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New Member

Need help with this routing issue

Hi Experts,

Would like to get assistance on the following issue that i'm currently facing.

I have the setup as follows:

Internet --------------> Router --------------------> SWitch ---------------> Hosts

Router is acting as the default gateway and has an address of 10.10.192.1/21

Behind the router i have 6 switches and behing each switch I have hosts and the switch is acting as a dhcp server for the hosts.

on the switches i have the following configuration:

ip dhcp pool 1

    network 10.10.193.0 255.255.255.0

    domain-name <somename>

    dns-server <somename>

    default router 10.10.192.1

int vlan 1

    ip add 10.10.193.1 255.255.255.0

The hosts receives the ip from via dhcp but unable to ping the default gateway 10.10.192.1 ??

Am  i missing something here?

Please advice...

Thanks,

-Vijay

12 REPLIES
New Member

Need help with this routing issue

Hi Vijay,

Are you able to ping the Router' Lan interface from the switches?

New Member

Need help with this routing issue

No.. I'm not..

-Vijay

New Member

Need help with this routing issue

Is IP routing enabled on the switches?

If not, how about;

conf t

ip default-gateway 10.10.192.1

end

?

New Member

Need help with this routing issue

adding ip default-gateway 10.10.192.1 didn't help.

Would adding a static route help

-Vijay

Cisco Employee

Need help with this routing issue

Hi Vijay,

Hosts need to have default gateway in same subnet as their ip. So I guess it should be 10.10.193.1. Becuase end host will send ARP broadcasts to resolve default gateway ip to MAC address. Those broadcasts local to subnet and will never reach router.

So you need to change default GW to 10.10.193.1 and configure routing on siwtch to route traffic sent to internet to 10.10.192.1 towards your router.

Nik

New Member

Need help with this routing issue

Thanks Nikolay, oversaw the 192 :-)

New Member

Re: Need help with this routing issue

Thanks Nikolay. That perfectly makes sense from the default-route configuraiton on the ip dhcp pool.

Would adding a static route on the switch help?

ip route 0.0.0.0 0.0.0.0 10.10.192.1? I guess the default-gateway also does the same job?

-Vijay

Message was edited by: Vijay Swaminathan

Cisco Employee

Need help with this routing issue

Hi Vijay,

Can you please also confirm there is a route configured on the Router for the echo reply packets .

Regards,

Prajul.

New Member

Re: Need help with this routing issue

Hi Prajul,

Router and switch are connected back to back.

Router (10.10.192.1/21) connected to switch (10.10.194.1/24)

so since 10.10.194.1/24 is a subnet inside the network 10.10.192.1/21 I guess it should not be a problem for the router to reach this..

my concern is how does switch reach router?

please advice if I'm incorrect.

Thanks

-Vijay

Cisco Employee

Re: Need help with this routing issue

Hi Vijay,

Can you please check the reachability of the router IP "10.10.192.1" from the switch. It seems like since the switch output port ( i assume the port is confgured as a L3 port ) is in a "/24" subnet it may not see "10.10.192.1"

we may need to

     - either make both these interfaces on the same subnet ( so switch interface can see the  router subnet )

     - Configure a static route to the router IP as going via the switch interface

               "ip route 10.10.192.1 255.255.255.255

Kindly let me know if I'm missing something.

New Member

Re: Need help with this routing issue

Hi Prajul,

I have configured a SVI on the switch with an address 10.10.194.1 with the same mask /21, i'm able to ping the default gateway 10.10.192.1. However i was unable to reach internet .

I had ip default-gateway 10.10.192.1 configured but that did not work. when I configured a static route on the switch then that worked

I still don;'t know why the "ip default-gateway 10.10.192.1" didn't work

-Vijay

Cisco Employee

Re: Need help with this routing issue

Hi Vijay,

Can you please paste the config ( with the dafault-gateway configuration ) which is failing

Thanks and Regards,

Prajul.

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