VLAN interfaces and routing

[CameronS]

We are running into issues with our VLAN configuration when making some changes. For reference:

initial config:

• L3 MS225 core switch stack
  
  • client VLAN 1
    • Interface IP set (subnet gateway x.x.x.252)
    • Do not respond to DHCP
• MX105 HA
  • static route route for VLAN 1
    • Route all to management interface of core switch stack
  • Do not respond to DHCP
• 2 DHCP (HA) servers both using VLAN 1 addresses

This works without issue but very messy IMO

New config (replicating other client VLANs):

• Core switch stack
  • client VLAN 1
    • interface IP set (x.x.x.1)
    • Do not respond to DHCP
• MX105 HA
  • Remove static route
  • Add client VLAN 1
    • MX IP set to the gateway address x.x.x.252
    • Do not respond to DHCP
• No change to DHCP servers

The changes are to change which L3 device becomes the gateway and allow for seamless routing within VLAN 1.

For some reason the above changes just breaks the VLAN. All other client VLANs are setup this way but are relaying DHCP to the DHCP servers that sit in VLAN 1 (I know we should probably have interfaces for the other client VLANs too). The issue must lie with DHCP in my head but I cannot figure out what exactly so hoping some of you geniuses could help.

TIA

[alemabrahao]

What do you mean by breaks the VLAN? Can you explain the problem better?

[alemabrahao]

Another thing, in the DHCP configuration who is the network gateway? If it's the Core siwtch, you need to have a default route pointing to the MX IP.

[CameronS]

Apologies. After the changes, no devices can communicate on VLAN 1 including the DHCP server which in turn causes issues with our other VLANs client addressing (due to bad DHCP settings). The scope uses .252 as the gateway which was the core switch but then changed to the MX.

[alemabrahao]

First question, can you reach the gateway?

[CameronS]

I couldn't test this at the time as the VPN connection went down (authenticates via AD which happens to be on VLAN 1).

[DarrenOC]

Hi @CameronS , doesn’t look like this progressed very far.  You still stuck? What are your next steps?

[PhilipDAth]

>The changes are to change which L3 device becomes the gateway and allow for seamless routing within VLAN 1.

What is happening here is the MAC address of the default gateway is changing, and clients have not picked up the change.  If you give the switch a reboot after doing this (so all the ports go down and up) the clients will refresh their arp caches.

[CameronS]

This makes more sense, I'll try this out.