07-26-2012 09:11 AM - edited 03-07-2019 08:00 AM
Hello everyone,
I have a design hurdle that I cannot seem to cross. I have two sites and I need the same VLAN to span both sites. I have accomplished this using L2TP but my issue is that I can no longer assign a gateway for this VLAN on the router. The 2 routers are 2821's and are connected with a dedicated fiber run.
Does anyone have a recommendation for how this could be accomplished? It would be great if I could have the same gateway at both sites by leveraging some sort of bridged interface (BVI so I've heard) but I am at a loss as to where I should start with this. Also, this is not the only VLAN that needs to traverse the link.
Any suggestions?
Thanks for your time!
07-26-2012 09:57 AM
Hello Terry,
in short IRB (BVI) works well if only one vlan has to be extended over the WAN link
Has no C2821 a free LAN interface ?
I guess the answer is negative. If one router would have a free LAN interface it would be enough to connect it to the same LAN switch. On the switch side both ports are configured as trunk ports carrying the set of Vlans V1-Vn that need to be extended over the routed network by L2TPv3.
On the router side one interface would have routed subinterfaces to provide default gateways to V1-Vn corresponding IP subnets. The other interface would have subinterfaces configured for L2TPV3 vlan based subinterfaces.
This is relative easy.
Now the issue is if no C2821 has an additional LAN interface to connect to local LAN switch.
IF the LAN switch has an unused optical port you could do the following:
Create a Vlan to represent the WAN link.
Example Vlan 990
the optical port to which the WAN link is connected is configured as access port in Vlan 990.
The router port is connected to the LAN switch either optically or by RJ-45 ( assuming you can choice the media-type on router interface).
The LAN switch port connected to the router port is configured as a trunk carrying the following Vlans:
V1-Vn + 990
on router side the current configuration of the WAN link is moved to subinterface 990 associated to vlan-id 990.
On the router vlan subinterfaces for Vlans V1-Vn can be created as needed.
This work needs to be done on a single site only
So the suggestion is to rearrange physical links so that both C2821 LAN interfaces are connected to the LAN Switch ( I assume there is a LAN switch in each site) and to convert the interface used only for WAN so that it has N+1 subinterfaces to provide the intersite link and the L3 def GWs to the extended Vlans.
Hope to help
Giuseppe
08-10-2012 09:09 AM
Here's the current setup:
GEORGIA TENNESSEE
VLAN101 ~> G0/0 (xconnect) ~> G0/0/0 (fiber) ~> Carrier (fiber) ~> G0/1 (xconnect) ~> G0/0 ~> VLAN101
The L2TP tunnel is up on both sides. Georgia is sending and Tennessee is receiving :
GEORGIA
Session id 418244970 is up, logical session id 32788, tunnel id 172807082
Remote session id is 11334, remote tunnel id 51199
Locally initiated session
Unique ID is 12
Session Layer 2 circuit, type is Ethernet Vlan, name is GigabitEthernet0/0.101:101
Session vcid is 302
Circuit state is UP
Local circuit state is UP
Remote circuit state is UP
Call serial number is 379500302
Remote tunnel name is
Internet address is x.x.x.x
Local tunnel name is
Internet address is x.x.x.x
IP protocol 115
Session is L2TP signaled
Session state is established, time since change 2d15h
447 Packets sent, 0 received
44804 Bytes sent, 0 received
Last clearing of counters never
Counters, ignoring last clear:
447 Packets sent, 0 received
44804 Bytes sent, 0 received
Receive packets dropped:
out-of-order: 0
other: 0
total: 0
Send packets dropped:
exceeded session MTU: 0
other: 0
total: 0
DF bit off, ToS reflect disabled, ToS value 0, TTL value 255
Sending UDP checksums are disabled
Received UDP checksums are verified
No session cookie information available
FS cached header information:
encap size = 24 bytes
45000014 00000000 ff73b676 010101fe
01010101 00002c46
Sequencing is off
Conditional debugging is disabled
SSM switch id is 4101, SSM segment id is 8203
TENNESSEE
Session id 11334 is up, tunnel id 51199
Call serial number is 379500302
Remote tunnel name is
Internet address is x.x.x.x
Session is L2TP signalled
Session state is established, time since change 2d15h
0 Packets sent, 446 received
0 Bytes sent, 44643 received
Last clearing of "show vpdn" counters never
Receive packets dropped:
out-of-order: 0
total: 0
Send packets dropped:
exceeded session MTU: 0
total: 0
Session vcid is 302
Session Layer 2 circuit, type is Ethernet Vlan, name is GigabitEthernet0/1.101:101
Circuit state is UP
Remote session id is 418244970, remote tunnel id 172807082
DF bit off, ToS reflect disabled, ToS value 0, TTL value 255
No session cookie information available
UDP checksums are disabled
SSS switching enabled
Sequencing is off
Unique ID is 669
When I assign an IP to a host in the Georgia side, it cannot ping the gateway on the other side of the L2TP tunnel. It seems that I'm only getting one-way traffic. Could this be due to a routing issue on the Tennessee side? We are currently using OSPF for route distribution of this network on the Tennessee router and are advertising it only on that side. If not a routing issue, any ideas as to what might be going on here? I can provide more information if needed.
Thanks for your time.
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