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No DHCP crossing over trunk

ChristopheVL
Level 1
Level 1

Hi,

Problem:

No DHCP offers over a wireless trunk for a newly created Vlan (vlan 160 in this example). 

Infrastructure:

Access Switch: WS-C2960+24PC-S
Distribution Switch:  WS-C2960S-24TD-L 

Situation:

I have created a DHCP and a SVI on the distribution switch for vlan 160 + tagged this vlan over the trunk on both switches.
When i assign a port on the Access Switch for vlan 160 i receive Apipa address, but when i assign a port for vlan 160 on the distribution switch everything is working well.

When i revert the changes and only create a DHCP on the access switch it is also receiving apipa address!

If i assign my laptop an ip address in subnet vlan 160 i can't ping the gateway. When i iniate a ping from the access switch to distribution switch i can ping the gateway.

Config on Distribution switch:

DHCP config

ip dhcp pool VLAN160
network 10.3.10.0 255.255.255.0
default-router 10.3.10.1
dns-server 8.8.8.8 8.8.4.4
lease 3

VLAN config

vlan 160
name MGMT-WL

TRUNK config

interface GigabitEthernet1/0/24

description UPLINK WIRELESS BRIDGE
switchport trunk allowed vlan 10,100,160,200,345,450,455
switchport mode trunk
speed 1000
duplex full

SVI

interface Vlan160
ip address 10.3.10.1 255.255.255.0

Config on Access switch:

Trunk config

interface GigabitEthernet0/1
description uplink Wireless Bridge
switchport trunk allowed vlan 10,100,160,200,345,450,455
switchport mode trunk
media-type rj45
speed 1000
duplex full

VLAN config

vlan 160
name MGMT-WL

Port config

switchport mode access
switchport access vlan 160

Any help is welcome,

Christophe 

12 Replies 12

Mark Malone
VIP Alumni
VIP Alumni

Hi

have you checked stp

show spanning-tree vlan 160 on each switch when you cant ping or get dhcp

can you post the show int trunk as well from each switch

Hi Mark,

Thx for your quick reply!

Yes i have and noticed that i have 2 root bridges for this vlan.

One more thing to add, we have a DHCP (Windows server 2008 for data and voip that works well).

Its only with this newly created vlan

Access Switch

Port Mode Encapsulation Status Native vlan
Gi0/1 on 802.1q trunking 1
Gi0/2 on 802.1q trunking 1

Port Vlans allowed on trunk
Gi0/1 10,100,160,200,345,450,455
Gi0/2 450,455

Port Vlans allowed and active in management domain
Gi0/1 10,100,160,200,345,450,455
Gi0/2 450,455

Port Vlans in spanning tree forwarding state and not pruned
Gi0/1 10,100,160,200,345,450,455
Gi0/2 450,455


VLAN0160
Spanning tree enabled protocol rstp
Root ID Priority 32928
Address 6899.cddc.2300
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32928 (priority 32768 sys-id-ext 160)
Address 6899.cddc.2300
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec

Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi0/1 Desg FWD 4 128.25 P2p

Distribution Switch

Port Mode Encapsulation Status Native vlan
Gi1/0/1 on 802.1q trunking 1
Gi1/0/2 on 802.1q trunking 1
Gi1/0/24 on 802.1q trunking 1

Port Vlans allowed on trunk
Gi1/0/1 1-4094
Gi1/0/2 1-4094
Gi1/0/24 10,100,160,200,345,450,455

Port Vlans allowed and active in management domain
Gi1/0/1 1,10,100-103,160,200-201,255,300,345,450,455,500
Gi1/0/2 1,10,100-103,160,200-201,255,300,345,450,455,500
Gi1/0/24 10,100,160,200,345,450,455

Port Vlans in spanning tree forwarding state and not pruned
Gi1/0/1 101-103,160,200-201,255,300,345,450,455,500
Gi1/0/2 1,10,100-103,160,201,255,345,450,455,500
Gi1/0/24 10,100,160,200,345,450,455

VLAN0160
Spanning tree enabled protocol rstp
Root ID Priority 32928
Address 1c1d.86d2.9200
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32928 (priority 32768 sys-id-ext 160)
Address 1c1d.86d2.9200
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec

Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi1/0/1 Desg FWD 4 128.1 P2p
Gi1/0/2 Desg FWD 4 128.2 P2p
Gi1/0/24 Desg FWD 4 128.24 P2p

Hi

where is your root supposed to be for this vlan , is the dist switch acting as the stp root for all vlans or is there a core switch doing that.

Did you use vtp to transfer the vlan or is it manually configured on each switch, something's obviously off there should not have 2 roots same vlan

Do you have specific stp settings configured on each switch

Hi,

I have configured both switches in transparent mode.

The distribution switch should function as the root for all vlan's.

Access switch

spanning-tree mode rapid-pvst
spanning-tree extend system-id
spanning-tree vlan 1,10,100 priority 24576

Distribution switch


spanning-tree mode rapid-pvst
spanning-tree extend system-id

I have noticed that is not correct configured, because this could indicate why their are 2 switches battling to be root , correct?

Should i remove from access?

spanning-tree extend system-id
spanning-tree vlan 1,10,100 priority 24576

Thanks,

Christophe

Hi

yes first thing is to correct stp , set the dist switch as the primary for all vlans if that's what its supposed to be

spanning-tree vlan 1,10,100............. priority 4096

Then check again what stp shows , this change will cause a re-calculation at layer 2 for a second nd longer depending on the stp domain , incase you have anything critical connected to the switches you might want to plan it.Its very quick but can have a slight knock on effect

Ok thx for your support!

I'll plan this in the evening.

I'll come back to you with this

Yes let us know how it goes if its not the fix we can look at other things but best to fix the obvious issue first

Good evening Mark,

I've made the distribution switch root for vlan 160 with priority 4096 = 4256, but when spanning-tree recalculates the access switch stays root bridge, so is the distribution switch. 

I'm not able to remove the spanning-tree system extended-id. 
I receive an error "This platform requires that the extended system-id feature remain enabled"

I've thought about changing the priority number, but don't think this will change something.

Access switch = 128.25
Distribution switch = 128.24

Can the reason be the wireless bridge speed, because it's variable on both sides?

I also tried on the distribution switch with command

spanning-tree vlan 160 root primary, but this one doesn't seem to be accepted.

Thanks

Hi

sorry slow reply I was off few days , just quick thing if you bypass the wireless unit do you get the same result  , as its looks like the  wireless unit may not be passing stp causing the issues, a quick test would be connect the switches direct to each other ?

The only other thing I can think is something is not taking in the layer2 database correctly and the vlan should be  manually reapplied but I think the wireless sounds a bit suspect blocking bpdu traffic

Good morning Mark,

Np!

That's abit difficult because this is production.
I have allready deleted and recreated the vlan multiple times and reloaded both switches.

We have allready had multiple problems with the wirelss bridge and the last change we did was the vendor putting a small netgear switch between it.

Which now explains why it is not working:

I just realise it's also a trunk where we need to add the vlan to it.

Let me try to add it and test it.

Apoligies for "wasting" your time.

Christophe

no probs , sure if you have deleted and re-created theres no point in that again , let me know if adding it to the netgear resolves it

Hi Mark,

I also noticed i don't receive any BPDU packet from the distribution switch to the access switch 

but it does transmit from the distribution switch

401703: .May 27 15:42:17.621: RSTP(450): sending BPDU out Gi1/0/24
401704: .May 27 15:42:17.621: RSTP(455): sending BPDU out Gi1/0/24
401705: .May 27 15:42:17.621: RSTP(200): sending BPDU out Gi1/0/24
401706: .May 27 15:42:18.617: RSTP(160): sending BPDU out Gi1/0/24
401707: .May 27 15:42:18.622: RSTP(100): sending BPDU out Gi1/0/24
401708: .May 27 15:42:19.624: RSTP(345): sending BPDU out Gi1/0/24
401709: .May 27 15:42:19.624: RSTP(10): sending BPDU out Gi1/0/24
401710: .May 27 15:42:19.624: RSTP(450): sending BPDU out Gi1/0/24
401711: .May 27 15:42:19.624: RSTP(455): sending BPDU out Gi1/0/24
401712: .May 27 15:42:19.624: RSTP(200): sending BPDU out Gi1/0/24
401713: .May 27 15:42:20.625: RSTP(160): sending BPDU out Gi1/0/24
401714: .May 27 15:42:20.625: RSTP(100): sending BPDU out Gi1/0/24
401715: .May 27 15:42:21.632: RSTP(345): sending BPDU out Gi1/0/24

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