[TriLUG] Routing question
rleathers at americanri.com
Thu Apr 14 09:45:51 EDT 2011
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If the whole world used IPv6 you'd be set. You could do your part in
getting there by setting up IPv6 on the networks within your control.
Another possibility is to use some portion of the RFC1918 address space
on your private networks that is less likely to be in conflict. I find
that things in the class B allocation (172.16.0.0/12) are less often
used, so if you are not ready to make the leap to IPv6 then pick an
address space from this range for your private networks and you will
tend to avoid the problem you described.
Lastly, rely on 'order of specificity' in routing tables. Routing tables
always look for the most specific route to a destination. This means
that when we subnet we can have (EXAMPLE) one route to 192.168.1.0/24
and another route to 192.168.1.64/26. Both will work, but the hosts
.65-.126 will be reachable via whatever their next hop is while the rest
of the host addresses from 192.168.1.0 are avilable via a different next
hop. The more specific route always trumps a less specific one. Make
sense? Now be careful with this because certain dynamic routing
protocols don't like you to route subnets this way.
On 4/14/2011 8:52 AM, Brian McCullough wrote:
> I suspect that this is fairly easily solved, but I can't seem to get my head around this.
> I sometimes want to connect to a VPN from one of my machines ( usually a laptop ) while at, for instance, Panera's. Unfortunately, perhaps, the remote LAN uses 192.168 addresses, which sometimes conflict with the "home" address range given to the laptop.
> I am using PPTP from the laptop, and as long as the address ranges don't conflict, everything is fine.
> I tried setting a "Local IP" address on the PPP connection, and that seemed to work, at least as far as the address of that port was concerned. Unfortunately, of course, I still didn't understand how to set up the routing for that path, because, for instance, there is a machine local to the laptop that has the address 192.168.1.123 while one of the machines that I want to access on the remote LAN has the address 192.168.1.123.
> I don't think that I can reset the default route so that ALL of the traffic goes through the tunnel -- Internet traffic, for instance, would still travel through the "local" network, not the remote one.
> Knowing this group, I am sure that there are several someones who know exactly how to cure this problem.
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