ISP switching

[ltellis026]

Hello all, 

My network engineer went down with Covid and I have been left trying to finish a series of ISP swaps that were on his plate by the end of the week.  These are 4221 routers and admittedly I haven't done this sort of thing in years. In fact I will probably farm the rest of these out if I can....but the one in front of me now is flat out down so can anyone take mercy on a poor guy down on his look and hasnt touched a router in years and walk me through changing the GW, DNS, and probably modifying a static route since my sh run is also showing a static route that would be looking at the old ISP as well?

[Richard Burts]

We have a general description but very little useful detail to help us understand your situation. A good starting point would be to post the current running config (after disguising sensitive information such as passwords and Public IP). 

I do have a couple of questions and comments:

- changing DNS should not be difficult. Has the new ISP provided addresses to use for DNS?

- you say this router is flat out down. Can you help us understand this? Is it that the old ISP no longer is providing service to that router? Is it some other issue?

- if that router is flat out down, do you have access to that router?

- changing the gateway and changing the static route are likely the same task? What kind of information did the new ISP provide?

[balaji.bandi]

as i understand high level you looking swap the ISP from OLD to new.

to help better :

1. Login to Router issue command - # show run ( remove any confidential information and post here)

2. Explain what is the old ISP IP address

3. what is the new ISP IP address allocated to you

4. give the information what port the ISP Link connected, are you replacing old Link with new Link ? what Delivery (ethernet or fibre ?)

5. Do you have small diagram of network for us to digest and suggest anything we can best.

Note : always keep the backup working config out of the box, in case required to roll back to old config.

Do simple changes 1 at a time and test it.

since you doing after long time, make more maintenance window, also you need to Line up ISP Side if you see any issue.

offline test, connect  PC to new ISP make sure it working (if this is ethernet delivery)