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Dumb networking question

Old 19th Sep 2017, 11:46
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Dumb networking question

At one end of the office network (wired) is a Virgin cable internet connection and router (which is our main permanent internet connection - and [touch wood] very stable).

We also have (at the other end geographically) a Talk Talk ADSL connection and router.

While doing some cable tidying (primarily involving our little PBX unit and a herd of cordless base stations which work off it - all of which now live in a cupboard) a thought came to me ....

In the event of a Virgin failure (stop giggling at the back) I could drop a network cable into the hub under the desk at that end of the office and we would have some level of internet access.

BUT - if I was to simply plug it in now (with a fully operational Virgin still connected) what happens:

1) Does everything become confused and/or simply blow up (two IP addresses / points of presence etc) ?

2) Does technology simply sort it out and carry on as if nothing has happened (perhaps using the best choice available - almost certainly Virgin) and effectively 'hot swap' if the other falls over

3) Do I have to do 'something technical' to achieve 2 above ?
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Old 19th Sep 2017, 11:57
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It appears (bit of googling) the answer lies in no 3

- just for clarity - the virgin connection copes happily with 99.99% of life, but was just wandering whether I could leave the Talk Talk cable plugged for the rare (hopefully) wobble with Virgin.
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Old 19th Sep 2017, 14:33
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I was toying with getting a 2nd broadband connection in my home to ensure that I always have a connection, so I gave this some thought.

At its simplest, you have router A with internal address of and router B with address of Router A is the DHCP server, with DHCP service switched off on router B - assuming that you are using DHCP.

Your clients are all on the same subnet as the 2 routers, but in normal operation their default gateway is, being the better connection. In the event that router A or its upstream connection fails, you would switch A off, enable DHCP on router B and run a DHCP release / renew (IPCONFIG /release, IPCONFIG /renew in the Windows world.

Your clients are now connecting to router B for their internet connection.

Of course you can use fixed IP addresses, in which case you just have to change the default gateway manually on each client.

If you want to use both connections, you can use non-overlapping DHCP scopes, still within the same subnet, or use fixed IP addresses to achieve the same effect, such that some devices use router A and some use router B, using one of the above mechanisms to cater for failure.

Using DHCP in this way is a bit hit & miss as to which device connects to which router, but for me I would use fixed IP addresses for all PCs, and DHCP for phones & tablets.

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Old 20th Sep 2017, 02:11
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Life was easier before computers.
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Old 20th Sep 2017, 02:28
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Mobile devices such as iPhones and tablets have the ability to hot swap between wifi networks that they have previously been granted access to. Desktop systems generally need to be manually switched between networks if the primary router fails.

There are security issues inherent in not being aware at all times which network you are actually currently connected to. A strong unencrypted connection might be made to a router that was outside your home or office allowing third party access to your communications. This is a distinct possibilty in multiple occupancy buildings, where wired connections are always to be preferred in the interest of maintaining data security.
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Old 20th Sep 2017, 13:14
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I was toying with getting a 2nd broadband connection in my home to ensure that I always have a connection
That's devotion!
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Old 20th Sep 2017, 19:16
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That's devotion!
If you regularly work from home and rely on VPN connection, it's essential to have a solid connection whenever you need it. If the internet connection is down, I can't work effectively, hence the consideration. I'm happy to balance the commuting savings and improved work/life balance against the cost of a 2nd internet connection.

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Old 20th Sep 2017, 19:49
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We have a full blown office (2 + 3 staff , soon to become 2 + 5 staff) at home, so mixed considerations.

'Always on' internet access is pretty important to us - but so is security (we work in financial services).

For now, simply plugging in the Talk Talk ADSL should Virgin cable fall over ('touch wood' - not happened for a considerable period of time) is probably satisafctory.

But greatly appreciate the input and will go ann 'read up' some more
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Old 28th Sep 2017, 18:58
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Option number x is a Dual WAN Router. This is a single device that you can have 2 different ISP connections and this will give you a Failover if one ISP goes down. It doesn't help if the phone exchange is the culprit that has the issue as both ISPs will connect to you through the same exchange. It will also require 2 Modems (one for each ISP) but the Dual WAN Router will handle DHCP, DNS and anything else you may need configured.

Read the link I have left I the first sentence as that explains it better than I can while my present visitor Ian Somnia stays for an unwelcome visit.

Google Dual WAN Routers. This may help you research this option further. This type of router is still a single point of failure if the device fails but it does save having to configure 2 different routers that you would need for 2 different ISP connections.
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Old 29th Sep 2017, 13:21
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Thanks Biggles (and others) - will have a read up.

As sod's law would have it, Virgin network failed on Wednesday afternoon - I cold swapped to the ADSL connection and what a pain that was - as was swapping back next morning.

Problem with the dual router is that the inbound connections are at opposite ends of the building/network but that shouldn't be unsurmountable.

Looks like my weekend project !!
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Old 3rd Oct 2017, 08:45
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inbound connections are at opposite ends of the building
If you ensure that you are using twisted pair cables then internal extensions are quite viable for telephone line based ADSL. It is a twisted pair to the exchange which may be a mile away, a few yards more are not going to make much difference in most cases.

One thing I did not see mentioned is that if you do go the dual line route for reliability it is essential to ensure that you have a means of detecting a line failure before both of them fail. You could for example schedule a manual cut-over every month or few in the worst case. Ideally automatic reporting should be used but that may be beyond your economic implementation.

A dual port router may provide some tools for this. If both lines are active then a special static route may allow you to route test pings out of the backup line.
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Old 8th Oct 2017, 17:50
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Originally Posted by ExSp33db1rd View Post
Life was easier before computers.
And before the creation of the social network too :-)
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