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TOPIC: what will be source and destination MAC address

what will be source and destination MAC address 8 years 11 months ago #24587

Hi All,

I'm newbie to this forum and greeting all.
I have a question for you all.

If router A want to send data to router B, what will be the source and destination MAC address.

Router A
Router B
(serial 0/0) (serial 0/0)

I think source MAC should be router A (S0/0) and destination MAC should be router B's S0/0.

Am I wrong?

Some people say that there are no frame when routers are communicating each other.


Thanks and regards
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Re: what will be source and destination MAC address 8 years 11 months ago #24592

  • S0lo
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As far as I know, MAC addresses are only available when you have Ethernet (802.3) as the data link protocol. Serial connections don't use ethernet. Instead, HDLC or PPP or etc... is used. These don't need mac addresses since they are all point to point.

So simply, there are no MAC addresses for either of the s0/0 interfaces.

Hope that helps.
Studying CCNP...

Ammar Muqaddas
Forum Moderator
www.firewall.cx
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Re: what will be source and destination MAC address 8 years 11 months ago #24593

  • Smurf
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I think thats correct also
Wayne Murphy
Firewall.cx Team Member
www.firewall.cx

Now working for a Security Company called Sec-1 Ltd in the UK, for any
Penetration Testing work visit www.sec-1.com or PM me for details.
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Re: what will be source and destination MAC address 8 years 11 months ago #24602

Thanks S0lo and Smurf.

I am clear my confusion. And I have a another question for you all.


Host A----Switch
RouterA(serial s0/0)
(serial s0/0)RouterB
Switch----Host B

when host A send data to host B, how many data encapsulation will be made?
I think
1) Host A to Router A
2) Router B to Host B
so there are two data encapsulation will be made.
Is it correct?

thanks and regards
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Re: what will be source and destination MAC address 8 years 11 months ago #24604

  • Smurf
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Its going to depend on what you mean by Encapsulation.

If you are looking at OSI then each layer encapsulates as it goes down the stack.

At the data link layer, its a point to point connection using MAC addresses. If, at the network layer, if the traffic needs to go to a seperate subnet, at the data link layer a point to point connection is made to the next hop address to then route the traffic. Therefore it goes from Host to Router.

On a serial link, it is using a different Point to Point protocal, if i am not mistaken, the network layer is then encapsulated into the Point to Point Protocol to get sent over the Serial connection, when it is then routed on, it then gets encapsulated using the ethernet datalink encapsulation to get from the router to the destination host.

If that all makes sense (it does in my head, lol)

Take a look at this guide from this website www.firewall.cx/osi-encap-decap.php

To Summaries

From Host A to Router A, it would use Ethernet 802.1 and at the DataLink Layer MAC
From Router A to Router B, it would use what ever encapsulation you are using on the Point to Point link (PPP/HDLC/Frame Relay, etc..)
From Router B to Host B, it would use Ethernet again.

Cheers
Wayne Murphy
Firewall.cx Team Member
www.firewall.cx

Now working for a Security Company called Sec-1 Ltd in the UK, for any
Penetration Testing work visit www.sec-1.com or PM me for details.
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Re: what will be source and destination MAC address 8 years 11 months ago #24605

Thanks for you reply, Smurf.

And how many different frames will the packet be encapsulated when Host A send data to Host B?

1) From Host A to Router A
Frame is encapsulated with destination MAC of Router A.

2) From Router B to Host B
Frame is encapsulate with destination MAC of Host B

But I am not sure that does the frame encapsulated with MAC between Router A and Router B?

I am not very clear this one.

HDLC/PPP/FrameRelay work in DataLink Layer so that does it need to use MAC?

thanks Smurf Again for your knowledge sharing
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