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R2811 with S3750 won't route via default Route

idyllman80015
Level 1
Level 1

I have a 2811 router with default route 0.0.0.0 0.0.0.0 192.168.1.1 (my ISP Lan-side interface).  I have DHCP server on the router for wired interfaces (e.g. 172.16.11.0 /24 through 172.16.18.0 /24) with 8 VLANs (711 - 718), but none of the 172.16 range interfaces will ping the default gateway.  I can Only ping the default from the Router out of Fast Ethernet 0/0, but not any of the Subinterfaces or from the Switch Virtual Interfaces (e.g. interface vlan 711, 712, etc. which are all in the 172.16.x.x range.  NOTE: I don't have any interfaces connected to VLAN 713 or 714, but I do on other VLANS.  I can only get to the ISP Lan-side interface, and subsequently to the Internet, using Wireless interfaces handed out by the ISP's gateway, not the Wired (Cat5 Ethernet) Interfaces, which get their IP Address Assignment from the R2811 Lab Router.  I have tried to implement NAT/PAT, checked the Routing Tables, but I can't figure it out.  I have attached the running-config from the 3750 Switch and 2811 Router.  Any help is greatly appreciated so let me thank you in advance.  

1 Accepted Solution

Accepted Solutions

Hello
You have ROAS being performed on the rtr also L3 svis on the switch, you do not need both also the L3 switch has a incorrect default-gateway address.

See attached file for possible solution.


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

View solution in original post

7 Replies 7

chrihussey
VIP Alumni
VIP Alumni

You did not include the configs in your post.

However if I understand it correctly, only the 2811 can ping the 192.168.1.1 IP of the ISP router and the 172.16 hosts cannot. Can the 172.16 hosts ping the 192.168.1.x IP of the F0/0 interface of the 2811? If so, then the problem is probably that the ISP router needs a route for the 172.16 networks pointing to the F0/0 interface IP of the 2811 router.

Please add the configs if this doesn’t fix the issue.

Regards

Thank you @chrihussey for noticing my config uploads failed.  I had previously uploaded them but I had to step away, so when I got back to my post, I had to repost everything and forgot to re-upload the configs.  Nothing in the 172.16.x.x can ping the 192.168.1.1 nor 192.168.1.114, which is the Fa0/0 ip address of R2811.  I used to have access to the ip route on the ISP Router in the Advanced section, but that is no longer showing.  I will contact the ISP Technical Help desk to have a return route for 172.16.x.x and post an update after my interaction with them.  Thank you for the wonderful suggestions, @chrihussey

idyllman80015
Level 1
Level 1

I called the ISP and they advised they would be unable to help with my issue as they don't support any routers other than their own gateway.  The also advised that they removed the static route configuration for security purposes.  In other words, they can't help me. 
I wasn't surprised that the support technician didn't even understand the difference between Private IP Addresses and Public IP Addresses.  I think they are only trained on their equipment, not how TCP/IP works, but as I said, that doesn't surprise me much.

Richard Burts
Hall of Fame
Hall of Fame

When I read about an issue when the router can access outside resources but inside devices can not, my first guess is that there is an issue with address translation. In looking at the posted config I do not see anything providing address translation. I believe that this is your issue.

HTH

Rick

Hello
You have ROAS being performed on the rtr also L3 svis on the switch, you do not need both also the L3 switch has a incorrect default-gateway address.

See attached file for possible solution.


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

I agree with Paul that you do not need SVIs configured on the switch. And on some layer 2 switches where ip routing is not enabled (and it appears that ip routing is not enabled on this switch) if multiple SVI are configured only one of them will be up. While it is not needed here I do not think that configuring SVI on the switch causes any problem. I checked the DHCP pools on the router and the default gateway for the hosts in each vlan is the router subinterface address for that vlan. So hosts should not be impacted.

The configured default gateway will not work. I note that it is the same address as the next hop for the default route on the router. So that sort of explains where it came from. But the switch has no way to access 192.168.1.1 and so its default gateway will not work. This might have impact on the switch but will not impact connected hosts.

HTH

Rick

I modified some of the suggestions in the attached .txt file, but these suggestions did the trick. When I first tried, I lost connectivity to the switch.  Then I realized that the management SVI was being deleted, along with the other SVIs that were unnecessary.  So I had to reboot the switch and try again. 
I usually put my configs in a notepad .txt file, then paste it into the device.  I would recommend to anyone to NEVER add "write", "write memory", or "copy running-config startup-config" to a .txt file that you paste into a switch or router for this very reason.  I would also recommend that if you are configuring a device to use the "configure terminal revert timer {minutes} <1 - 120>" but be wary of this - it doesn't always work!  There have been some IOS / Platforms which seem to have a bug in this command! 

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