dhclient: lease renewal woes

Mr Dash Four mr.dash.four at googlemail.com
Sun Sep 9 13:54:30 UTC 2012

> Your wording is a bit strong. What you call "mindless" is in fact 
> there for a good engineering reason and makes renewals work very 
> nicely for any properly engineered network.
It is "mindless" when a piece of software tries to renew its lease and 
these attempts are taking place non-stop for 3 days (yes, that's right - 
three days!). That is what I consider "mindless" and unreasonable.

> You should not blame the software for your ISP having a rubbish network.
I don't, but I expect that every decently written piece of software to 
have a "plan B" which could be deployed - swiftly - if "plan A" doesn't 
seem to work. That, evidently, isn't happening with dhclient.

> Incidentally, did you ever figure out why the client was not renewing 
> by broadcast at around 7/8 of the lease time which is what I assume 
> it's doing now ?
A couple of factors, one being that the server specified in the server 
ID given in the lease acknowledgement is not responding to direct 
requests, which is what dhclient was doing (instead of switching to 
either a broadcast or the dhcp agent giving the lease in the first place).

Another thing I've changed were these pre-defined periods - by default 
the lease renewal takes place when about 1/2 of the lease is still 
valid, and rebinds when 7/8 of that lease time has lapsed, give or take 
a randomly pre-selected interval. That may seem fine with short leases, 
but when the lease is long, the gap between 1/2 and 7/8 is quite a big 
one, so that is another thing I altered. It is all working now, so I am 
content with using dhclient for the time being. My "plan B" (yes, I do 
have one) was to switch to dhcpcd, if I couldn't fix the above problems.

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