Routing Issue (ARP)

[bikramchowdhury]

Hi All,

Please provide me all the possible solution.

Scenario is like:

User connected to access switches (3560)=> connected to Core L3 switch (3750) (IP=10.10.10.3)

3750 is connected to two ISP=> ISP 1  (Inside IP 10.10.10.1) and ISP 2 ( Inside IP 10.10.10.2)

My IP address of Machine is 10.10.10.12 subnet mask 255.255.255.0 , default gateway=10.10.10.1

Issue is : 

When my default gateway of machine is 10.10.10.1 (ISP-1) then the internet is working fine.

but when i keep my default gateway of machine 10.10.10.2, then some time it works and sometime it does not work.Generally not working.

provide the solutions if you have faced. Below is the configuration:

For Core  L3:

interface Vlan10
 ip address 10.10.10.3 255.255.255.0
 no ip redirects     ( Is this required)
 no ip unreachables     ( Is this required)
 no ip proxy-arp     ( Is this required)
 ip route-cache policy      ( Is this required)
 arp timeout 300     ( Is this required)

ip route 0.0.0.0 0.0.0.0 10.10.10.2 (ISP2)

Any traffic coming to Core L3 will go to ISP2. But if we change the default gateway of machine 10.10.10.12 to 10.10.10.1 (ISP-1) then it should go via ISP 1 then internet is working fine and if change the default gateway of machine to 10.10.10.2 then issue comes. Any idea or suggestion ? 

Rest all reachablity is working fine.

========================================================

[Elektordi]

Hello,

I see you are using "ip route-cache policy". Do you have PBR enabled on your device?

And is the NAT managed by the ISP devices? If yes, all you TCP sessions may have to reset on ISP failover.

Best regards,

Guillaume

[bikramchowdhury]

Hi Guillaume,

PBR is enabled for another VLAN and not for 10.10.10.X. Shall I remove the same.

Also the nat is managed by ISP device. ISP failover is not not set. If one ISP gets down then the default gateway have to be changed on Proxy server to switch the ISP.

Also kindly let me know what I can do further.

Regards,

Biks

[e.ciollaro]

Hi Biks,

I think the problem is not due to the Core switch or at least not to its Layer 3 functions, in fact your  machine (I mean host 10.10.10.12)  is on the same subnet of its default gateway (10.10.10.1 or 10.10.10.2)  so Core switch does not route packets sent by 10.10.10.12.

Host 10.10.10.12 can ping 10.10.10.2 ?  ARP Table for 10.10.10.2 is correct ?

Could you post interf config of 3560 switch connecting your host to vlan 10, config of interf connecting 3560 and 3750 (for both switch) and config of 3750 interf connecting ISP-1 and ISP-2 ?

enrico