Routing or switching issue?

[Andrew White]

Hello,

None of us can work this out.

I wonder if it's the 4 hour ARP ageing?

So we have a remote site with a single Cisco 3850 with a few devices plugged in and 2 x Cisco IE2000 switches trunked to the 3850. 

All 3 switches have default gateway that points to 192.168.1.1 using 'ip default-gateway 192.168.1.1' which is the WAN providers router.

Last week we changed WAN providers and moved the WAN port in the 3850 from the current router to the new one and we lost access to all the Cisco switches remotely via ssh and could no longer ping them.  However a chap on that LAN could ping them.

I asked him to add an 'ip 0.0.0.0 0.0.0.0 192.168.1.1' as this is a L3 switch and we could then ping the switch and access it remotely.  The other 2 switches are L2 so we couldn't add that command and had to roll back.  Also while we were on this new WAN link it was extremely sluggish.

We have done 5 sites before this that are exactly the same on our side, however the WAN provider did say this was a little different to the others from there side but confirmed all is good and it's not them.

So I'm a little stumped now.

I wonder if we should clear the ARP or set the ARP ageing to 5mins as it currently 4 hours by default? so it gets the new IP.Mac mapping?

Thanks

[balaji.bandi]

If the Switch only Layer 2 and externding with provider Layer 2, defaul-gateway should work for you.

yes since new Gateway changed that retain in MAC Address tables. worth clear ARP entry when ever you move to new provider, test 2 or 2 Layer 2 switch and see how it goes.

[paul driver]

Hello

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@Andrew White wrote:

Hello,

None of us can work this out.

I wonder if it's the 4 hour ARP ageing?

So we have a remote site with a single Cisco 3850 with a few devices plugged in and 2 x Cisco IE2000 switches trunked to the 3850. 

All 3 switches have default gateway that points to 192.168.1.1 using 'ip default-gateway 192.168.1.1' which is the WAN providers router.

Last week we changed WAN providers and moved the WAN port in the 3850 from the current router to the new one and we lost access to all the Cisco switches remotely via ssh and could no longer ping them.  However a chap on that LAN could ping them.

I asked him to add an 'ip 0.0.0.0 0.0.0.0 192.168.1.1' as this is a L3 switch and we could then ping the switch and access it remotely.  The other 2 switches are L2 so we couldn't add that command and had to roll back.  

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Can you confirm the role the L3 switch is performing?

Naturally if you swap ISP providers the public addressing is changed however it seems the new isps lan facing interface addressing didn't change and it was/is also performing NAT on your behalf because you state the two L2 switches and the one L3 switch all have the same DG of the Old/New ISP lan subnet.

Question is do you really require L3 routing on the L3 switch or can this become a host switch of the ISP Lan subnet just like the other two if so you need to disable ip routing on that switch and just use a D/G

[Andrew White]

Hello,

The L3 switch is really performing like L2 switch, we just point the 3 switches gateways to the WAN router.

[paul driver]

Hello

So disable  ip routing (no ip routing) on that "L3" switch and on the other switch's if its enabled, and just use default-gateways

[Andrew White]

Why would that make a difference though, the switch is .11 and all 3 switches point to .1 for their gateway which is the router and are working fine, it’s not until we swap the WAN router to the other WAN provider do we lose access to the Cisco switches and cant ping them, but can ping all other devices on the same subnet that use .1 as their gateway.

[paul driver]

Hello

The difference is the downstream devices when ip routing IS disabled ( the other switches) wont rely on the l3 switch and ONLY the "L3"switch now a "L2" switch can route for itself just like any ip host (pc/server) etc...and not for the other switches and for management purposes only an D/G for all switches ONLY required