[plug] OT: Pool of IPs for testing load-balanced connections

[Adrian Woodley]

Having worked at an ISP, I know allow about "High Availability" and the 
likelihood of any given IP being actually available, especially when 
accessed off-net. :P

The way the load-balancing works, it sets a static route for the target 
IP via the gateway being tested. Traffic for this test IP will always be 
directed out that gateway, even when other connections are available or 
the gateway being tested is down. This means that a common/important IP 
can't be used (ie google.com's A record).

Because each router connected to the LINC will be doing its own load 
balancing, with its own static routes for the test IPs, each router will 
need a unique IP to test against.

For example, there are two routers, A and B. Both use 203.0.178.191 to 
test for internet connectivity via the LINC. If router A is elected the 
default gateway for the LINC, it will still route all connections for 
203.0.178.191 back out via the LINC (static route). Test pings from 
router B will hit router A and loop until the TTL is hit. In this 
scenario, router B will never decide that the LINC gateway is available.

If routers A and B have unique test IPs for testing for Internet 
connectivity via the LINC, the test ping will hit the opposing router 
and be direct out its current gateway, thereby establishing the validity 
of the connection.

Adrian

Tim wrote:
> Universities. ISP ftp servers. Friends static ip's. Friends servers
> hosted somewhere?
>
> How does the pool work? Do you have a server on the net that can
> maintain the pool list itself, by testing for internet connections to
> these ip address and if they are working, then to keep them on the
> list, if they aren't then to drop them. And when these networks have
> internet access, they update the list off your server?
>
> Or better yet.... How about the root DNS servers? (Ducks from any
> flack headed my way about extra load and miss using the root DNS
> servers)
>
> Tim
>
> On Thu, Sep 3, 2009 at 11:01 AM, Adrian Woodley<Adrian at diskworld.com.au> wrote:
>   
>> G'day PLUGers,
>>
>> I've just about finished the new design for the networking of the various
>> mobile comms facilities at work. Each comms unit should have an Internet
>> connection, either via NextG or a satellite uplink.
>>
>> The new network design will allow any combination of comms facilities and
>> up-links to join the Local Inter-Network Connection (LINC) and share their
>> routing information.
>>
>> Once the facilities are networked, the device with the highest priority will
>> be elected the default gateway for all other devices. Additionally, each
>> facility, with its own Internet connection, will load-balance between its
>> connection and the elected gateway.
>>
>> The (minor) issue I'm facing is that for the load balancing to work, the
>> router (embedded system running pfSense) needs to be able to ping a (unique)
>> target out on the Internet. What I need is a pool of very stable IPs to test
>> against, say around two dozen.
>>
>> The targets must be IPs, rather than host-names, as until a ping is
>> successful there is no Internet connection and therefore no DNS.
>>
>> Any suggestions?
>>
>> Adrian
>> _______________________________________________
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>>
>>     
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