Transparent mode between ISP and inside router

[Leo_Chan]

How to assign a BVI IP if public use 210.*.*. 64/30 255.255.255.252

[sludge3000]

Hi Leo_Chan,

You need to assign an IP address in the same network as the bridged networks (as the this is where the interface resides) but you do not have enough addresses to do that.
Is there any reason you need to bridge the interfaces and can't just configure the public IP on the external interface of the router in question?

Luke

[Leo_Chan]

Hi Luke,

As we are using 210.*.*.66  255.255.255.252 as our public IP,

can we set our BVI address as 210.*.*.68  255.255.255.252 ? (with Transparent mode in ASA 6618X

in front of our existing router and between ISP and the router.)

We want the existing router without changing anything to directly communicate with 210.*.*.64/30 255.255.255.252(ISP).

regards,

Leo_Chan

[Leo_Chan]

Hi Luke,

As we are using 210.*.*.66  255.255.255.252 as our public IP,

can we set our BVI address as 210.*.*.66  255.255.255.252 ? (with Transparent mode in ASA 6618X

in front of our existing router and between ISP and the router.)

We want the existing router without changing anything to directly communicate with 210.*.*.64/30 255.255.255.252(ISP).

regards,

Leo_Chan

[sludge3000]

Hi Leo,

Nope, that is not a valid IP subnet.

A /30 network (netmask 255.255.255.252) gives you two (2) useable I addresses, plus one network address and one broadcast address.

Example:

192.168.0.0/30

Network Address: 192.168.0.0

Broadcast Address: 192.168.0.3

Usable Address Range 192.168.0.1 - 192.168.0.2

As one address will be assigned to your ISPs device and one address will be assigned to your public interface, there are no additional addresses that you can assign for a BVI interface.

For additional resources for understanding IP subnetting, you can check out this Cisco article >> https://www.cisco.com/c/en/us/support/docs/ip/routing-information-protocol-rip/13788-3.html

Luke

[sludge3000]

If your ASA is in Transparent mode, the interfaces should automatically be bridged.

[Leo_Chan]

But we still need to assign a valid BVI ip to allow the bridged!

[sludge3000 · Accepted solution]

Then you need a larger IP block from your ISP or you need to re-design your deployment.