Inter-vlan routing not working on the C3750X Layer 3 Switch. Help!!!

[elom.kutsienyo]

Hi all,

Just configured a 3750x switch as a DHCP server for some vlans and even though the ip routing is enabled, I am unable to route between vlans.

Note that the 3750x serves as a core switch that connects through trunking to 2960s accesss switches. VTP v3 is enabled, as well as VTP pruning, all SVIs configured. DHCP gives the respective SVI as gateway for the PCs. The computers connect through IP phones so the ports on the 2960S are on multi-vlan access mode.

I am wondering why I am unable to route between my vlans as I can see all subnets on respective SVIs in the routing table of the switch. I also used the default gateway comand on the 2960S switches so they are able to ping all the SVIs but the PCs on the access ports are not able to do the same and possibly exchange information with each other on different networks.

Thanks in advance for your help.

Regards,

Igor

[Partha Dasgupta]

Hi,

Can we try removing the command

system mtu routing 1500

and verify

Regards

Partha

[elom.kutsienyo]

Thanks for your reply but:

This command from what I checked is not concerned by SVI interfaces and also affect only 10/100 interfaces and I am using gigabit interfaces. It was configured  int the device by default and I read that 3750x switches find it difficult to route packet that exceed the MTU.

https://supportforums.cisco.com/thread/2067727

Please can someone confirm that removing the command

system mtu routing 1500

can solve my issue???

Thanks.

[Reuben Farrelly]

Can you post the output of 'show ver' and 'show sdm prefer' ?  It sounds almost like you have a 3750X with the LANBASE featureset (which IIRC doesn't support IP routing).

[elom.kutsienyo]

Hi Reuben

Please here are the show commands you requuested.

[Karsten Iwen]

So it's IPServices with the default-template. That really should work with your routing-needs.

Can you please answer the following question with "debug ip icmp" enabled on the switch?

There is also no output if you ping 192.168.10.254 from the PC?

-- 
Don't stop after you've improved your network! Improve the world by lending money to the working poor:
http://www.kiva.org/invitedby/karsteni

[elom.kutsienyo]

Update on the issue:

I connected a router to a port of the 3750x, and from the pc on the access switches, am able to ping the SVI of the vlan for the router but am not able to ping the router itself. Even though the core switch itself is able to ping the router.

[Raja_D]

Elom, 

Do you just have one 3750 and one 2960 router or one 3750 connecting to several 2960 routers ? If its of one single 3750 router then is that 3750 connected through one physical link connection to 2960 router ? please share the Network topology for better understanding

[glen.grant]

    So  the pc's are pulling an address in the correct subnet with the correct gateway ?  Little unclear from previous posts.  Also any host ports should have portfast turned on .  Do a show vlan and make sure all vlans are active and the ports show assigned into the correct ports.  Do a ipconfig on the pc's and make sure addresses on devices look correct .  Any pc devices you are trying to ping make sure all windows firewalls are "off" .  Besides that , the config looks ok and see no reason it shouldn't work unless it's an issue with the phones themselves . 

[elom.kutsienyo]

Thanks for your response.

The PCs are receiving proper configurationm I doubled checked, and firewall too are disabled as I am able to ping the PCs from the 3750x switch. There is no phone currently installed on the ports at the access switch level. The PCs are directly plugged in. Also portfast was enabled by default on my switches so am good there too. All SVIs are showing UP UP when I do a "show ip interface brief".

Me too I am wondering why it is still not working.

I need a CCIE here.

[Reuben Farrelly]

Also have you created the VLANs in the switch itself?  I'm not referring to the Layer 3 interfaces but the actual VLANS in the vlan database.  These are missing from your switch config (I guess it's possible your switch has populated the vlan database via VTP though).

Please post "show vlan" output as this will confirm this.

We should be able to solve this without a CCIE, this is CCNA level stuff ;-)

[elom.kutsienyo]

@Reuben I did a show vlan and am able to see the vlans created on the core switch and even the ports that are assigned to them. I was suprised to see that they do not show in the running config.

I am guessing... could it be the fact that I am using vtp v3, as i had to go to enable mode and do "vtp primary vlan" command before I was able to create the vlans.

I have passed two of the CCNP exams myself already and I don't remember anything in my reading that tells me of such a problem... even in the TSOOT book that I am currently reading.

This issue is making me feel as if am not a good network engineer.

[shillings · Accepted solution]

Have you run the debug ip icmp command on the 3750-X, as per Karsten's suggestion yesterday? Depending upon the situation, it might be best to ensure that you only send output to your log, not the command line interface. Setup the debug and then jump onto one of the clients and run a ping to an SVI on the 3750-X. If the 3750-X receives the ICMP requests, then you'll see them in the log (one for each echo request.)

Testing the other way can be done by running wireshark on a client. Then jump onto the 3750-X and source a Ping from another network (either the VLAN ID or SVI IP address): -

ping x.x.x.x source vlan xx

ping x.x.x.x source x.x.x.x

I would also connect a client machine directly to the switch, in case the problem is related to the IP phones. Amend the switchport config accordingly.

[elom.kutsienyo]

Just solved the issue. Steps followed:

- do a no ip routing
- save the config
- backup config to flash
- erase startup config
- reload the 3750x switch
- copy config from flash to run
- enter command ip routing

And here I was with everything running smoothly. Thanks all for all your help. Apparently there was a glitch somewhere. Gotta go finish the ACLs and NAT.

Regards,
IGOR.

Sent from Cisco Technical Support iPad App

[chrisbahuka]

hi 

sorry my english is not very good

i have the same problem with my C3850  , so if we put static route between vlans it will work ??

and if you can assist me with some ACLs and NAT configuration

Thanks you 

Christopher 

[Titus CS]

share output for below command

sh ver