Split /25 for a new tenant, with no control over the ISP router possible?

[craig.corbett]

We currently have a /25 network. We’re getting a tenant in who’ll be sharing our connection, and we thought we’d split the /25 and share it.

Currently things look like this (IP subnet changed for the example):

80.34.55.128/25

With a configured outside route of 80.34.55.129

ISP – Switch – R1 80.34.55.128/25

What I’m aiming to achieve:

80.34.55.128/26
80.34.55.192/26

ISP Router– Switch – R1 80.34.55.128/26
                          |
                          |------R2 80.34.55.192/26

Would this be possible without having the ISP to make any changes on their managed router?

Any help / clarification, appreciated.

Thanks.

[craig.corbett]

In case it makes a difference, R1 and R2 will be Cisco ASA firewalls running NAT.

[Jeff Van Houten]

You're going to have to put the external interfaces of both r1 and r2 in the same /25 subnet.

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[Jeff Van Houten]

Actually, you can put r1 in a /26, but you're going to have to put r2 in a /25 in order to reach .129.

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