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Configure Bridge mode on Cisco router for SDSL

Posted on 2010-09-20
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Last Modified: 2012-05-10
I'm configuring a SDSL Cisco 888 router that needs to become a modem bridge for the linux firewall.  Do I need to configure any connection details on the router?  I Have attached a script which doesn't seem to work!

service password-encryption
hostname xxxxx
enable secret xxxx
enable password xxxxx
line con 0
 password xxxx
line vty 0 4
 password xxxxx
no ip domain lookup
username xxxx privilege 15 password XXXX
interface ATM0
no ip address
no atm ilmi-keepalive
pvc 8/35
encapsulation aal5snap
dsl operating-mode auto
bridge-group 1
interface Vlan1
no ip address
bridge-group 1
bridge 1 protocol ieee
int f0
 no shut
int f1
 no shut
int f2
 no shut
int f3
 no shut
banner motd #
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Question by:jonperry2
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11 Comments
 
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Expert Comment

by:jmeggers
ID: 33725138
What version of code are you running?
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Author Comment

by:jonperry2
ID: 33730057
12.4
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Expert Comment

by:jmeggers
ID: 33730238
What interfaces connect to what? Is it only the Ethernet interfaces in use, or ATM on one side and Ethernet on the other?
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Expert Comment

by:jmeggers
ID: 33732999
I think you're on the right track, but I admit I'm kind of shooting in the dark here.  (It's been a long time since I did bridging.)  Most everything I see about bridging in the documentation refers to the wireless functionality.  Do you have a BVI interface configured?  I also think you probably need to explicitly assign physical interfaces to the bridge group.  It looks like you're assuming all switch ports are in VLAN 1 and are therefore part of bridge-group 1.  HTH,,,,
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Author Comment

by:jonperry2
ID: 33733195
Thanks,  it appears I can't assign Fasteth0 to the bridge group though with this IOS. Which might be a issue seeing as that's what the router attaches to...   I've added VLAN 1 to the bridge which I hope sorts this issue.  With the BVI interfaces do these need to be specified for all bridges?  
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Expert Comment

by:jmeggers
ID: 33733780
The BVI is the logical interface that allows you to assign an IP address but you may not need that for straight-through bridging.  I know you need it if you're trying to do Integrated Routing and Bridging (IRB) that allows you to route between bridge groups.  I'm surprised you can't add FE0 to the bridge group, can you add any of the other interfaces or do they all behave the same?

Unfortunately I don't see anything in the config guides I've been able to find that replicates your situation, and I don't have access to an 888 to play with it myself. If you don't have TAC support and can open a case on it, the next best thing I can suggest is to try the Cisco support forums on CCO at supportforums.cisco.com.
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Author Comment

by:jonperry2
ID: 33733946
Yep alas all interfaces  FE0-3  say they do not support bridging mode.  seriously find it hard to believe that I can't make bridge mode happen on a £400 router the rest of the os seems to support this though just these key interfaces.  Do you think the VLAN 1 being added to the bridging group will make these interfaces work.
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Expert Comment

by:jmeggers
ID: 33760522
I really don't know for sure.  Is there a reason it *must* bridge instead of route? I realize that probably seems like an easier configuration, but maybe not.
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Author Comment

by:jonperry2
ID: 33774387
No reasoin I guess for it not to router instead of bridge - anything to get it working really!
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Accepted Solution

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jmeggers earned 500 total points
ID: 33775645
Assuming you have a public IP on the outside of your firewall, moving to a routed design would mean moving that IP to the outside of the router, then using a private subnet between the firewall and the router.  You'll have to do NAT on the 888 but that's generally not difficult.  I'm assuming you're currently NATing on the firewall and your inside subnets are private.  Can you give me more information about what your topology looks like?  Also, I don't know Linux firewalls very well, can you route through yours without having to NAT the traffic?
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Author Closing Comment

by:jonperry2
ID: 33784417
Thanks for the help as I took your advice and moved away from the bridge method and used nat instead. Would love to know why cisco make it so hard to configure seemingly straight forward configurations in comparison to other vendors.  
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