Cisco 3925 Router-two interfaces with same subnet

[DAVID RICHWALSKI]

Hi....

I already know that the two interfaces g0/2 g0/1 cannot have an IP Address on the Same Subnet.

I know I have to do some sort of Bridge...but not sure how to do it.

And once I did..would there only be a single IP Address or @2

This is where i am confused..

Thx...

[MHM Cisco World]

Troubleshoot Bridge Virtual Interface and Bridge Domain Interface - Cisco

check this 
if not what you want then you must config VRF 

[Richard Burts]

We do not have much information about your environment and what you want to achieve. But it sounds like what you are looking for is Integrated Routing and Bridging. I believe that IRB is supported on 3900 routers. Using IRB you configure a bridge group on each physical interface, and configure a virtual interface (interface bvi x) which allows both physical interfaces to belong in the same subnet and to bridge traffic between the interfaces. In this implementation there is a single IP address (which is configured on interface bvi) which is used by the physical interfaces.

[Georg Pauwen]

Hello,

below is a sample config with the basic commands you need:

hostname R1
!
bridge irb
!
interface GigabitEthernet0/1
no ip address
no ip directed-broadcast
bridge-group 1
!
interface GigabitEthernet0/2
no ip address
no ip directed-broadcast
bridge-group 1
!
interface BVI1
ip address 192.168.1.1 255.255.255.0
!
bridge 1 protocol ieee
!
bridge 1 route ip

[Joseph W. Doherty]

The other posters have well answered your question but I wanted to insure you understand that this feature bridges its interfaces at L2.  If you're familiar with L3 switches, this is much like having interfaces in the same VLAN and using a SVI.

[DAVID RICHWALSKI]

Here is some information I should have given right away...my bad....

interface Loopback0
ip address 10.0.0.1 255.255.255.0

interface Embedded-Service-Engine0/0
ip unnumbered GigabitEthernet0/2
service-module ip address 192.168.0.51 255.255.255.0
service-module ip default-gateway 192.168.0.50
service-module enable

interface GigabitEthernet0/0...... is my WAN connection to the World...

interface GigabitEthernet0/1....... this is the one I wish to configure
no ip address

interface GigabitEthernet0/2......this is my LAN

I am gathering the various Docs that I can find...and along with you all have given me some direction to follow...i plan on taking this on in a couple of hours...

192.168.0.0 255.255.255.0  subnet

[DAVID RICHWALSKI]

Here is more information if it will help...........

Cisco IOS Software, C3900 Software (C3900-UNIVERSALK9-M), Version 15.7(3)M6, RELEASE SOFTWARE (fc1)

Cisco CISCO3925-CHASSIS (revision 1.0) with C3900-SPE100/K9 with 1573120K/261888K bytes of memory.
Processor board ID xxxxxxxx
3 Gigabit Ethernet interfaces
2 terminal lines
2 Virtual Private Network (VPN) Modules
1 cisco Embedded service engine(s)
1 cisco ISM Crypto Engine(s)
DRAM configuration is 72 bits wide with parity enabled.
255K bytes of non-volatile configuration memory.
250880K bytes of ATA System CompactFlash 0 (Read/Write)

[Richard Burts]

Thanks for the update. I am still not clear about what you are trying to achieve. Can you tell us what is connected on interfaces g0/1 and g0/2 and how you plan to use them?

[DAVID RICHWALSKI]

g0/0 to Cable Modem (INTERNET)

g0/1 is the interface wish to configure

g0/1 is my LAN

[M02@rt37 · Accepted solution]

Hello @DAVID RICHWALSKI 

Only 1 IP @ attached to the Bvi Interface. The BVi interface id is equal to the vlan id. The vlan is assigned to the Giga 0/1 and 0/2.

interface GigabitEthernet0/1
switchport mode access
switchport access vlan 10

interface GigabitEthernet0/2
switchport mode access
switchport access vlan 10

bridge domain 10
interface GigabitEthernet0/1
interface GigabitEthernet0/2

interface BVI10
ip address 192.168.1.1 255.255.255.0

Enable bridge domain with the command: bridge irb