How to glue and aggregate two broadband connections

Posted on 2006-04-21
Last Modified: 2013-12-29
I have a cable broadband connection and just recently added a DSL broadband connection for home use.  I work at home and need the back up connection in the event one connection goes down.  I also have two Linksys routers connected to each of the connections.  Cable (faster line) is connected to the Linksys SRX 200 and the DSL is connected to the Linksys 802.11b Wireless 4port switch/router.

Aside from buying new expensive dual wan hardware - is there a way to connect my pc to both of these routers/broadband connections simultaneously?  The ideal solution would allow for aggregation of both connections in addition to fail over.

I also have a corporate laptop that connects to my employers network via the Nortel Contivity VPN software, which I've heard is a problem for most dual wan routers in regard to load balancing with VPN connections.

Both PCs have a wireless and wired ethernet connection - two wan cards.
Question by:samlaird
    LVL 4

    Assisted Solution

    Configure your routers with a Different IP.
        Cable                            DSL
       Router1                      Router2    
          !                                   !

    not with DHCP but with static IP for not hacing conflicts..

    When 1 connection goes down just change the gateway and you're set..

    hope it helps

    LVL 44

    Assisted Solution

    "is there a way to connect my pc to both of these routers/broadband connections simultaneously? "
    The answer is NO -- windows will only see ONE route to the internet, it is incapable of multiplexing two or more different internet routes, becuse your IP must resolve to a single IP, and if you have 2 routes, that violates the internet rule of one IP number per internet node.  The answer is NO, sorry, no two routes.
    LVL 2

    Assisted Solution

    Hi samlaird,

    If you have two DSL connections you can "bond" them.

    This involves either having your ISP configure their
    DSLAM upstream to accept the bonded DSL connections
    or to utilize MLPP on your multiplex router and have your
    ISP accept the MLPP on their DSLAM

    The routing has to be done "below" the IP level
    since scrathcyboy is correct in saying that the router wouldn't
    know where to deliver a packet to if there were multiple
    routes for it.

    Not a lot of ISP's offer this, but there are some that will.

    Good Luck!
    LVL 3

    Assisted Solution

    You achieve failover and load balancing by defining static routes in the routers. Hook up the PC and the routers as desscribed by CKWT. Set the default gateway in the PC to (router1). Now define in router1 a static route for the IP address of employer and set the gateway of that route to the IP address of router2. Set the metric to say 50. Add another route in router1 for your employers IP address and set the gateway of that route to whatever the default gateway of router1 is. If you set the metric for that rule also to 50, then you have achieved load balancing. Half the packets will go out via your DSL connection, the other half will go out via the cable connection.
    If you give the second route  a higher metric then more packets will go via router2: eg of you set the metric of the second route to 100 then there will be twice as much packets go via router2's ISP then via router1's ISP. In order to maximize the traffic, you could optimize your load distribution this way.

    This load balancing would work fine if..... you would not use NAT. With Network Address Translation the picture changes a bit in a sense that a server will see different source IP addresses for packets of the same session. Chances are that this will greatly confuse any server, esp if you are sending transaction or session based traffic, eg TCP based or VPN. You employers VPN server will see a login request coming in from router1 and then subsequent data from router2, or vice versa. The packets from the router that did not pass the login request may be rejected. This explains what you heard about the issue with VPN traffic.

    So, what you may want to do is settle for failover. Do the same as above, but set the metric of the first route to 1 and of the second route to 1000 or so. This will cause 99.9% of the packets to go out via router2. The 0.1% packets that fail when they go out via router1 will be retried and they will go out via the router2 then to. If router2 fails then all packets will go out via router1's ISP.
    Note that this set up will do a faiover in case the ISP connection of router2 fails, it does not protect you from failure of router1. In that case you would still need to change the default gateway in the pc from the IP address of router1 to the IP address of router2.

    LVL 57

    Assisted Solution

    You can't aggregate your connections as is.  No equipment on this earth will allow you to do it, without working with both ISP's.

    When using a VPN the "outside tunnel" IP address from your side must be the same.  Because of the way cable and DSL work, you will get a differnet outside IP address depending on which path you take.  If, big if, you were to happen to have static IP address from one, or both, providers, because each ISP is allocating you a unique IP the other ISP will reject the IP address that is not "theirs".  That is lets say cable provided you with x.x.200.5 and DSL provided you with x.x.100.23, when you try to go out using x.x.200.5 on the DSL link, they will say, "Hey this isn't one of mine." and drop it.

    You would need to get a static IP address from one of the ISP's and then get both ISP's to allow for the other one to route that address through (both inbound and outbound to them and from them) their networks.

    Very seldom if ever are they going to do this for the home account.  For businesses they will, but I am not sure about for Cable/DSL type accounts.  I have only encoutred this with dedicated phone circuts (T1's and the such).

    hfern is sort of correct on the dual default routes.  The problem is the detection of a failed route is based on the not getting a response to an ARP request.  So if the cable modem is up, but the cable connection is down, the cable modem will respond to an arp and thus you will not be able to tell that is is down.  Now some cable modems work "unusal" and are more of a ethernet to coax converter.  I am not sure what you would see if the cable side was down and the modem was up.  You may want to experiment by disconnecting the coax from your cable modem and see what happens on the PC side.

    What you would need to do is seutp a script that "talks" to something beyond the cable modem, say ping some IP address o the Internet that allows you to ping and you hope is always up.  If there is no response to the ping then change the default route to your other router.
    LVL 1

    Author Comment

    All of this confirms my suspicion - in that it is really not a viable option to use both.  

    Leaving the VPN situation aside (I will manage that connection manually), would one of the Dual Wan routers work well for normal internet traffic?  If so, does anyone have a reommendation on which of dual wan routers is the best?

    I would still like to use my SRX 200 wireless router, and I've been told that I can connect that router into the dual wan router - are there any issues with that?
    LVL 57

    Expert Comment

    That should work:

                                           |---> T1 #1
       SRX200 <---> Router <-
                                           |---> T1 #2

    I would suggest that you contact your ISP and see what routers they would suggest.  That way if you have problems, they can help.
    LVL 4

    Accepted Solution


    For around 160 (usd) retail, or $120 from the right reseller you get

    4 Gigabit LAN ports
    Dual WAN Ports configurable for load-balancing or just plain redundancy
    ( I'd be really curious what this could do with 2 Fiber connections a'la Verizons FIOS!!)
    And is endpoint-to-endpoint OR client based VPN ready.
    Before all the Netgear haters strike me down, this is part of their ProSafe line which are much higher grade than than their plastic home counterparts. My company has installed this particular model for clients in the double-digits and have had problem 0 for over 9 months.

    Configured in load-balancing mode you will enjoy a theoretical combined bandwith for your Upload and Download, internet traffic will SCREAM.

    If your WL router doesn't have the capability in operating as an Access Point only, write back and I'll tell you a cool little trick involving static routes that will accomplish said objective.
    LVL 4

    Expert Comment

    This article seems to explain the situation in clear, simple terms.,1759,1641359,00.asp

    Here's their cheapest suggestion:

    The XC-DPG502 Twin WAN Router ($300 street) has two Ethernet WAN ports, each of which is configured independently and can be connected to a cable or DSL modem, a T1 line, or a wireless Internet connection. Each can also be designated for either full-time use or as a backup should the other go down. If both WAN interfaces are used simultaneously, traffic can be balanced between them by packets or bytes or by number of sessions.

    The XC-DPG502 does only downstream (client) load balancing, which is fine for offices that do not run servers. If you need upstream load balancing as well, Xincom offers an enhanced model, the XC-DPG602 ($800), which adds a DNS server. The XC-DPG602 also requires more RAM and flash memory. (Xincom Corp.,
    LVL 1

    Author Comment

    Thanks everyone - all of your answers put me in the right direction.  I thought there was a way to split the points, which was my intent, but I wasn't given that option this time.

    Thanks again
    LVL 1

    Author Comment

    Thanks everyone - I was able to get the moderator to undo my error and then I was able to split the points.  

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