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Effects of OSPF and trunk?

CourtneyKPrin
Level 1
Level 1

Two distribution switches connected to each other with bundled trunk ports using src-dst-ip load-balance and have an OSPF adjacency. They have SVIs in the same subnets as each other to segment different traffic (voice, servers, wireless, etc).  Some hosts are configured with a gateway that resides on the closets distribution switch and allows limited routing if the physical links between the distribution switches was severed. The IP route table shows more than one route between the switches and uses VLANs as the interfaces.

 

I have been directed to configure 'passive-interface default' and make the exception to one VLAN with 'no passive-interface vlan 3' until there's a migration plan to create new subnets and use just OSPF between the distribution switches.

 

Will the routed OSPF traffic be tagged with VLAN ID 3? If yes, will there be a security risk to servers on VLAN 3?

Will the routed OSFP traffic be load balanced on the ether-channel?

 

 

 

20 Replies 20

Hello Jon

I have stated the same in a previously  edited post.

 

@CourtneyKPrin wrote:

Are you sticking to that the routed traffic is not being tagged?

 

No Communication between users vlan 3 isn’t routed, they are switched over the trunk between site A/B and are tagged( unless otherwise stated), users in vlan3 only need to be routed via their D/G if they need to communicate outside their own vlan but OSPF isn't required for this to happen unless its to a network that site A/B dont share.


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Kind Regards
Paul

 

Post removed as it was unnecessarily argumentative on my part. 

 

Jon

 

Paul 

 

Apologies for the unnecessary post, just having a bad day. 

 

Based on what you said I think your answers are more accurate than mine. 

 

Jon

I apologize for confusing the network design. The routing table I referenced is more accurate than my attempt at using text to show the design. I was showing how OSPF and the trunk were formed between the two switches. Jon is correct and the question is about the subnets that don't have SVIs on both sides and if they are being tagged with VLAN 3, such as subnet 10.0.20.0/24.

 

I got a reply from Cisco TAC yesterday, "The OSPPF adjacencies  is formed over the interface VLAN  and the VLAN traffic is tagged with VLAN 3 on the trunk  interface".

 

To those asking why I don't use a dedicated VLAN or use IP to form the OSPF neighborship, that is my intention but have been told not to.

Hello

Thanks for the clarifications, as that's what is expected based on what you explained and shown with the route table outputs.

 

Communication between users vlan 3 isn’t routed, they are switched over the trunk between site A/B and are tagged( unless otherwise stated), users in vlan3 only need to be routed via their D/G if they need to communicate outside their own vlan but OSPF isn't required for this to happen unless its to a network that site A/B dont share.

 

 

 

 

 


Please rate and mark as an accepted solution if you have found any of the information provided useful.
This then could assist others on these forums to find a valuable answer and broadens the community’s global network.

Kind Regards
Paul

for security why you not config direct OSPF neighbor IP, this make hello message not multicast to all attach PC&Server in VLAN subnet BUT unicast it to only neighbor IP.

for the port-channel I think the traffic since the source and distention is same then the traffic will flow through unique only one link for port-channel and it it failed then it will change to other link. 

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