Re: redundancy with Adsl modem

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Gáspár, my issue is an redundancy from ISP side. think that my two
connections with Internet is by line ADSL. so I'm thinking at the
contingency when an line adsl go down. I'm not regarding my connection
by ethernet cable between my modem ADSl and my firewall.

so....I have think how to monitor the adsl line as have ever comment before.


thanks.











Em 6 de janeiro de 2012 15:12, Gáspár Lajos <swifty@xxxxxxxxxxx> escreveu:
> Hi,
>
>
>>  yes, I need redundancy. when an line adsl come down all traffic go to
>> other line adsl. I couldn't have done this on linux machine. if you
>> has any how to about please post here.
>
>
> How do you want to do that???
>
> If you have two connections then you have two external IP-s...
> If one goes down then you can not simply use the other one...
>
> Just think about these steps:
>
> In normal connection:
>
> 1. a local host (A - 192.168.1.1) sends a packet from LAN to an external
> host (C - 8.8.8.8)
> 2. the firewall applies source NAT to the packet and sends it out as if it
> were coming from the firewall's first external IP (B1 - 1.1.1.1)
> 3. C sends back a reply to B1
> 4. B1 forwards it with destination NAT to A.
> 5. go to step 1. or close the connection
>
> If the line goes down between step 2 and step 3 then the reply packet will
> never get back to B1 and A (because the line is down) !!!
> If the line goes down after step 4 then you can send it out on the second
> extrenal IP (B2 - 2.2.2.2) but C will see it as a NEW connection !!!
>
> So I think that your request is impossible on IP level.
> However you can use a proxy or a mail server, etc. etc. etc.
>
> Swifty
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