Ping from vlan interfaces on 3750 switch

Daniel McLean · ‎05-28-2013

Hi all,

I'm having some trouble getting my head round the following but I think it's routing related?

I have a Cisco 3750 switch with the following configured:

------------------------------------------------------------

interface Vlan1

ip address 192.168.0.223 255.255.254.0

no ip route-cache

!

interface Vlan6

ip address 10.74.6.1 255.255.255.0

no ip route-cache

!

interface Vlan8

ip address 10.74.8.1 255.255.255.0

no ip route-cache

!

interface Vlan10

ip address 10.74.10.1 255.255.254.0

no ip route-cache

!

interface Vlan14

ip address 10.74.14.1 255.255.255.0

no ip route-cache

!

ip default-gateway 192.168.0.254

---------------------------------------------------

The 3750 is connected to a firewall which handles the routing. From the 3750 I can only ping remote networks from the vlan1 interface not from vlan6,8 or 10 i.e ping 10.34.37.101 (remote network) source 192.168.0.223 (vlan1) works but ping 10.34.37.101 source 10.74.10.1 (vlan10) does not? I can ping 10.34.37.101 from computers on the various vlans but not from the 3750 it self.

I looked at setting a default gateway for the various vlan interfaces but couldn't find any information so I guess my logic for that is wrong?

Any suggestions?

Thanks

Richard Burts · ‎05-28-2013

Daniel

We need some additional information before we would be able to give you good suggestions about this issue.

- You have configured multiple vlan interfaces on the 3750 which implies that ip routing is enabled on the 3750. Can you verify whether ip routing is enabled on the 3750?

- would you post the output of show ip route from the 3750?

- would you post the output of show ip interface brief from the 3750?

HTH

Rick

HTH

Rick

Daniel McLean · ‎05-28-2013

Hi Richard,

ip routing is not enabled but I have been switching it on to try and get this working. When it's not enabled I think the

ip default-gateway 192.168.0.254 comes into play and when it is enabled show ip route shows the following:

Gateway of last resort is not set

10.0.0.0/8 is variably subnetted, 4 subnets, 2 masks

C 10.74.6.0/24 is directly connected, Vlan6

C 10.74.8.0/24 is directly connected, Vlan8

C 10.74.10.0/23 is directly connected, Vlan10

C 10.74.14.0/24 is directly connected, Vlan14

C 192.168.0.0/23 is directly connected, Vlan1

Show ip int bri:

Interface IP-Address OK? Method Status Protocol

Vlan1 192.168.0.223 YES NVRAM up up

Vlan6 10.74.6.1 YES manual up up

Vlan8 10.74.8.1 YES manual up up

Vlan10 10.74.10.1 YES manual up up

Vlan14 10.74.14.1 YES manual up up

FastEthernet0 unassigned YES NVRAM down down

GigabitEthernet1/0/1 unassigned YES unset up up

GigabitEthernet1/0/2 unassigned YES unset up up

GigabitEthernet1/0/3 unassigned YES unset up up

GigabitEthernet1/0/4 unassigned YES unset up up

GigabitEthernet1/0/5 unassigned YES unset up up

GigabitEthernet1/0/6 unassigned YES unset up up

GigabitEthernet1/0/7 unassigned YES unset up up

GigabitEthernet1/0/8 unassigned YES unset up up

GigabitEthernet1/0/9 unassigned YES unset up up

GigabitEthernet1/0/10 unassigned YES unset up up

GigabitEthernet1/0/11 unassigned YES unset up up

GigabitEthernet1/0/12 unassigned YES unset up up

GigabitEthernet1/0/13 unassigned YES unset up up

GigabitEthernet1/0/14 unassigned YES unset up up

GigabitEthernet1/0/15 unassigned YES unset up up

GigabitEthernet1/0/16 unassigned YES unset up up

GigabitEthernet1/0/17 unassigned YES unset down down

GigabitEthernet1/0/18 unassigned YES unset down down

GigabitEthernet1/0/19 unassigned YES unset down down

GigabitEthernet1/0/20 unassigned YES unset down down

GigabitEthernet1/0/21 unassigned YES unset down down

GigabitEthernet1/0/22 unassigned YES unset down down

GigabitEthernet1/0/23 unassigned YES unset down down

GigabitEthernet1/0/24 unassigned YES unset down down

GigabitEthernet1/0/25 unassigned YES unset down down

GigabitEthernet1/0/26 unassigned YES unset down down

GigabitEthernet1/0/27 unassigned YES unset down down

GigabitEthernet1/0/28 unassigned YES unset down down

GigabitEthernet1/0/29 unassigned YES unset down down

GigabitEthernet1/0/30 unassigned YES unset down down

GigabitEthernet1/0/31 unassigned YES unset down down

GigabitEthernet1/0/32 unassigned YES unset down down

GigabitEthernet1/0/33 unassigned YES unset down down

GigabitEthernet1/0/34 unassigned YES unset down down

GigabitEthernet1/0/35 unassigned YES unset down down

GigabitEthernet1/0/36 unassigned YES unset down down

GigabitEthernet1/0/37 unassigned YES unset down down

GigabitEthernet1/0/38 unassigned YES unset down down

GigabitEthernet1/0/39 unassigned YES unset down down

GigabitEthernet1/0/40 unassigned YES unset down down

GigabitEthernet1/0/41 unassigned YES unset down down

GigabitEthernet1/0/42 unassigned YES unset down down

GigabitEthernet1/0/43 unassigned YES unset down down

GigabitEthernet1/0/44 unassigned YES unset down down

GigabitEthernet1/0/45 unassigned YES unset down down

GigabitEthernet1/0/46 unassigned YES unset down down

GigabitEthernet1/0/47 unassigned YES unset down down

GigabitEthernet1/0/48 unassigned YES unset up up

GigabitEthernet1/1/1 unassigned YES unset down down

GigabitEthernet1/1/2 unassigned YES unset down down

GigabitEthernet1/1/3 unassigned YES unset down down

GigabitEthernet1/1/4 unassigned YES unset down down

Te1/1/1 unassigned YES unset down down

Te1/1/2 unassigned YES unset down down

GigabitEthernet2/0/1 unassigned YES unset up up

GigabitEthernet2/0/2 unassigned YES unset up up

GigabitEthernet2/0/3 unassigned YES unset up up

GigabitEthernet2/0/4 unassigned YES unset up up

GigabitEthernet2/0/5 unassigned YES unset up up

GigabitEthernet2/0/6 unassigned YES unset up up

GigabitEthernet2/0/7 unassigned YES unset up up

GigabitEthernet2/0/8 unassigned YES unset up up

GigabitEthernet2/0/9 unassigned YES unset up up

GigabitEthernet2/0/10 unassigned YES unset up up

GigabitEthernet2/0/11 unassigned YES unset down down

GigabitEthernet2/0/12 unassigned YES unset down down

GigabitEthernet2/0/13 unassigned YES unset down down

GigabitEthernet2/0/14 unassigned YES unset down down

GigabitEthernet2/0/15 unassigned YES unset down down

GigabitEthernet2/0/16 unassigned YES unset down down

GigabitEthernet2/0/17 unassigned YES unset down down

GigabitEthernet2/0/18 unassigned YES unset down down

GigabitEthernet2/0/19 unassigned YES unset down down

GigabitEthernet2/0/20 unassigned YES unset down down

GigabitEthernet2/0/21 unassigned YES unset down down

GigabitEthernet2/0/22 unassigned YES unset down down

GigabitEthernet2/0/23 unassigned YES unset down down

GigabitEthernet2/0/24 unassigned YES unset down down

GigabitEthernet2/0/25 unassigned YES unset up up

GigabitEthernet2/0/26 unassigned YES unset up up

GigabitEthernet2/0/27 unassigned YES unset up up

GigabitEthernet2/0/28 unassigned YES unset down down

GigabitEthernet2/0/29 unassigned YES unset down down

GigabitEthernet2/0/30 unassigned YES unset down down

GigabitEthernet2/0/31 unassigned YES unset down down

GigabitEthernet2/0/32 unassigned YES unset down down

GigabitEthernet2/0/33 unassigned YES unset down down

GigabitEthernet2/0/34 unassigned YES unset down down

GigabitEthernet2/0/35 unassigned YES unset down down

GigabitEthernet2/0/36 unassigned YES unset down down

GigabitEthernet2/0/37 unassigned YES unset down down

GigabitEthernet2/0/38 unassigned YES unset down down

GigabitEthernet2/0/39 unassigned YES unset down down

GigabitEthernet2/0/40 unassigned YES unset down down

GigabitEthernet2/0/41 unassigned YES unset down down

GigabitEthernet2/0/42 unassigned YES unset down down

GigabitEthernet2/0/43 unassigned YES unset down down

GigabitEthernet2/0/44 unassigned YES unset down down

GigabitEthernet2/0/45 unassigned YES unset down down

GigabitEthernet2/0/46 unassigned YES unset down down

GigabitEthernet2/0/47 unassigned YES unset down down

GigabitEthernet2/0/48 unassigned YES unset down down

GigabitEthernet2/1/1 unassigned YES unset down down

GigabitEthernet2/1/2 unassigned YES unset down down

GigabitEthernet2/1/3 unassigned YES unset down down

GigabitEthernet2/1/4 unassigned YES unset down down

Te2/1/1 unassigned YES unset down down

Te2/1/2 unassigned YES unset down down

Port-channel1 unassigned YES unset up up

Once ip routing is enabled I can't ping anything other than connected networks until I set a default route, i.e ip route 0.0.0.0 0.0.0.0 10.74.11.254

but my main problem is from a remote network I can only ping the vlan interface that has the default gateway set, so for example ip route 0.0.0.0 0.0.0.0 192.168.0.254 allows me to ping vlan1 remotely if I change this default route to 10.74.8.254 (the gw for vlan8) then vlan8 interface is now the only vlan interface on the Cisco 3750 I can ping remotely?

Richard Burts · ‎05-28-2013

Daniel

If the intent is that the 3750 should not have IP routing enabled then lets turn it off and then figure out what the underlying issue is and how to fix it.

If IP routing is not to be enabled then the 3750 should have only one layer 3 vlan interface configured (and that should be VLAN 1). Multiple vlan interfaces make sense when IP routing is enabled and it allows the 3750 to route between VLANs. But with IP routing not enabled I would suggest that you remove all but one of the interface vlan x.

Having a single interface vlan x will allow management access to the switch and will allow the switch supervisor to access other network resources. It will not have any impact on layer 2 forwarding or on layer 3 forwarding. And you are correct that in this case the ip default-gateway is configured and used to allow the switch to access IP addresses that are not in the same subnet as its management interface.

I suspect that when you have made the change so that the 3750 has only the VLAN 1 layer 3 interface that layer 2 and layer 3 forwarding will work and that the switch should be able to access the necessary network resources. If that is not the case then we need to check on a few other things. But it looks to me like the issues that you describe are the result of attempting multiple layer 3 interfaces on a switch that is operating at layer 2.

HTH

Rick

HTH

Rick