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Windows DHCP SYN

James Bond

James Bond

Diamond Member
If a Windows NIC requests a DHCP lease and doesn't get a response, how long until it sends out another SYN?

I had an instance just now where a router locked up. Hosts couldn't contact the DHCP server/gateway.

They fall back to 169.x.x.x.

Router comes back online. Hosts still unable to get to internet. IP still stuck at 169. When would the next DHCP SYN have come through?
 
James Bond said:
If a Windows NIC requests a DHCP lease and doesn't get a response, how long until it sends out another SYN?

I had an instance just now where a router locked up. Hosts couldn't contact the DHCP server/gateway.

They fall back to 169.x.x.x.

Router comes back online. Hosts still unable to get to internet. IP still stuck at 169. When would the next DHCP SYN have come through?
Click to expand...

The next time the network connection changes state, computer reboots or a user requests the change. (ie ipconfig /renew or ipconfig /release ipconfig /renew)
 
Are you asking how many times it will retry and what the timers are for that before it fails? It sounds like you're asking "after it's already failed DHCP all together when is the next time it will try without any change in the NIC link"

If so I think it's like 5 minutes but I can't remember.

-edit-
Now that I think about it, Imagoon is right. It won't try again until you "kick" the IP stack with what he mentioned.
 
Last edited:
Good to know. I assumed that there was a "retry timer", but apparently not.

Thanks guys!

But also, as Spidey mentioned, how many times will it attempt before it gives up? ie how many SYN will be sent until it gives up without receiving an ACK?
 
Good link. I'm slightly confused on his explanation at one part:

Thus, if we consider the first DISCOVER packet at 0 seconds, then 4 packets are sent out as:

0th second - 1st packet with 5 sec timeout
5th second - 2nd packet with 7 sec timeout
12th sec: 3rd packet with 15 sec timeout
27th sec: 4th packet with 32 sec timeout
The above 4 packets with a final timeout of about 1 minute may be considered as a “set” for the purpose of this discussion.

In Windows Vista: One such set is sent out every 5 minutes as can be seen above. After one set, the DHCP client sleeps for 275 seconds or over 4.5 minutes.

In Windows XP: The first 2 sets are sent one after another, after which one set is sent once every 5 minutes (approximately).
Click to expand...

From what I understood above: In Vista, it runs through the set once, then sleeps for 275 seconds. In XP, it runs through the set twice, then sleep for 275 seconds. But then, he says "after which, one set is sent out once every 5 minutes". It seems like that would conflict with the 275 seconds?
 
James Bond said:
Good link. I'm slightly confused on his explanation at one part:



From what I understood above: In Vista, it runs through the set once, then sleeps for 275 seconds. In XP, it runs through the set twice, then sleep for 275 seconds. But then, he says "after which, one set is sent out once every 5 minutes". It seems like that would conflict with the 275 seconds?
Click to expand...

Well 275 seconds is 'approximately' 5 minutes.
 
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