03-09-2016 04:31 PM - edited 03-05-2019 03:31 AM
Hi guys,
I've set up my own packet tracer file to gain knowledge on how I can get multiple VLAN's to ping over a network with 2 routers, sharing a Serial WAN link using OSPF.
The 2 VLANs connected to each router can ping each other, they cannot ping over VLAN's on other switches. I have attached an image of the screenshot in packet tracer.
I have set up a trunk between each switch and router and
I just don't understand why the VLANs on the 2 switches don't ping between each other?
03-10-2016 12:51 AM
Hello Simonj123,
OSPF is a routing protocol and should be used to route between different IP subnets.
If your network diagram is correct you have duplicated Vlan-ids 10, 20 on switch1 and switch2 (and this wouldn't be a problem), but you have also duplicated IP subnets associated to the Vlans 10,20.
Both vlan10 and vlan20 are associated with IP subnets 192.168.10.0/24 and 192.168.20.0/24.
You cannot use a routed L3 link like the serial link between R1 and R2 to extend the IP subnets between the two routers.
A router is a broadcast firewall it stops the broadcast of a subnet associated to each connected interface or subinterface.
R2 and switch2 could still use Vlan-ids 10 and 20 as they are locally meaningful, but the associated IP subnets must be different like for example 192.168.30.0/24 and 192.168.40.0/24.
If you perform this change you have a correct IP internetwork and you avoid the issue of duplicated IP subnets.
At this point OSPF would allow communication between subnets
192.168.10.0/24, 192.168.20.0/24 attached to R1-SW1 site1
and
192.168.30.0/24, 192.168.40.0/24 attached to R2-Sw2 site 2
R2 OSPF configuration has to advertise the correct attached IP subnets
192.168.30.0/24 and 192.168.40.0/24.
As a final note, your current configuration could work only if between R1 and R2 would be possible to perform bridging instead of routing or using a more complex feature like L2TPv3.
The point is that you need to understand that routing works only between DIFFERENT IP subnets and cannot be used to extend/connect same IP subnets.
Hope to help
Giuseppe
04-27-2017 04:46 PM
Did you got the lab working....??
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