OSPF and VLAN Question

certmistercertmister Member Posts: 40 ■■□□□□□□□□
Hopefully this is a quick question. Routing is not my strong point so bear with me here. I set up OSPF on a 3 Router, 3 Switch Network and the Guide I was using said you should be able to ping the Vlan IP of the Switches. I was under the impression that was what ROAS and L3 Switches were for, not Routing Protocols. I mean I can ping all the interfaces on the Routers but if I try to ping the address assigned to Vlan1 it dies. Am I right to assume that without a Trunk and Subinterfaces setup between the Router and the Switch, i.e. ROAS, that OSPF is not supposed to be able to reach the switches.

Comments

  • pham0329pham0329 Member Posts: 556
    ROAS provides inter-vlan routing, but without routing protocols, every network would have to be directly connected to the router for routing to occur. Consider the following
    • Sw1 is connected to R1, and contains vlan 10 and 20
    • Sw2 is connected to R2, and contains vlan 100 and 200
    • R1 is connected to R2
    Without a routing protocol, how would a client in Vlan 10 reach a client in vlan 100? It couldn't because R1 wouldn't have a route to get to vlan 100 and vice versa.
    I mean I can ping all the interfaces on the Routers but if I try to ping the address assigned to Vlan1 it dies. Am I right to assume that without a Trunk and Subinterfaces setup between the Router and the Switch, i.e. ROAS, that OSPF is not supposed to be able to reach the switches.

    No. As long as vlan interface and the router is on the same subnet, and the switchport connecting the router to the switch is assigned to the correct vlan, there should be connectivity between the two.
  • certmistercertmister Member Posts: 40 ■■□□□□□□□□
    Forgot about the switchport. I have had some success with hardcoding the switchport on the switch to an access port, but one of switches is still not reachable even after changing the switchport. The Routers are in the same subnet and Vlan 1 is the only vlan.
  • advanex1advanex1 CASP, MCSA 2016, MCSA 2012, CCNA, Security+, Network+, Project+, Server+ Member Posts: 364 ■■■■□□□□□□
    certmister wrote: »
    Forgot about the switchport. I have had some success with hardcoding the switchport on the switch to an access port, but one of switches is still not reachable even after changing the switchport. The Routers are in the same subnet and Vlan 1 is the only vlan.

    Well, I'm assuming you have your switches all connected to one router and then the other 2 routers as "out sites". This may sound basic, but are you sure that the router interface and the switches management IP's are all within the same subnet?
    Order of Certifications to come: CISM, C|EH, CISA
    2019 certification tests taken: CISSP (Passed - awaiting endorsement), MCSA: 2016 (Passed), CCNA (Re-certification - Passed)
    Currently Reading: CISM: All-in-One
    New Blog: https://jpinit.com/blog
  • certmistercertmister Member Posts: 40 ■■□□□□□□□□
    I figured out the Problem, it's an IP Addressing problem. I'm using the subnet192 guide for this lab. Each Switch connects to a different Router. Here's a basic idea of the Topology:



    Here is the IP Info:



    I think S2's Vlan 1 IP address is wrong, and should be 172.16.0.126 not 172.16.5.126 and I used the proper address on S2 but I never changed the address on R2 to put it in the same subnet. So problem solved I guess but the Guide really needs to be redone because this is not the first error I've seen.
  • pham0329pham0329 Member Posts: 556
    Good to hear it's working, but looking at the diagram, it says
    • R2's F0/0 ip = 172.16.5.1/25
    • S2's VLAN ip = 172.16.5.126/25

    those are on the same subnet...i'm not sure how changing S2's ip to 172.16.0.126 fixed your problem icon_scratch.gif
  • certmistercertmister Member Posts: 40 ■■□□□□□□□□
    Part of the lab was to calcuate the subnets and their ranges and when I did S2's Vlan subnet, it was 172.16.0.126/25 but R2 was 172.16.5.1/25

    I configured S2's vlan as 172.16.0.126 but forgot to change R2 so it was on the same subnet, I have since put them both on the same subnet, i.e. R2 is now 172.16.0.1

    I guess looking back if I had left them as they were in the Table, it would have worked but technically the subnet range was incorrect.
Sign In or Register to comment.