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CCNA Q.

Started by icecream-guy, July 21, 2017, 09:29:17 AM

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icecream-guy

July 21, 2017, 09:29:17 AM
Which is is correct default gateway for Host A?   is it 192.168.1.2 or 192.168.1.1?  and why?
:professorcat:

My Moral Fibers have been cut.

dlots

#1
July 21, 2017, 10:32:21 AM Last Edit: July 21, 2017, 11:14:43 AM by dlots
[spoiler]
Is S-A a L3 switch?  If so it could be either
If it's not R-A as it's layer 3 and can route traffic between the interfaces.

deanwebb

#2
July 21, 2017, 10:40:55 AM
At first, I wondered why ristau was asking such a question, and then I thought maybe it's because he didn't want answers from the experienced guys... But I'll put mine in and use spoiler tags...

Because I'm cool like that...  :smug:

[spoiler]Which of those is connected to the Internet? If that's a L3 switch doing all the routing to the Internet and stuff and the router is there for just one connection to a stub site, then the switch is the default gateway.

If the switch is L2 and the router does all the srs bsns, then the router is the default gateway.[/spoiler]
Take a baseball bat and trash all the routers, shout out "IT'S A NETWORK PROBLEM NOW, SUCKERS!" and then peel out of the parking lot in your Ferrari.
"The world could perish if people only worked on things that were easy to handle." -- Vladimir Savchenko
Вопросы есть? Вопросов нет! | BCEB: Belkin Certified Expert Baffler | "Plan B is Plan A with an element of panic." -- John Clarke
Accounting is architecture, remember that!
Air gaps are high-latency Internet connections.

icecream-guy

#3
July 21, 2017, 10:57:55 AM
shouldn't matter if the switch is L2 or L3, the Assigned ip address "I will say, switch management ip address" is on the same 192.168.1.0/24 network and vlan 10
:professorcat:

My Moral Fibers have been cut.

matgar

#4
July 23, 2017, 01:42:08 AM
The simple answer (for CCNA level) is of course Router A.
The more complex answer is that if the Switch is a L3 it could just as well be the default gateway.
But for this scenario with vlan 10 extending to the Router and with it being a CCNA level Q the expected answer would be Router A.

icecream-guy

#5
July 27, 2017, 06:34:34 AM
Q2

So  if host A has a gateway of the switch vlan 10 management interface 192.168.1.2, and it has a need to send a packet to the router 192.168.1.3

When host A send out a broadcast looking for 192.168.1.3, which device answers? (seen in broadcast "who has IP 192.168.1.3")
Switch or Router?
:professorcat:

My Moral Fibers have been cut.

SimonV

#6
July 27, 2017, 07:50:00 AM
Q3

If host A has switch A as the default gateway, and the packet gets routed out via Router A, which device delivers the return traffic to host A?

deanwebb

#7
July 27, 2017, 08:44:55 AM
Q4

When a packet is routed outbound from the router, what will be the source MAC address? Why?
Take a baseball bat and trash all the routers, shout out "IT'S A NETWORK PROBLEM NOW, SUCKERS!" and then peel out of the parking lot in your Ferrari.
"The world could perish if people only worked on things that were easy to handle." -- Vladimir Savchenko
Вопросы есть? Вопросов нет! | BCEB: Belkin Certified Expert Baffler | "Plan B is Plan A with an element of panic." -- John Clarke
Accounting is architecture, remember that!
Air gaps are high-latency Internet connections.

dlots

#8
July 27, 2017, 09:17:30 AM Last Edit: July 27, 2017, 09:22:30 AM by dlots
Quote from: deanwebb on July 27, 2017, 08:44:55 AM
Q4

When a packet is routed outbound from the router, what will be the source MAC address? Why?

[spoiler]
Trick question: The packet will never be routed outbound as there is no where for it to go.  The packet destined for another subnet will be dropped unless there is a loop-back in which case it will go to the control plane, not routed out. It could also get routed out if there were a static route point to either 1.3 or 1.2.  If that static route points to 1.3 it will probably get dropped, if it's pointing to 1.2 and 1.2 has a gateway of 1.1 then the packet will go between the 2 till the TTL runs out.  The MAC source would be e0 on the router... at least I think the switch would forward the traffic back to the router... now I want to lab this.

Dieselboy

#9
August 06, 2017, 01:20:32 AM
If the pc default gateway is the switch and to get to the destination, the switch has to route to the router on the same subnet, then the pc will be redirected to the router. It's worth remembering this for troubleshooting. Because you could be making routing changes on the switch and not see any affect because the pc is sending traffic to the router directly.

SimonV

#10
August 08, 2017, 06:51:03 AM
Quote from: Dieselboy on August 06, 2017, 01:20:32 AM
If the pc default gateway is the switch and to get to the destination, the switch has to route to the router on the same subnet, then the pc will be redirected to the router. It's worth remembering this for troubleshooting. Because you could be making routing changes on the switch and not see any affect because the pc is sending traffic to the router directly.

That's due to IP Redirects and only if it's enabled on both the L3 device and the client system. I have only ever seen this once and it was on a Unix system. I believe it's also best practice to turn it off on your L3 interface with "no ip redirects".
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