Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. And see here for current known issues.

New Member

Routing 2 isp's (T1 & wireless broadband) w/ 1841

Note: This is an existing thread in google groups, and I just copied and pasted the text. I really need some help with figuring this out, thanks.


I have a customer, they just got an Eschelon T1 in addition to their

existing wireless broadband from Sprint. I have been searching through

groups trying to find a definitive answer, but can't...I need to how

routing can be implimented using NAT over just the broadband.

They have a block of 8 from Eschelon, and the pix already nat/pat

internal net, but they want their traffic outbound (just from hosts;

all server traffic will go over the T1) to go over the wireless.

Obviously it doesn't need to be nat'd again over the T1, but how can I

get it out the broadband link? I'm pretty sure I need to nat because Sprint

won't take the Eschelon block over their network, and I'm just not

familiar enough with route-map statements to configure them myself.

Can I use a nat statement for just the interface of the PIX (which is

the pat int of the internal hosts) over the fa0/0 of the router?



Here is what someone has helped me with...

Thanks for the response. I will try this soon, but what I don't

understand is how either the pix or the router will know how to split

traffic out either end. The route statements don't look at source,

only destination, right? So the default route on the router is set for

Sprint, wouldn't all unknown traffic get pushed out that anyway,

regardless of the policy on the pix...? Again, I'm not too keen on,

nor a big fan of, the pix, so bear with me.

Also to clarify, they don't have a separate block from Sprint. Prior

to this install, it was a little Linksys router that was auto-assigned

an IP, and it was in a /24 block. I don't think that is correct, but

regardless they don't have a dedicated block to play with. They may

have one or two on the same subnet, but I need to double-check. So can

the policy still use an IP that isn't a "leased block" so to speak?

-----Original Message-----

On the 501, have two distinct nat (inside) policy numbers, one of

which matches the servers (-all- of their traffic is to go over the T1,

right?), and the other policy number for the other hosts.

Then have two distinct global (outside) statements, one for each

policy. On the global policy for the servers, have the outside IP be

one appropriate for the Eschelon. On the global policy for the other

hosts, have the outside IP be one appropriate for sprint wireless.

Then at the 1841 level, do *not* NAT the IPs. Do, however, add one or

more ip route statements to point both those IP ranges towards the

outside interface IP of the PIX.

As long as the packet gets to the outside of the PIX (because of the

'ip route') then the PIX will not care that the packet is or is not

part of the outside IP range: the PIX will look through its tables and

see that it has a translation for that IP and will put the packet

through as appropriate.

To emphasize and clarify: you may have an indefinite number of public

IP ranges being global'd (or static'd) to the outside of the PIX, and

as long as you route the packets to the PIX outside IP, the PIX will

handle them fine even though they are not in the interface subnet. The

PIX is happy to allow packets *through* that are not in the interface

subnet. The interface subnet is only important for when the PIX needs

to ARP the outside route destination, or when the PIX needs to *itself*

create traffic (e.g., you ping'd from a CLI, or you configured the PIX

to send RST packets), or the PIX needs to accept traffic itself (e.g.,

you ping the PIX -itself-, or you terminate a VPN tunnel at the PIX

interface.) But for traffic flowing through, the PIX doesn't care what

the IP range is as long as it has a translation.


Re: Routing 2 isp's (T1 & wireless broadband) w/ 1841

When NAT uses a route map to decide to create a translation entry, it will always create a "fully extended" translation entry. This translation entry will contain both the inside and outside (local and global) address entries and any TCP or UDP port information.Refer URL for informatin about configuring route-maps with NAT