General networking question

Posted on 2011-05-06
Last Modified: 2012-05-11
I have an office with  T1 that come in.  They have a webserver.  Their T1 went doen for a few hours the other day and the owner decided that was unacceptable, so he called to get cable internet brought in.  He wants me to combine the two so if one goes down his website will still be up.  Is there a way to combine these two and what would I do on the nic for the webserver.  The only thing I can think of is run them both to the same switch but someone would have to change the settings on the external nic.  Anyway, I'm just looking for ideas.  Thanks
Question by:bergertime
    LVL 95

    Accepted Solution

    You need a Dual WAN Router - I good business class one like those from Fortigate would do nicely (I have one client running FiOS and Cable for redundancy).  Doing anything else would be messy and require manual intervention.  NOTE: you could have some challenges properly configuring e-mail delivery so that your messages aren't occasionally blocked as SPAM (my client had issues and I'm still not convinced they are all worked out).
    LVL 2

    Author Comment

    So, here's what I don't understand.  The guy surfing the web goes to my website, it hits global DNS, do I list 2 IP address there?  or how does it know that = or if it's down it needs to go to   I think I'm getting myself confused on this.
    LVL 3

    Expert Comment

    There are several problems to overcome for this to work:

    1.IP ranges - typically you'll get different IP addresses from each ISP. When you fall over you need inbound connections to arrive at the second set of IPs. For greatest resilience obtain a /24 "provider independent" IP block (or larger) and arrange for your (expensive) router to speak BGP4 with your ISPs.

    2.DNS entries - unless you have your own range of IPs (see #1 above) you need to have your DNS entries change on the fly. However many (broken) clients will ignore any TTLs that you publish and will continue trying to access the old IP range. The consensus view amongst DNS experts is that DNS is not the right way to achieve redundancy.

    3.Outbound traffic - your servers need to know which internet connection to send the return packets out of. This is potentially easier if you have both connections coming into a single router / firewall, but that then becomes a single point of failure too.

    There are some low cost devices out there though seems to be popular.
    LVL 95

    Expert Comment

    by:Lee W, MVP
    If this is an important web site, it should be hosted at a hosting provider - one that has redundant power, multiple redundant internet, and quality systems.

    If this is little more than a business card site, than you can host it yourself.  The problem with web hosting on multiple IPs is with DNS.  Typically, you need a "front  end" server that can load-balance the requests to multiple backend servers.  Your one server, using a dual-WAN router can handle this as the router is load balancing, but the DNS lookups will either ALWAYS provide the first server OR they will alternate (Round-Robin) amongst all known IPs for that name.

    So you could have:    #T1    #Cable

    and in Round-Robin DNS, the first time it's looked up, the DNS server hands out the T1 and the second time it hands out the cable, and the third time it's the T1, and the forth time it's the Cable...etc... problem here is that DNS is cached... so half the people trying to access your site when one line fails wouldn't be able to access it at all unless they could ensure their DNS servers cache expired.

    An alternative is to use    #T1    #Cable

    But this way, people have to know to try www1... and most people wouldn't.  This is why you shouldn't be hosting an important web site yourself.  The costs involved in ensuring access can be prohibitive.
    LVL 57

    Expert Comment

    saigasmith is on the path, but there are some other issues.

    #1) There is almost no way to get a provider independent /24 today.  The best you can do is get one of your providers to assign you a /24 out of their allocation, get your own AS number, and get both your providers to agree to do BGP and route the /24 assigned to you.

    2) DNS, as saigasmith states, won't work.  Not only do some client ignore TTL because they are broken, some people use caching DNS servers that specifically ignore TTL's.  That is why they say it take up to 72 hours for DNS changes to actually propagate through the whole Internet.

    3) This is really only needed if you have two different inbound IP address for the same server.

    Another option would be to get two Internet connection from the same ISP.  Say two T1's that terminate at two different local CO's and are connected to two different routers within your ISP's network.  The up side to this is that your ISP can handle the routing issue when one link goes down and they can also (within limits) load balance traffic between the two links.

    The down side is that if your ISP's internal network has problem, both of your links have problems.
    LVL 4

    Expert Comment

    you can't do it without using a single ISP that can setup this connection as a second route to the same IP... meaning you are not redundant any further than your ISP.

    If you try to get multiple providers to work together you will have more trouble than currently.

    Host your website somewhere with multiple internet connections like a hosting provider in a data center.

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