pool20, but those IP can only be used for IP Pool20.

The root cause was clear. Even the number of client(5030) didn’t reach the specification list(8192), but some IPs in conflict list and expired list would consume the number of specification list, and they can’t be used by other IP Pools. That is why for IP pool20, clients can get IP, but for IP Pool10, client can’t get IP.

Root Cause

Even the number of clients(5030) didn’t reach the specification list(8192), but some IPs in conflict list and expired list would consume the number of specification list, and they can’t be used by other IP Pools. That is why for IP pool20, clients can get IP, but for IP Pool10, client can’t get IP.

Solution

1.     Reboot the USG6300, the conflict list and expired list will be reset, then client from IP Pool10 can get IP.

2.     Redesign the IP Pool. It’s not a good idea to set a IP Pool have 65535 IP. The customer set IP Pool20 only 5000 ip, and the rest 3192 is for IP Pool10.

Suggestions

When you configure IP Pool in USG6300, you should design the IP segment according to real need.

END