May I use any VLAN interface IP address as Default Gateway ???

shivgahlot · ‎07-13-2007

I have so many vlan & vlan interface in my network, now suppose I am sitting in vlan 2 & using vlan-2 interface IP address as default gateway & working fine.

Now I change my default gateway & give vlan-3 Interface ip address as default gateway. Again I can reach every where in my network & internaet. Configuration is given below :-

interface Vlan2

description *** For Servers ***

ip address 10.2.100.1 255.255.0.0

standby 2 ip 10.2.0.1

standby 2 priority 110

standby 2 preempt

!

interface Vlan3

description *** For Labs ***

ip address 10.3.100.1 255.255.0.0

standby 3 ip 10.3.0.1

standby 3 priority 110

standby 3 preempt

!

Please suggest where I am making the mistake buddy ???

smothuku · ‎07-13-2007

Hi ,

switch you are using supports IP routing...

I guess Intervaln routing is been done on the switch...

which switch u are using in network ...

Note : you can reach anything in network if you are in correct vlan...suppose if your pc is configured ip address of 10.2.100.2 and gate 10.2.100.1 and it is connected to switch port which is in another vlan you cann't reach anything in network...

Cheers :)

satish

Jon Marshall · ‎07-13-2007

Hi

What vlan is your PC allocated to ?

Jon

Richard Burts · ‎07-13-2007

If I understand the original post correctly he is in VLAN 2 and then configured the PC with default gateway using the address of the VLAN 3 interface. This can work ok given 2 requirement:

- first the obvious one - that intervlan routing is enabled.

- then the not obvious one - proxy arp must be enabled.

I believe that what is happening is that the PC is configured with a "remote" address as its default gateway. It ARPs for the gateway address. The VLAN 2 interface receives the ARP request for the remote address, and if proxy arp is enabled then the interface will respond to the arp request with its own MAC address. Proxy ARP is enabled by default. I suspect that if they turn off proxy arp that the gateway in VLAN 3 will no longer work.

HTH

Rick

HTH

Rick

Jon Marshall · ‎07-13-2007

Hi Rick

"If I understand the original post correctly.."

One thing i have learnt from you on this forum is that it's not wise to make assumptions :) so i just wanted to clarify before responding.

Jon

Richard Burts · ‎07-13-2007

Jon

Yes indeed, as a consultant I keep being reminded that assumptions about customer networks can be dangerous. It is never a bad idea to clarify assumptions before responding.

In this case I was fairly comfortable with the assumption and thought that the assumption led to an interesting scenario which would be interesting to discuss. If it turns out that the PC is not in VLAN 2, then we will need a different discussion. But I thought that the operation of proxy ARP was something that some people would not be familiar with and was worth the mention.

HTH

Rick

HTH

Rick