On Fri, 13 Nov 2009 18:05:44 +0000 Mark Rogers mark@quarella.co.uk allegedly wrote:
I have just spent the afternoon trying to get my head around this one and failed.
A customer has been set up with a new ADSL account with the following IP addresses: 88.x.a.116/30 (routed IP range) 88.x.b.170 (static IP).
I need to configure the router to everything to a firewall that'll route traffic accordingly.
I can't even work out from this configuration how many usable external IP addresses this will give them?
(I can get the router connected with the static IP in a normal configuration without problem.)
PS: God bless my Ubuntu Live CD, the tools you have to manage without on Windows!
A slash 30 gives two usable addresses. I'm assuming that the static IP (88.x.b.170) is assigned to the external interface of the ADSL router (so they have one external address). This router must be setup for no NAT because they have been allocated two routeable addresses internally (88.x.a.117 and 88.x.a.118). In this case I guess that means that the router's internal address will be 88.x.a.117 which gives you 118 to allocate to a firewall (or other router) which can NAT an internal RFC1918 address block to give you the network you want. (Or of course you could just NAT at the ADSL router).
I guess it looks something like this
Outside--88.x.b.170[ROUTER]88.x.a.117---inside---88.x.a.118[ROUTER]192.168.x.x
Mick
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The text file for RFC 854 contains exactly 854 lines. Do you think there is any cosmic significance in this?
Douglas E Comer - Internetworking with TCP/IP Volume 1
http://www.ietf.org/rfc/rfc854.txt ---------------------------------------------------------------------