The most messed up topology.

Hey all,

I'm not going to describe the reasoning here, as it's not mine, but here goes:

I have an Elementary School with an HP 5406zl for a core. A separate site connected via an IDF running on older Cisco gear (Cat 3750/3560). Edge at the Elementary are HP 2920 (which is also how the separate core is connected - and worked before the following scenario). Admin decided to conform to Cisco, so they ordered 3 Cat 9200s for a new IDF during a site upgrade. Once that 9200 came online, the 3750 router went down. These two are not directly connected. This topology is making me nuts, and it's moving in the right direction, but I am hoping to find a bandaid in the meantime.

Rundown

HP 5306zl

vlan 18

name "3750G-12PS" < model

tagged C1-C8,C10-C24,D1-D8,F1-F8 < all those admin ports

ip address 10.18.0.1 255.255.255.0

ip helper-address 10.46.1.53

ip igmp

ip igmp forward C1-C24,D1-D8,F1-F8 < forwarding info

ip ospf 10.18.0.1 area backbone

exit

HP 2920 edge hosting 3750 router

interface A2

dhcp-snooping trust

arp-protect trust

name "Trunk to Cisco 3750G-12PS"

exit

Cisco 3750G-12PS

switchport trunk encapsulation dot1k

switchport mode trunk

ip dhcp snooping trust

ip arp inspection trust

Cisco C9200L-48P-4X

Added vlan 18 and interface 18 with no interface.

Switch is acting as an edge switch