VLANs, DHCP, and Layer 3 routing

[nater]

Ultimate desired network layout:

• 10 VLANs, with one private subnet per VLAN
• Layer 3 routing on core switches
• DHCP servers for most of those VLANs (ideally running on the switches)
• ExtremeCloud IQ Site Engine for WiFi authentication

Where things are at now:

• Network running in a largely out-of-box state (7520-48Y-8C core switches, 4120-48MW-4Y switches in IDFs, AP5010 APs up and running with a single SSID), single VLAN, all switch ports set to access.

I started to things up by updating our switching network policy in ExtremeCloud IQ with the VLANs, and then connected to the command line on one of our 7520 switches and did a "configure vlan ..." with a virtual address IP for each subnet in each VLAN. However, when I went to the switch in the dashboard and checked Monitoring > Routing the status of those VLANs was "DOWN", not "UP". I wanted to try to diagnose things on the 7520 however I ran into some odd issues just getting a DHCP IP address on my laptop via the SFP+ RJ-45 transceiver I was using (I could get link, but not DHCP, and manually setting the IP address didn't work either). So I did an "unconfigure vlan ..." on our 7520 for now... am I missing a step?

I also haven't found any concrete examples of using multiple DHCP servers on Extreme switches to service requests from multiple VLANs. Is this a tested and supported configuration?

I'm very familiar with VLANs and Layer 3 routing with multiple DHCP servers on Cisco and Meraki switches with a Windows DHCP server (using "iphelper", I've read that "bootprelay" is the Extreme switch equivalent), however my current environment does not have a Windows DHCP server and up until now relied on one built into a Ubiquiti firewall. I could set up multiple DHCP servers per VLAN on our new Palo Alto firewall but I think that would involve moving layer 3 routing to the firewall, and I'd rather have that duty fulfilled by the 7520 core switches.

Also, what is the recommended process for changing inter-switch links to trunks from access and have them maintain cloud access? I'm used to Meraki and Cisco switches letting me explicitly specify the VLAN and IP of the switch so that it can communicate over trunks on a particular VLAN and IP. How does an Extreme switch cope in terms of talking to the cloud if it was getting it's IP address via an upstream access port connection and now it has a trunk connection upstream, and what's the best way to change over an out-of-box Extreme network to one with trunks, VLANs, and multiple subnets?

[Brent_Addis]

Hi Nater,

Yes it's supported, we do it ourselves. Are you running VOSS or XOS?

I suspect you are running XOS so I'll base it on this OS.

You likely know this, but in order for a vlan to be in an up state, it needs to be tagged to an enabled interface.

If you are coming from the Cisco world it may be a little different in the way vlans are tagged/untagged. There is no concept of a trunk like in Cisco land.

EG:

If you want the PVID to be vlan2 -> configure vlan 2 add ports 10 untagged

If you want a tagged vlan -> configure vlan 10 add ports 10 tagged

An example setup might be:

create vlan MyVLAN tag 10
configure vlan MyVLAN ipaddress 192.168.0.254/24

configure vlan MyVLAN dhcp-address-range 192.168.0.1 - 192.168.0.200

configure vlan MyVLAN dhcp-lease-timer 86400

configure vlan MyVLAN dhcp-options default-gateway 192.168.0.254

configure vlan MyVLAN dhcp-options dns-server primary 1.1.1.1

configure vlan MyVLAN dhcp-options code 66 string "TFTP server address"

enable ipforwarding vlan MyVLAN

configure vlan MyVLAN add port 1 tagged

configure vlan MyVLAN add port 2 untagged

save configuration

Optional: Troubleshooting

Check your forwarding db and check your mac is showing on the right vlan:

show fdb

Clear DHCP Address Allocations:

clear vlan MyVLAN dhcp-address-allocation all

Remove DHCP Configuration:

unconfigure vlan MyVLAN dhcp

Remove Specific DHCP Options:

unconfigure vlan MyVLAN dhcp-options dns-server primary