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Community Member

Can't ping interface, please advise

I have 2851 with 2 subinterfaces on g0/0   g0/0.1   10.8.x.x    255.255.0.0   encapsulation dot1q 1

                                                                    g0/0.2   10.6.x.x    255.255.0.0   encapsulation dot1q 2

A 4948 is directly connected to g0/0 interface.Trunking is enabled on the switch interface.  I can ping g0/0.1, but I cant ping g0/0.2.  Can anyone tell me why.  This has stumped me.  The default gateway on the switch is the g0/0.1 ip.  I should still be able to ping both, correct?  Please help.

1 ACCEPTED SOLUTION

Accepted Solutions

Re: Can't ping interface, please advise

I know this is sort of obvious, but usually issues like this are due to a fundamental oversight.  Did you run 'no ip routing' on the switch?  You may need to ensure that the switch is not attempting to route and is working strictly in Layer 2.

20 REPLIES
Cisco Employee

Re: Can't ping interface, please advise

Hello,

What is the native vlan? Do you have a corresponding interface for VLAN 2 on the 4948 side?

Regards,

NT

Community Member

Re: Can't ping interface, please advise

The native vlan is the 10.8.x.x vlan.  I have added the other vlan to

the vlan pool on the switch  The machines connected to the switch can ping 10.6.x.x, but the switch in the cli cant ping 10.6.x.x

Cisco Employee

Re: Can't ping interface, please advise

Hello,

Can you please try to trace the path from the switch to 10.6.x.x address?

Also, on the switch, can you please verify that there is no other VLAN

interface with conflicting address for 10.6.x.x subnet?

show ip interface brief | exc unas

Regards,

NT

Community Member

Re: Can't ping interface, please advise

If I do a traceroute from the cli on the 4948 to the directly connected sub interface address on the 2851, i get :

1***

2***

3***

4***

5***

and so on.

Cisco Employee

Re: Can't ping interface, please advise

Hello,

On 4948, can you issue "show run | include ip rout" and see if the switch has ip routing enabled. If it is, then please make sure that you have a default route (ip route 0.0.0.0 0.0.0.0 10.8.1.1) on the 4948. If the 4948 does not have "ip routing" enabled, then make sure that you have configured "ip default-gw" on the 4948.

Hope this helps.

Regards,

NT

Community Member

Re: Can't ping interface, please advise

The dafault gateway is set. the command shows "no ip route-cache cef" and "no ip route-cache"

Cisco Employee

Re: Can't ping interface, please advise

Hello,

If you have configured the switch as a L3 device (ip routing enabled), then

as John said, please issue a static default route (default gateway will work

only when the device has single l3 interface and ip routing is turned off).

If you want it to be a single L3 interface device, then you can turn off the

IP routing as well.

Hope this helps.

Regards,

NT

Hall of Fame Super Blue

Re: Can't ping interface, please advise

Earl

Is ip routing enabled on the 4948 ? If so can you add to the 4948 -

ip route 0.0.0.0 0.0.0.0

Jon

Hall of Fame Super Blue

Re: Can't ping interface, please advise

Earl

Just a quick follow up to this. The 4948 is a L3 switch. Is there a reason you are using subinterfaces on the router rather than configuring L3 vlan interfaces on the 4948 ? Subinterfaces on a router are only really used nowadays when the switch is only L2 capable.

Jon

Community Member

Re: Can't ping interface, please advise

That is the only l3 switch on that segment. All layer 2 switches connect to this switch. Is there a better way to do this?

Hall of Fame Super Blue

Re: Can't ping interface, please advise

earlkacin wrote:

That is the only l3 switch on that segment.  All layer 2 switches connect to this switch.  Is there a better way to do this?


Earl

Can't read your attachment but the way to do it would be to route the vlans on the 4948 ie. on the 4948 -

int vlan 1

ip address 10.8.x.x 255.255.0.0

int vlan 2

ip address 10.6.x.x 255.255.0.0

then the 4948 will route between the 2 vlans assuming you have "ip routing" enabled. Then on the port on the 4948 that  connects to the router -

int gi0/1

no switchport

ip address 192.168.5.2 255.255.255.252

on the router remove your subinterfaces and configure gi0/0 as -

int gi0/0

ip address 192.168.5.1 255.255.255.252

then either run dynamic routing protocol between router and 4948 such as EIGRP or simply use static routes ie.

on the 4948 -

ip route 0.0.0.0 0.0.0.0 192.168.5.1

on the router -

ip route 10.6.x.x 255.255.0.0 192.168.5.2

ip route 10.8.x.x 255.255.0.0 192.168.5.2

Jon

Community Member

Re: Can't ping interface, please advise

Ive got about another 20 sub interfaces already configured on the router. I was trying to keep uniform. This wasnt my network before now. Is this the best or only way aside from doing the routing from the switch and not the router?

Hall of Fame Super Blue

Re: Can't ping interface, please advise

earlkacin wrote:

Ive got about another 20 sub interfaces already configured on the router.  I was trying to keep uniform.  This wasnt my network before now.  Is this the best or only way aside from doing the routing from the switch and not the router?

Earl

Do you mean 20 subinterfaces under the gi0/0 interface ?  If so you really should look to migrate this to the 4948. This is what L3 switches are designed for ie inter-vlan routing. Basically using subinterfaces on a router restricts the bandwidth between all your vlans. Really if you have a L3 switch the only traffic leaving the switch should be traffic destined for a remote location.

However this will require downtime so it's up to you really as to whether you want to proceed.

As for the original problem did adding a default-route on the 4948 enable you to ping the 10.6.x.x network ?

Jon

Re: Can't ping interface, please advise

I know this is sort of obvious, but usually issues like this are due to a fundamental oversight.  Did you run 'no ip routing' on the switch?  You may need to ensure that the switch is not attempting to route and is working strictly in Layer 2.

Community Member

Re: Can't ping interface, please advise

Thank you!!!   It works now.  I feel dumb.  Thanks

guys for your help.

Hall of Fame Super Blue

Re: Can't ping interface, please advise

Earl

Slightly confused because both myself and NT both pointed this out ages ago in this thread !

Regardless i would still recommend migrating to the 4948.

Jon

Community Member

Re: Can't ping interface, please advise

Im sorry for any confusion Ive caused you guys.  I was trying to get answers and take my kid to the doctor.  Thank you all for your help
.  Again, Im sorry if I wasnt reading everything in the previous posts thoroughly.  Trying to do too many things at once.

Hall of Fame Super Blue

Re: Can't ping interface, please advise

Earl

No problem, just was a bit confused that's all. Hope your kid is okay.

Jon

Re: Can't ping interface, please advise

No problem, man.

Re: Can't ping interface, please advise

Could you post the following:

  • output of a 'sh vtp status' from the router and the switch

Make sure your VTP mode is 'client' on the switch and 'server' on the router.  Sounds to me that this is your issue.

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