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DHCPDISCOVER messages - Delay in getting IP

RPedada
Techie
Posts: 6
3088     0

some clients in our environment complain about slowness in getting IP's from DHCP on wireless. We are on 7.3.11.

 

When I looked at the logs, I see several DHCPDISOVER messages but no OFFER messages. After a wait of 4-5 minutes, I see DHCPOFFER messages from IB DHCP. Did anyone see this before.

And I have looked at the client logs on a microsoft machine and it says "

Offer Receive Timeout has happened on the interface 3" for every DHCPDISOVER message that appear in the IB syslog.

 

Thanks

 

Re: DHCPDISCOVER messages - Delay in getting IP

RPedada
Techie
Posts: 6
3089     0

I think I found the problem. But I am not very sure.

 

 

We run DHCP failover. Both peers will receive DHCP broadcast traffic from clients, but only one peer will respond (based on a hash algorithm of the clients MAC address).

The failover peers are supposed to “re-balance” their lease pools so that they each have approximately 50% of the free leases available.

 

There are instances when re-balancing doesn’t work (usually on very busy networks), so one peer will run out leases and the other peer will not answer because it expects it’s partner to respond to the lease request. Normally the client would just retransmit it’s DHCPOFFER request and increase the “elapsed time” field in the DHCP packet so that the DHCP servers would see it as a retransmit (the other peer would then respond). 

Re: DHCPDISCOVER messages - Delay in getting IP

CWM0rris25
Techie
Posts: 1
3089     0

We are having the same issue. We also run a failover pair as well.I couldn't tell you off-hand what version we're running.

 

We only notice the issue on our guest wireless SSID, which sees up to 12,000 unique clients at any given time. The subnet has capacity for 16,000. We're assuming the failover pair isn't able to maintain the shared database at a certain volume/frequency of requests and simply stops responding.

 

For example, I have a log showing that the main recipient for requests receives DHCPDISCOVER from a client and no other logs relating to the client device show up on that server. On the failover, there are logs for that client showing that this server is trying repeatedly to defer to the unresponsive main. The client may/or may not receive an IP address and get connected to our network. Packet captures off the servers provide more detail to support this notion.

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