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From: leong@ANDREW.CMU.EDU (John Leong)
Newsgroups: mod.protocols.tcp-ip
Subject: Re: Re: IEEE and Ethernet
Message-ID: <MS.leong.0.leong.248.0@andrew.cmu.edu>
Date: Tue, 8-Jul-86 18:40:36 EDT
Article-I.D.: andrew.MS.leong.0.leong.248.0
Posted: Tue Jul  8 18:40:36 1986
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Noel,

Re :

>> How do you do address translation? 
>> I.e. where does the code that creates the LLC header 
>> get the 48 bit address from to go with a 32 bit IP address?	

The LLC header is encapsulated by the MAC layer (or "hardware" layer) header.

The LLC header consists of a one-byte DSAP, one byte SSAP and a one byte control
field. There is no 48 bit address in the LLC header.

[The DSAP and SSAP has the value of 6 for the IP/TCP family of protocol. The
control field has the value of  3 for UI : Un-numbered I-frame.]

Encapsulated inside the LLC header is the IP or ARP packet.

May be the 48 bit address you refered to is the 48 bit address in the MAC (802.3
Ethernet or 802.5 Token Ring) layer header. In which case, the IP (32 bits)
to MAC (48 bits) layer address mapping is done by ARP is per Plummer's algorithm.

Leong