Comments on: Key Players

By: Ed Harmoush

Ed Harmoush — Sat, 15 Oct 2022 00:09:33 +0000

Almost… except, the destination IP of the gateway will not be used. THe destination IP will still be the end host of the communication. More details here: https://www.youtube.com/watch?v=JI9Zm2tbUoE

By: Ed Harmoush

Ed Harmoush — Sat, 15 Oct 2022 00:05:22 +0000

In reply to Phat Tran.

The host is configured with only one default gateway — this is the IP they are ARPing for. If that IP only exists on one L3 switch, than only that one will answer. IF the IP is being shared by the L3 switches (as in HSRP or VRRP or something) then either L3 switch can/will respond with the virtual MAC address of the shared IP address. More details on L3 switches here: https://www.practicalnetworking.net/stand-alone/routing-between-vlans/

By: Lalit Sharma

Lalit Sharma — Wed, 21 Sep 2022 18:39:26 +0000

For below point When a Client is attempting to speak to a host in a foreign network, the Client will issue an ARP request for the Default Gateway’s MAC address. I guess first ARP request will be generated with destination IP of gateway and once we have the MAC of gateway then it will construct further packets with actual IP as destination

By: Phat Tran

Phat Tran — Tue, 06 Sep 2022 02:31:24 +0000

In reply to Ed Harmoush.

Dear Ed,

In case of different subnet, host will ARP for Default gateway’s unknown MAC address. What issues if host connects to L2 switch and L2 switch connects to two L3 switches. I mean that host issues ARP for default gateway to both L3 switches. What happen then?

Thank you very much.

By: Ed Harmoush

Ed Harmoush — Tue, 17 Aug 2021 16:28:30 +0000

In reply to chan.

Sure! I discuss Broadcasts in great detail here:
https://www.practicalnetworking.net/stand-alone/local-broadcast-vs-directed-broadcast/

By: Ed Harmoush

Ed Harmoush — Tue, 17 Aug 2021 16:27:46 +0000

In reply to David.

Hub / Switch can only be considered hosts if you are sending traffic TO the hub/switch. Otherwise, correct, they are not considered host.

Hosts and Routers are actually more similar than you think. I discuss the explicit difference in this video:
https://www.youtube.com/watch?v=AzXys5kxpAM

By: David

David — Tue, 17 Aug 2021 15:39:51 +0000

From what I understand a Hub, Switch and Router are not considered Host. Correct?

By: rishi kumar sahu

rishi kumar sahu — Sat, 03 Jul 2021 12:14:28 +0000

this is really very simple and great explanation .

By: Ed Harmoush

Ed Harmoush — Sun, 22 Nov 2020 02:59:09 +0000

In reply to asuka. Great question. A client knows it's own IP and it's own Subnet Mask, therefore it can do a little subnetting to determine what other IP addresses are on it's own network. If the target host is in that range, it knows it is speaking to a host in the same network. If the target host's IP address is not in that range, then it must use the Default Gateway.

By: asuka

asuka — Thu, 19 Nov 2020 12:04:08 +0000

“When a Client is speaking to a host in the same network, it will ARP for the MAC address of the host.”

How does the client know if the destination host is in the same network?
Does it always apply a subnet mask of 255.255.255.0 to figure this out?