IP address changing; any sendmail issues?

[Thomas Schulz]

In article <8F4DEC8C3shivawellcom at 207.126.101.100>,
Kenneth Porter <shiva at well.com> wrote:
>kirsch at rge.com (Mathew Kirsch) wrote in <8hosg2$1f48$2 at info.rge.com>:
>
>>Kenneth Porter <shiva at well.com> wrote:
>>> My ISP has informed me that my IP address will be changing at the end
>>> of the summer, due to a dispute between two address block holders (for
>>> 170.1.0.0). They will be issuing me a new address soon. I expect that
>>> I can deal with this by using both addresses on the interface
>>> temporarily, then getting the DNS record changed, wait a week for the
>>> old address to retire out of the DNS caches, then retiring the old
>>> address. Anything I need to worry about wrt sendmail? (The primary use
>>> of the box is as a mail hub.)
>>
>>As long as you are allowed to use both addresses during the transition
>>period, and your ISP will route the IP addresses for the transition,
>>there is no reason this shouldn't work reasonably well. It sure beats
>>not having mail service at all until everyone's DNS updates.
>
>It occurred to me that it might be tough for the ISP (RCN) to deploy the new 
>addresses alongside the old, as all their routers would have to be told about 
>this. I'm not sure just how capable the stuff is on their side. For example, my 
>system is on SDSL, and the interface is in a /4 subnet, with only itself, the 
>DSLAM, and the broadcast address sharing the subnet. If all commercial 
>customers are set up that way, and many need to have public names, then quite a 
>few routers are going to need temporary reconfiguration during the changeover.
>
>Any idea how others deal with sudden IP address changes?
>
>
As the time of the change approaches, start lowering your TTLs (time to
live).  That is: at 5 days before the change lower yor TTLs to less than
4 days, at 4 days before the change lower your TTLs to less than 3 days,
etc.  Just before the last day lower the TTLs to an hour or so.  A few
hours before the change, lower the TTLs to a few minutes.
After the change, put your TTLs back to their normal values.

Tom Schulz
schulz at adi.com