02-13-2020 06:57 PM
Network infrastructure consists of multiple stores connected with MPLS, everything back hauled to our data center for internet and resources. Every store has a router and a switch on premise, except for one which i will get to in a moment. Every router and switch has a Loopback assigned for us to connect. At one store we have the router and 2 switches, think a main backbone (L3 - 3850)and a downstream (L3-3750). Today the last PC got moved off of VLAN 1 on the downstream switch and immediately we lost remote connection. The switch is up and operational but I have no connectivity. Both switches are running EIGRP. Looking at the configs it appears that the downstream switch had it default gateway and an ip route statement using the IP address on VLAN 1.
Before my time the loopbacks were setup to use a single IP and get advertised in EIGRP. Is there a best practice to setup a connection between 2 L3 switches? We were using the IP address of VLAN 1 to connect to this downstream switch as the assigned loopback never worked.
The router to the backbone uses a point to point which is advertised also in the EIGRP table. Is it best practice to use loopbacks at a "management" access IP? Could i use a point to point to connect both switches?
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02-13-2020 07:20 PM
02-13-2020 07:20 PM
02-13-2020 07:43 PM
It may be best to show you a snippet of the issue - remote connectivity.
Backbone1
router eigrp 50
network 172.18.1.116 0.0.0.3<<<point to point with Router
network 172.18.5.34 0.0.0.0 <<<Loopback address
network 192.110.100.0
eigrp stub connected summary
ip default-gateway 192.110.100.1
interface Vlan1
ip address 192.110.100.1 255.255.255.0
Downstream1
router eigrp 50
network 172.18.5.35 0.0.0.0<<<Loopback address - unable to connect
network 192.110.100.0
eigrp stub connected summary
ip default-gateway 192.110.100.1
interface Vlan1
ip address 192.110.100.1 255.255.255.0
Also when the change was made we created a loopback address for the 198.110.100.x network on our CORE switch within out datacenter for some NATing we preform on our ASA. To circle back I can remotly connect to the store router and the backbone switch but not the downstream switch(using loopback or VLAN IP).
02-13-2020 08:50 PM
02-14-2020 04:42 AM
Yes that was a typo, my apologies!
Downstream1
interface Vlan1
ip address 198.110.22.6 255.255.255.0
I'm a bit confused, if I can access the backbone currently via the loopback 172.18.5.34 then why change it? For the infrastructure as a whole we are using the 172.18.5.0/24 range for the loopbacks for all cisco devices. If I had another IP available in that range 172.18.5.x would assigning it to VLAN1 on the backbone and by using the ip route statement on the downstream and then advertise in EIGFRP correct the issue?
02-14-2020 10:25 AM
Backbone1
router eigrp 50
network 172.18.1.116 0.0.0.3<<<point to point with Router
network 172.18.5.34 0.0.0.0 <<<Loopback address
If I had another IP available in that range 172.18.5.x would assigning it to VLAN1 on the backbone and by using the ip route statement on the downstream and then advertise in EIGFRP correct the issue?
172.18.5.34 is already assigned to loopback interface on the core. If you try to assign another IP in the 72.18.5.x/24 range to vlan1, you will get a duplicate address error. That is the reason, you need a different subnet for vlan1.
HTH
02-15-2020 04:50 PM
02-26-2020 01:59 PM
I created a new VLAN/30 for the switches to communicate. When I removed the default gateway statement off of the downstream i lost remote connectivity again. I added the IP of the backbone as the default gateway and it worked. Thank you for your assistance.
02-26-2020 07:09 PM
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