Can a Cisco 877 Router be configured for BT UK Multi IP address?

Posted on 2010-09-09
Medium Priority
Last Modified: 2012-05-10
I am looking at a solution for a client who currently uses a BT 2 wire router with a single ip address, there is another customer in the building now expanding and wanting to use their own mail server.

When i configure a BT 2 wire for multi ip address you have to do this via address allocation and this makes the router transparent, i would like to know if the cisco can hadle 5 ip addresses from BT and if i can use basic routing as:

ip nat inside source static tcp <local> 25 <public ip> 25 route-map SDM_RMAP_1 extendable

You may ask why i dont just use the BT box, but the client does some work for the other tenent in the building so i will have to configure vlans with access between them.

Any advice before i commit to a solution would be great.
Question by:smartit_richard
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LVL 34

Expert Comment

by:Istvan Kalmar
ID: 33637031

it isn't working you must config only ona address to translate:

ip nat inside source static tcp <local> 25 <public ip> 25  extendable
ip nat inside source static tcp <lacal2> 25 <public ip_2> 25  extendable

Author Comment

ID: 33637190
This was my plan, but BT in the UK is very odd with IP address allocation, do you think this will work?

i guess i must allow the router to negotiate the initial WAN ip then setup NAT as:

ip nat inside source static tcp <local> 25 <public ip> 25  extendable
ip nat inside source static tcp <lacal2> 25 <public ip_2> 25  extendable

has this been tested with BT?
LVL 34

Accepted Solution

Istvan Kalmar earned 1500 total points
ID: 33637337
If BT routed to your router the new IP addess it is working!
I am not tested with BT, but I tested with Deutche Telecom!

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Author Closing Comment

ID: 33637379
I am happy with the solution and will recommend this to my customer. if anyone feels this will not work please advise.

Expert Comment

ID: 33637766
BT in the UK do allocate WAN IP addresses very strangely....

If you have multiple static IP addresses, then they allocate the "outside" router address dynamically and then route your multiple IP addresses to that dynamic one - confusing, eh?

Typically, I would allocate on of the subnet to the router (add as a loopback on the cisco), so the router can be managed from my network management centre on the outside. The other statically allocated addresses can be simply added to the nat statement similar to your original post. The router knows how to deal with these for you. What do you have in the route map? You may not need it to be that complicated...

Author Comment

ID: 33638298
I completly understand what you are saying in your post so i just use the NAT statements to inform of traffic, good news i guess, router management from the outside is a no no for me anyway as we would only ever manage from inside.

As for the route map this is all sorted i just has to get my head around BT and its odd manors..

Thank you for your help.

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