Catalyst 3650 changes in OS regarding using ARP to find IP route

[i.hughes]

We recently upgraded a Catalyst 3650 from 15.2-2E6 (3.6.6E) to 16.3.9

now in the old version we did not need to configure the default route, and it found the route via ARP requests, now with 16.3.9 this is no longer the case and configuring the default route now seems to be required.

Is this change of operation documented anywhere? I have had a quick look in release notes but can't find anything

[marce1000]

>now in the old version we did not need to configure the default route, and it found the route via ARP requests

 - I find this a strange statement to say the least. Any default route is decided by the network administrator and can't be known (by definition) by the switch or something else.

 M.

[Mark Malone]

Hi

yes find that very hard to believe an upgrade would remove generic statements or that you could route without a default or gateway , there is no feature diff between those versions like that both ios-xe

if it found it by arp it has to be same subnet as you dont need to route in same subnet  , if its outside subnet needs a route , thats how it works

[i.hughes]

Hi Mark,

I think you are under the same impression as I was, that you always need a default gateway or Ip route configured.

But that is not always the case some Switches and OS versions  don't, they rely on the switch doing an ARP request to the router( or L3 Switch)  By default proxy is enabled on the routers and L3 switches so they will resolve the route for the L2 switch

see the link below.

https://community.cisco.com/t5/routing/proxy-arp/td-p/1560798

[pieterh]

maybe your setup depended on proxy-arp instead of just arp?

-> proxy arp should be enabled by default -> check if this still is

[i.hughes]

As far as I am aware the L3 switches have proxy arp enabled by default, so
when the L2 switch sends the arp request the L3 answers
The proxy arp is not on the L2 switch ( correct me if I am wrong)

[i.hughes]

HI M
you missed the point. Yes you can configure a default route with the ip
default-gateway command, but some switch OS don't need this as they use
ARP requests to find the route.
my question is what release of OS did this change, so no longer id an ARP
request