Can some one give me a good reason for this?

[Jay]

I have noticed a very odd thing, my pfSense router always get a totaly mad external IP from ISPs

eg

O2, use their router I get a 94.xx.xx.xx, connect a PC to a bridged modem it gets a 94.xx.xx.xx IP plug pfSense in and it gets a 188.xx.xx.xx IP

VM, plug a router in and it gets an 84.xx.xx.xx IP plug in pfSense and it gets some odd IP as well.

Anyone got any guess as to why this is?

[peterb]

The IP address has to be the one handed down by the ISP's DHCP server! However that will depend on which network you are connected to. When I connect to the vodafone mobile network, I get an address in the 10..0.0.0/8 range, which is the public class A address space - handed down by the vodafone internal network. I am then connected to the wider public internet with a 212.xxx.yyy.zzz address, which is the internet facing address of the vodafone gateway. I wonder if that is what is happening with the pfsense router - it is picking up the private address space IP address (although the class B private address space is 172.168.yyy.zzz/12) What address does someone connecting to your network see?

[Jay]

They see the 188 address as well.

[peterb]

So the 188 is the public IP address - the other (I think) is effectively a NAT iddress given by the ISP's internal network.

[Jay]

Yes, possibly. I should put the old router back on and see what is the hop after the 94. address.

[Jay]

ok, I have some more info on this...

It gets more strange. If I use pfSense as my router I get put on "DUNDEE RESIDENTIAL DYNAMIC" ISP's IP Range, if I don't then I get the correct 94. ip range. I really can't get my head around it.

[burble]

10..0.0.0/8 range, which is the public class A address space?

10.0.0.0/8 is an RFC1918 address so it's private, not public.

the class B private address space is 172.168.yyy.zzz/12)

Not quite - 172.16.0.0/12.

[burble]

What MAC address(es) does the WAN port(s) of the pfsense router have? Did you clone the MAC from the O2 router?

[Jay]

no, I don't clone it but I have tried an ADSL modem and my PC to see if it was a MAC issue but the PC gets the same external IP as the O2 router gets so it can't be.

[burble]

I'm stumped then. I know O2 on their ADSL2+ packages at least do have some degree of IP address - MAC address matching as it threw me for a while why I was getting a different WAN IP address if I used the O2 router or a Cisco 877.

Maybe try cloning the MAC address anyway just to see what happens?

[Jay]

i'll get it a go later and see. Its odd that I would get an IP range way off what I should be getting though.

[burble]

Yeah, it's very strange. It isn't uncommon to get an IP from a totally different subnet but to get one from a block owned by another entity is extremely strange.

[peterb]

10.0.0.0/8 is an RFC1918 address so it's private, not public.



Not quite - 172.16.0.0/12.

Well it was 11:05 pm... - but thanks for pointing it out!