A DHCP Server story

A DHCP Server story

by Cyrus Lok on Saturday, April 3, 2010 at 2:05pm
I attempted to replicate my friend’s issue with Cat3550. Hence I configure dhcp server to supply ip addresses for 6 hosts. Actually I can limit to 2 hosts… in fact I do not have a lot of hosts to connect to a 24-port switch lol…

From a trouble ticket I came across one customer who claimed himself as an engineer and complained that there’s “something” wrong with his internet connection and he blamed it on his “ip address” lol.. wow…

So the tech support explained to him that ip address that his computer obtained was dynamically assigned by dhcp server. The customer was infuriated for some reason… (I found it really amazing that a person was flaring up when someone told him a fact… what kind of engineer that he claimed to be I do not know, but I am certainly sure he is not a network engineer).

The tech support was stressed by customer’s ignorant arguments saying that he kept getting the “same” ip address for several days…-_-” (Hmm.. what’s that got to do with his ambiguous claim about “something was wrong” with the internet?)

So the emotionally bullied tech support attempted to calm him down by requesting him to reboot his modem, rebooted several times customer’s computer still obtained the same ip address…gosh… I could feel how stress the tech support was when he was shouted by a customer who pretended that he knew “everything with the term engineer as the suffix” just because he was an engineer.

Well with all due respect, engineer is a very dynamic term… an electronic engineer who excels in his/her field does not necessary equates that he knows network engineering, it is totally unnecessary to point out to an innocent helpful tech support that he is an engineer and kept shouting at him. A paying customer who is frustrated does not equate he has the right to bully a tech support officer, moreover the tech support officer did not give up trying to help!

Anyway below is the dhcp stat received and sent by dhcp server.
3550-1#sh ip dhcp server stat
Memory usage 4969
Address pools 1
Database agents 0
Automatic bindings 1
Manual bindings 0
Expired bindings 0
Malformed messages 0

Message Received
BOOTREQUEST 0
DHCPDISCOVER 1
DHCPREQUEST 1
DHCPDECLINE 0
DHCPRELEASE 0
DHCPINFORM 0

Message Sent
BOOTREPLY 0
DHCPOFFER 1
DHCPACK 1
DHCPNAK 0

Before the lease expires PC will send dhcp request unicast to the dhcp to renew the lease, and dhcp server will respond back with dhcp ack unicast. As long as the lease is not expired PC’s ip address is still valid and will not change, as long as the lease is not expired ip address will still be valid even if DHCP server is down.

DHCP server will periodically send icmp echos to its own pool of ip addresses to ensure no duplication of ip addresses were assigned.

http://www.faqs.org/rfcs/rfc2131.html
(RFC 2131 read this if you have insomnia LOL)

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