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New Member

3550 fallback bridge

Hi all,

I tested the fallback bridge in 3550 but not work.the following is the diagram:

3550--------R1

.........|____R2

In 3550, f0/1 is connected to R1, f0/2 is connected to R2.

I set the ip of the R1 to 192.192.192.192/24, the ip of R2 to 192.192.192.193/24. I also added the command to 3550:

bridge 1 protocol vlan-bridge

int f0/1

no switchport

no ip address

bridge-group 1

no shut

int f0/2

no switchport

no ip address

bridge-group 1

no shut

But I can not ping R2 from R1 and also in R1 I can not ping R2. use "debug ip packet" command in R1 , there is an encapsulation fail. In 3550 I use "show bridge 1" command and see the f0/1 and f0/2 is in "forward" status. But I think R1 can reach R2 because fallback bridge can bridge the frames that the switch can not route and the non-routed frame.Where did I do wrong? Can anybody tell me? Thank You!

Best Regards

Teru Lei

3 REPLIES
New Member

Re: 3550 fallback bridge

am having the same problem. It seems that the way fallback bridging works is different from bridge-group function in router. I was searching the 3550 config guide and found this line in Configuring network security section: (

http://www.cisco.com/en/US/customer/products/hw/switches/ps646/products_configuration_guide_chapter09186a00800c9fe8.html )(search for keyword "non-arp").

"Only non-IP, non-ARP packets can be fallback-bridged."

So I guess that because arp packets can not be fallback-bridged, when you do a ping, arp packets are not forwarded to other bridge ports and you will get an encapsulation fail error.

New Member

Re: 3550 fallback bridge

Hi,

Thank You for your reply. So I also think fallback-bridge use different technique. Did you try to use "arp" command to specify the mac and ip mapping to test? Thank You!

Best Regards

Teru Lei

New Member

Re: 3550 fallback bridge

You may want to recheck your routing configuration. You can successfully bridge non-ip (I've not work with fallback bridging) but not be successfull with routing. Are you performing dynamic routing or static? You should configure another router port (no switchport) or a L3 VLAN utilizing another unique subnet on each 3550 in addition to your current subnet configuration and test IP routing once again. Make sure to configure static routes on each 3550 or utilize dynamic routing. In fact, it might be wise to test IP routing with various subnets first prior to testing fallback bridging. Good luck!

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