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I need Help to configure an ubrvxr7246 (12.3 21a BC3).

IP routeur headend (X.X.X.1) Public address : I have no access on it.

IP UBR X.X.X.2 Public address (interface gigabit0/1)
IP BUNDLE 1 for interface cable3/0
X.X.Y.1 public address scope for host internet private address secondary scope for mta private address secondary scope for cm

I would like to ping (extended) X.X.X.1 routeur headend from and i can't.
Can someone explain me how do i proceed on the cmts to perform that ( the must see the X.X.X.1). (at this moment i can reach X.X.X.2)
Nat solution ? or other routing command ???

Thanks for you help


Do you have any route statements in the uBR config now?

You probably need a route statement on the upstream router (that you dont have no access to) that indicates that your network (you didn't show what masks are involved) is reachable through the public ip address on the uBR.

Something like the following:

ip route x.x.x.2 <-- where this is the Public address (interface gigabit0/1)

Note that I made up a mask above.


Thanks for the answer

Thanks for the answer mtntrailseeker

But i need your help again.

You re right with the submask

but when i crate this line
ip route x.x.x.2

the ubrs says :
%Invalid next hop address (it's this router)


Your not going to be able to

Your not going to be able to solve this problem with route statements unless you modify the other end (or get its owners to do so) and all points in between, your problem is not can you get traffic to the IP in question? but rather can the device in question get back to you. That is the part you do not control, without some help on the other end your only options are to use NAT or routeable IPs, or possible some kind of VPN.

That is the trick with non-routeable IPs they do not route on the internet, you can override this on a router by router basis but unless you can manually route it on all hops between your endpoints it is not going to work.

It seems that i have no help

It seems that i have no help on the other end . They ask me to do nat on CMTS.

How could you explain i can't ping X.X.X.1 and i can ping X.X.X.3 (dhcp server windows 2003) This 2 devices are in the same site on a same switch (no problem on the switch)

here are some options for

here are some options for you:

1. You can run NAT, though your whole CMTS will take a performance hit, for doing so. You can run an external nat router i.e. not the CMTS and route only the traffic you want to nat to it. This saves you the performance cost of nat routing on the CMTS and can easily be accomplished with a low cost cisco router such as a 2600 or 3600.

a basic Nat setup includes four lines of config in bold

interface gig 0/0
ip nat outside

interface bundle 1
ip nat inside

ip nat inside source list 1 interface GigabitEthernet0/0 overload
access-list 1 permit 1

2. The other option is to assign your MTAs routeable IPs.

Thks kwesibrunee This is the

Thks kwesibrunee

This is the same kind of Nat i did on UBR904.
When you say it will take a performance hit --> how can i appreciate the loss of perfrormance ?

And could you explain the second option ?


The performance hit will

The performance hit will depend on the amount of traffic your CMTS processes, when you turn Nat on that interface i.e. Bundle 1 and Gig0/0 each packet that passes through those interfaces will be inspected to see if they are a NAT packet. In the past when we used nat on a busy router, we took a 10-20% CPU processing hit just turning on NAT, there was also a processing hit for the actual NAT processing as well though for just MTAs to a certain network this particular processing hit is likely to be negligible.

Option 2 is to assign your MTAs routeable IP address via dhcp instead of a 10.x.x.x ip it would get an IP similar to what your customers PCs get this way any traffic from them will be routed normally over the internet.

thx kwesibrunee of course

thx kwesibrunee

of course ...
Sometimes i forget to think .

In this case, I am not ok with nat for voice. i have to find another solution cause it's not a good one

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