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VLAN / Routing Question

Occasional Contributor

VLAN / Routing Question

Hi all -

Feeling a little silly here as this has me scratching my head. I have just sent over a pair of new 2920 switches to a new facility we are standing up. We have verified with our ISP that the MPLS at this new site is up and running. In fact, I can access each of the 2920's in the new facility from our corporate HQ no problem... so the basics are certainly in place.

So, I can ping the switch's default VLAN IP address ( no problem (VLAN ID 1). I can ping the IP address of what will be a WiFi VLAN as well (, which is VLAN ID 2). I can ping each of these from my corporate HQ network, over the MPLS, so I think my setup and routing is OK. BUT, if I plug in a device into VLAN ID 2 on the remote switch, I get nothing. The endpoint device will not get DHCP, and even if I statically configure IP on the endpoint device, I cannot access it. not even from the default VLAN on the same switch...? This is my config. I can't show the config of the default (MPLS) router as it is managed by the ISP... Not sure what I am missing?? THANKS!!

Running configuration:

; J9727A Configuration Editor; Created on release #WB.15.12.0015
; Ver #05:18.41.ff.35.0d:9b

hostname "net-florida-05"
module 1 type j9727a
dhcp-snooping vlan 2
time timezone -5
ip default-gateway
ip route
ip route
ip route
ip routing
interface 23
   speed-duplex 1000-full
snmp-server community "nacoi" operator unrestricted
snmp-server contact "David Levine" location "Flaggler"
   no ip address
vlan 1
   name "DEFAULT_VLAN"
   no untagged 19-20
   untagged 1-18,21-24,A1-A2,B1-B2
   ip address
   ip helper-address
   ip helper-address
vlan 2
   name "WiFiVLAN"
   untagged 19-20
   tagged 23-24
   ip address
   ip helper-address
   ip helper-address
no tftp server
no autorun
no dhcp config-file-update
no dhcp image-file-update
password manager
password operator

Honored Contributor

Re: VLAN / Routing Question

uess you need to break that down into two seperate issues to troubleshoot.

First issue:
When you configure a host with an address in the subnet, then patch it to the 2920 on a switchport between 1-18 or 21-24
- can it ping its default GW?
- can it ping
- can it ping

Second issue:
After attempting to use DHCP on the remote site on a switchport between 1-18 or 21-24, does your scope on your DHCP server show that any lease has been reserved for an offer?

More generally, you have a serious design issue: you have hosts on the same subnet as a Layer-3 link. You should never do this.
Your hosts will use 54.5 as their default GW (presumably) which will then route the packets to 54.1. Return traffic will arrive at 54.1 which will see the destination address as a local subnet and attempt to switch it directly to the host.
This gives you asymmetric routing.
Also, you are assuming the device with 54.1 has a mac-address-table big enough for all your VLAN1 hosts PLUS the switch. Very bad design.
Your link to 54.1 should be on a dedicated VLAN/subnet with no other devices.

Occasional Contributor

Re: VLAN / Routing Question

Thanks for the reply Vince.

So, I understand what you are saying about design. I guess I didn't think about the MAC address table on the gateway router. This is for a pretty small network - I don't expect us to grow beyond 15 hosts in total.

I can plug hosts into the switch (VLAN 1) and access everything required. The laptop, desktop, etc. will obtain a DHCP address from the remote DHCP server. It will be given an IP address such as with a default gateway of Everything works fine. Pings to, are OK. Internet Is good as is access to our corporate HQ on the other side of the MPLS.

Where I have the issue when I put a host on VLAN 2 on the switch ( I would expect the host plugged into this VLAN to get a DHCP address such as with a default gateway of This is not happening though. I did test this on our bench before the switch was shipped.

Talking to the ISP / MPLS provider now. Maybe we had a miscommunication there...?



Occasional Contributor

Re: VLAN / Routing Question

Update - for some reason the ISP put a sub-interface / IP address on thier router that was They also had a route that said the next hop for the network was (our 2920 switch). 

This was a problem.

As soon as they removed from thier router, everything started working.

Yeesh :)