Routing VLAN over multiple routers

[benny6812]

Hi there,

I'm trying to get a vlan to share over two routers, but im stuck. I've read up on tons of stuff but nothing seems to fit in. I was wondering if someone could help me out.

I've attached both the packet tracer and the topology jpeg. It is VLAN 20 that I am attempting to share, my goal is that PC13 on VLAN 20 (standalone) should be able to request an IP from Router 0 (which is DHCP server) as well as full communication between the other hosts on VLAN 20.

Thanks in advance.

[Gregory Snipes]

From what I see in your diagram, it looks like you are attempting to to use the same subnet off of two different routers without layer 2 connectivity between the two of the. The only way you could do something like that would be if you setup a layer 2 tunnel between the sites.

Here is some info on configuring L2TP.

[paul driver]

Hello

You can try ATOM connection.if your router supports it.

Router 1

ip cef

int x/x ( facing router 2)

mpls ip

mpls ldp router-id lo0

int y/y ( facing lan)

xconnect y.y.y.y 12 encap mpls

Router 2

ip cef

int x/x ( facing router 1)

mpls ip

mpls ldp router-id lo0

int y/y ( facing lan)

xconnect x.x.x.x 12 encap mpls

please note the loopback interfaces on the routers require reachability

.

res

Paul

Please don't forget to rate any posts that have been helpful.

Thanks.

[benny6812]

Can you expand on this please

Thanks

[Bilal Nawaz]

Hello Ben, ATOM stands for Any Transport over MPLS. Its a solution to transport layer 2 over an IP/MPLS backbone. However, its not supported in packet tracer either. It's very limited in that aspect. More commonly used with large service providers.

I have provided a white paper link on AToM below:

http://www.cisco.com/warp/public/cc/so/neso/vpn/unvpnst/atomf_wp.htm#wp34608

Hope this helps.

Please rate useful posts and remember to mark any solved questions as answered. Thank you.

[Bilal Nawaz · Accepted solution]

Hi Ben,

In principle this is not possible between 2 routers. Packet tracer does not support this type of thing between routers - as Gregory mentioned you could use L2TP which is not supported in packet tracer or other enhanced protocols. You cant use the same ip address range i.e. 192.168.3.0 network on both sides without a switch / switches catering to carry the frames across to the other side.

I had a go at your lab - was great fun! I have attached my version in this post.

I had the same vlan at both sides, BUT:

one side had the 192.168.3.0 range - on vlan 20 but inaccessible from the other side, because there is no layer 2 connectivity there.

the other side had 20.20.20.0 range - same again, on vlan 20 but there is nothing to cary the frames across - hence different IP subnet

The things I changed were:

• removed servers (not sure what purpose they were serving - maybe it was for DHCP?)
• changed ospf between R0 and R1 for adjacency on the 1.1.1.0/30 network
• setup new dhcp pools on R0 192.168's and on R1 20.20.20.0's
• vlan 20 exists in both places but with different IP schemes
• everything is able to ping everything else.
• changed config on switches so they are trunking relevant vlans (this wasnt the case with your example)
• some trunk configuration on switches and sub interfaces.

R0 on the left:

ip dhcp excluded-address 192.168.2.1 192.168.2.100

ip dhcp excluded-address 192.168.3.1 192.168.3.100

ip dhcp excluded-address 192.168.4.1 192.168.4.100

!

ip dhcp pool SALES

network 192.168.2.0 255.255.255.0

default-router 192.168.2.1

ip dhcp pool ADMIN

network 192.168.3.0 255.255.255.0

default-router 192.168.3.1

ip dhcp pool PUPILS

network 192.168.4.0 255.255.255.0

default-router 192.168.4.1

!

interface GigabitEthernet0/0

no ip address

!

interface GigabitEthernet0/0.10

encapsulation dot1Q 10

ip address 192.168.2.1 255.255.255.0

!

interface GigabitEthernet0/0.20

encapsulation dot1Q 20

ip address 192.168.3.1 255.255.255.0

!

interface GigabitEthernet0/0.30

encapsulation dot1Q 30

ip address 192.168.4.1 255.255.255.0

!

interface GigabitEthernet1/0

ip address 1.1.1.1 255.255.255.252

!

router ospf 1

log-adjacency-changes

network 1.1.1.1 0.0.0.0 area 0

network 192.168.0.0 0.0.255.255 area 0

R1 on the right hand side:

ip dhcp excluded-address 20.20.20.1 20.20.20.100

!

ip dhcp pool VLAN_20

network 20.20.20.0 255.255.255.0

default-router 20.20.20.1

!

!

interface GigabitEthernet1/0

no ip address

!

interface GigabitEthernet1/0.20

encapsulation dot1Q 20

ip address 20.20.20.1 255.255.255.0

!

interface GigabitEthernet2/0

ip address 1.1.1.2 255.255.255.252

!

router ospf 1

log-adjacency-changes

network 1.1.1.2 0.0.0.0 area 0

network 20.20.20.1 0.0.0.0 area 0

Hope this has some benefit for us

Please rate useful posts and remember to mark any solved questions as answered. Thank you.