Extended Host Mode

[TJ - Networking]

Hello,

   I'm using Catalyst 3850 running 16.3.8.

   I was curious exactly what "Extended Host Mode is enabled" gets me. It seems to me as though it allows switching as normal and static routing.  In order for me to gain access to routing protocols like OSPF, RIP, etc I need to enable ip routing.  

  Can anyone confirm exactly what I get with Extended Host Mode on a 3850?  I've noticed for instance that static routes are not available on an older 2960-CX running 15.2;  static routes hold no sway unless I enabled ip routing. On my 3850 if I add static routes they show up when I do a show ip route and are indeed routing based on those configurations, ip routing is not enabled.

Thanks for any insight.

[balaji.bandi]

As per the document here is the one :

Netflow IPv6 Exporter/IPv6 Extended Host Mode: This feature enables FNF Export over IPv6.

Regarding ip route will be available base license. you should be able to add static routes.

[Hector Gustavo Serrano Gutierrez]

Hi @TJ - Networking,

You are right. On the Catalyst 3850 (and 3650) family of Switches, even with no ip routing in place, the show ip route command will show you Connected and Static routes. This behavior differs from other families of Catalyst Switches.

This "Extended Host Mode" is basically needed on this platforms to internally make the device use CEF forwarding to figure out how to transmit packets generated internally. I believe this is required for certain features like CAPWAP tunnels since this device has an embedded internal WLC (Wireless LAN Controller).

Still, you must have ip routing enabled to use Routing Protocols and even when just using Static routes as usual.

Here how the message is shown with 'no ip routing' in place.

Switch3850#show ip route
Extended Host Mode is enabled
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
. . .

 Hope this helps.

Regards.

[paul driver]

Hello

Just like to add - What SDM template is applied to the switch, only the advanced template will allow routing?

Show sdm prefer

[TJ - Networking]

The SDM template applied is indeed the advanced template.

[TJ - Networking]

Mr. Gutierrez,

   So, just to confirm. Within the 3850/3650 family the Extended Host Mode essentially allows for internally generate traffic access to the 'routing' that shows by using show ip routing command.

   Knowing this would it explain the following:

   I have 2 subnets on my 3850. 172.24.1.0 and 192.168.1.0.

   My default gateway of last resort is 192.168.1.1. (set via ip default-gateway 192.168.1.1)  

   My ntp is provided through the 172.24.1.0 network, with a gateway there of 172.24.1.1.  By adding the following static route:

       ip route 10.1.2.50 255.255.255.255 172.24.1.1  (10.1.2.50 is my ntp source)

   I was able to get NTP updates without ever enabling ip routing.

Thanks

[Hector Gustavo Serrano Gutierrez · Accepted solution]

That's correct.

Still, I'd suggest you to enable ip routing. The main reason is that the reception of ICMP redirects (if any) can create entries in your routing table in this mode.

Regards.