Static routes for discontiguous overlapping subnets on seperate interfaces

I have a routing situation that to me seem's to be set up correctly. My customer is telling me that he thinks how I've set it up is wrong.

The customer is saying he's unable to reach some of the lab's subnets in the allocated /21 from the LAN. He believes I can't have a single route pointing at the 10.10.20.0 /21 because he has it divided into multiple smaller subnets inside his lab. He believes I need to put a static route for every single subnet he has on the LAN edge router. I don't believe that is the case. The remote sites are using subnets carved out of that /21 as well, but there are more specific routes for those networks, so I don't think that's an issue either.

I've done traceroutes from the edge router and they always go the right way.

I'm not 100% sure what the issue is on his side, he's not really willing to provide me with exact details or configurations. I just want to be sure my end is set up ok.

If my side is right, does anyone have a theory on what he may be doing wrong inside the lab? He is using the 10.10.20.0 /24 as his core subnet. Could that cause any issues in this case? Diagram
EyediedLead Network EngineerAsked:
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kuohConnect With a Mentor Commented:
Logically, there isn't anything wrong with that. In fact, that is the normal way it should be done. But again, there may be something else we're not seeing in the config.

KuoH
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kuohCommented:
Since the LAB RTR LAN IP is 10.10.20.1/24, what are the other /21 lab subnets using as their default gateways?  Are they using /21 or /24 netmasks?  Simply pointing them to 10.10.20.1 wouldn't work if they're not on the same /24 subnet as the router.  It's hard to troubleshoot if the other side isn't willing to cooperate, but if you can show that traces from your LAN to each of the LAB subnets terminates at the LAB RTR, then that should be sufficient to show that your side is routing correctly.

KuoH
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OLY8892Commented:
He needs to create sub interfaces Lab RTR for his other lans to have default gateway
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EyediedLead Network EngineerAuthor Commented:
I think I might have mis-represented his lab device. I believe he's using a 6500. He's using VLAN interfaces for each subnet as the gateways.
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EyediedLead Network EngineerAuthor Commented:
@kuoh

He has /21 divided into multiple subnets of different sizes. I believe, but am not positive that he is using the correct masks and using an IP from that subnet as the gateway which are put on VLAN interfaces on a 6500.
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kuohCommented:
But the problem is that you can't verify that he is doing it correctly on his end.  It seems that the only way you might be able to make him happy, and prove him wrong, is to add the more specific routes like he asks.  Then when it still doesn't work, you can get him to take a closer look at his config.  Without seeing the configs on both sides, it's not easy to pinpoint the source of the issue.

KuoH
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EyediedLead Network EngineerAuthor Commented:
I have a meeting set up with him today. Hopefully we can figure this out. But just so I'm sure, is there anything wrong with how I have the static for the /21 pointing at his router even though there are /24 from that /21 at the remote sites?
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EyediedLead Network EngineerAuthor Commented:
So after talking with the customer more it turns out his initial explanation of what was happening was way off. Turns out only the 10.10.20.0 /24 was accessible. As soon as he told me that I knew there was an incorrect mask somewhere. So I got on the firewall and found the static route for the 10.10.20.0 /21 was set as a /24. This ironically was changed a few weeks ago when we were troubleshooting during the initial build of this lab and couldn't get the routing to work. Apparently the mask never got changed back.

This exercise wasn't lost however. At least we confirmed the config on the router was correct after all.

Thanks for the help guys!
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