Unanswered Question
Aug 24th, 2007

Hi all, can anyone tell me about typical encapsulation, say ppp, does it only encapsualtion the ip header and data within the ethernet frame, or does it encapsulate the ethernet frame ?

I have this problem too.
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thomas.anthony Fri, 08/24/2007 - 03:15

PPP encapsulation is defined in RFC 1661; please check that for all the information

mohammedmahmoud Fri, 08/24/2007 - 03:37

Hi Carl,

The router adds the appropriate layer 2 header to encapsulate the IP packet before it is sent out of the appropriate interface according to the encapsulation of the outgoing interface with no relation to the input interface (if the routers is running CEF the adjacency table should be responsible about this).

Cisco-2821#sh adjacency detail

Protocol Interface Address

IP Serial0/1/0 point2point(7)

0 packets, 0 bytes


CEF expires: 00:02:39

refresh: 00:00:39

Epoch: 0

IP GigabitEthernet0/0

28 packets, 3555 bytes


ARP 04:02:22

Epoch: 0

IP GigabitEthernet0/1

0 packets, 0 bytes


ARP 00:52:40

Epoch: 0


Mohammed Mahmoud.

CSCO10892433 Fri, 08/24/2007 - 03:46

Hi, carl

Normally ppp only encapsulate Layer3 packets (like ip packets). Unless you are doing some advanced feature like l2tpv3 tunnel, ppp won't encapsulte the whole ethernet frames because they are in the same layer.



carl_townshend Thu, 09/06/2007 - 08:52

so over ppp serial link, what is the frame type changed too ? is the layer 2 properties now a ppp frame and not ethernet ?


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