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bridging multiple vlans across a T1 on a cisco 1921

flitcraft33
Level 1
Level 1

For reasons too complicated to describe (trust me, don't ask) I have two cisco 1921 routers with EHWICs wit  2 T1s back to back across two aggregateed fractional T1s.  This CANNOT BE CHANGED.

 

I have 3 vlan segments (4 if you count a native vlan, id 1, that is not otherwise used).  I have to bridge these vlans, because the same address space is used on each side. I have no DNS so cannot do the NAT thing. I have to bridge the vlans across the aggregated T1s. On one side the 1921 connects to an old 2950 on a trunked port. On the other side, the other 1921 connects to my 4506 on a trunked port.

 

I CANNOT get this working. I have tried bcp, subinterfaces, eveyrthing I can think. of. The routers see each other on the BVI IP addresses, but neither trunks succecsully to the attached switches or carries end to end traffic.

 

I have tried subinterfaces like below, and BCP with the vlan-range command. Nothing seems to work for me, BUT I have to get his going.

I was thinking some kind of q in q maybe?

 

CDP works across all the links. I can post configs if you think it will help, but all it will show is a non working trunk port config on the router. Like I said above, the T1 part works fine.

 

The VLANS I need are 1,10,100 and 108. VLAN 1 is the native vlan.

 

THanks for any help.

 

 

Dan Sichel

Ponderosa Telephone

 

 

 

 

2 Replies 2

Ryan Curry
Level 1
Level 1

Dan, sounds like you've got some fun a head of you.  Not sure if this is what you're looking for, but I found this that "might" do what you're looking for (though you'll probably need sub interfaces for the VLANs you have): http://www.cisco.com/c/en/us/support/docs/ip/layer-two-tunnel-protocol-l2tp/116266-configure-l2-00.html

Found an old but still supported bit of awesomeness thanks to TAC.

Here is the relevant part of the config.

controller T1 0/1/0
 cablelength long 0db
 channel-group 0 timeslots 1-18
!
controller T1 0/1/1
 cablelength long 0db
 channel-group 0 timeslots 1-18
!
!
!
!
!
!
!
bridge irb
!
!
!
!
interface Multilink1
 no ip address
 ip virtual-reassembly in
 no ip route-cache
 ppp multilink
 ppp multilink group 1
 bridge-group 1
!
interface Embedded-Service-Engine0/0
 no ip address
 no ip route-cache
 vlan-id dot1q 10
  exit-vlan-config
 !
 vlan-id dot1q 100
  exit-vlan-config
 !
 vlan-id dot1q 108
  exit-vlan-config
 !
 vlan-id dot1q 1
  exit-vlan-config
 !
 vlan-id dot1q 104
  exit-vlan-config
 !
!
interface GigabitEthernet0/0
 description $ETH-LAN$$ETH-SW-LAUNCH$$INTF-INFO-GE 0/0$
 no ip address
 duplex auto
 speed auto
 vlan-range dot1q 1 213
  bridge-group 1
  exit-vlan-config
 !
!
interface GigabitEthernet0/1
 ip address 10.5.0.3 255.255.255.0
 no ip route-cache
 duplex full
 speed 100
 

 

 

stupid simple works great.

 

Dan S.

Review Cisco Networking for a $25 gift card