Transitioning Major Commercial Networks Between Providers?

Kalon asks: "I am the network manager for a large business park connecting to our countries largest telco/ISP. We've recently negotiated to move our Internet services to another major provider and I'm stuck with a problem: our range of IP addresses (8 Class C's) is half 'owned' and half 'leased' from of our current provider. With some 90 companies relying on our connection for continuous Internet uptime, how can I transition forward and reverse DNS services for those companies with websites/mailservers unlucky enough to be on leased addresses, and route mapping for those whole blocks I own? Considering I don't have APNIC membership, what tips do you have to speed or ease the transition, considering I have to deal with lumbering telcos who won't play nicely together, and 90 different companies all demanding Internet presence?"

Comments

Buy 4 more Class C

[lewiscr]

Buy 4 more Class C subnets, and transition the people on the leased subnets now.

Then when you move, its just a matter of updating the routing.

Of course, changing the subnet routes could be another problem. A lot of the big routers don't propigate routes for anything smaller than a /19 subnet. I could be wrong about the size, but a /24 is right out. If your 4 existing subnets are all together, you've got a /22, and that might just work. Getting the 8 subnets together for a /21 would be better.

Set the TTLs LOW

[netringer]

As you get close tot the cutover time, set the TTLs (Time to live) on every DNS record you can get your hands on to a very low value.

Any host that does a lookup can legally only cache the answer as long as the TTL time. After that it has to ask again. With a low value you get a lot more requests to the DNS servers, but the host requesting will know about the change quickly so it'll find your servers at the new address as it changes.

The value is in seconds. 3600 would be an hour.

DNS and NAT

[funky womble]

If you have use of the old addresses for a little while after the new addresses are available, maybe you could run a NAT box on the old addresses for a short while so that inbound traffic could be directed to the new addresses. Maybe something like this -

1. setup the NAT box
2. change IP addresses on a machine
3. add NAT rule to direct traffic to new address
4. if more_machines_to_move goto 2
5. beer/pizza/etc, you earned it (:

Or instead of using a NAT box like that, you could possibly put it in front of customer servers and/or routers, so they could keep the configuration with their old addresses for a while longer, giving you a little more breathing space (obviously you need to update DNS while you're doing that - you might find tinydns, part of the djbdns package, useful as it can control the TTLs, making it fairly easy to expire DNS records at a particular time and replace them with new ones).

I know an ISP that has been putting off renumbering for several years, I don't think their former transit providers are too happy about having part of their own netblocks announced at them :/

Think of it as a challenge and also proof that there are certain (fairy limited) circumstances where NAT doesn't completely suck!

been there...

[chrismcc@netus.com]

Hello...

I've done this. It isn't fun, but it's doable.

quick options
1: use two providers
you get to keep your address
you have redundancy

2: hire someone that has done this before

long solution:
get your own address from arin or suitable authority. with 90 companies connected, getting a /20, /19, or /18 should not be a problem

bring up second connection. establish BGP sessions with both providors announcing all (old and new) ip addresses.

plan on transitioning a few customers per day. I imagine most of your customers are 9-5ers. They are easy. Save the more critical ones to last as you'll have had a lot of practice.

Using DHCP on their side helps

Co-ordinate with the companies IT person. You update the routers/routes, and they update the DHCP server. Easiest done as they leave for the day.

do not do NAT in the routers. It will kill your performance.

The whole transition could take up to two or three months. Don't get in a hurry. Do it right the first time.

Setup DNS servers on both old and new ip address blocks.

Consider keeping the old connection (maybe at a lower bandwidth) for redundancy. or kill old provider connection.