As each host transmits the table becomes accurate What if a node moves Table

As each host transmits the table becomes accurate

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As each host transmits, the table becomes accurate What if a node moves? Table aging u Associate a timestamp with each table entry u Refresh timestamp for each new packet with same source u If entry gets too stale, remove it 16 Host A B C D W X Y Z Port 1 1 1 1 2 2 3 2 CSE 123 – Lecture 7: Bridging
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Learning Example Suppose C sends frame to D and D replies back with frame to C CSE 123 – Lecture 7: Bridging 17 C sends frame, bridge has no info about D, so floods to both LANs u bridge notes that C is on port 1 u frame ignored on upper LAN u frame received by D
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D generates reply to C , sends u bridge sees frame from D u bridge notes that D is on port 2 u bridge knows C on port 1, so selectively forwards frame via port 1 18 Learning Example CSE 123 – Lecture 7: Bridging
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Learning Bridges Recap Each bridge keeps a list mapping link-layer destination address to port number u (what are the directions to this destination?) This list is populated by looking at the source address of each packet it receives on a given port and entering those values in the table u (if a packet from A came from port x , then packets to A should be sent on part x ) If a frame arrives with a destination address not in the table, then send on all ports (except the one it came on) CSE 123 – Lecture 7: Bridging 19
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For next time… Keep reading 3 – 3.1 CSE 123 – Lecture 7: Bridging 20
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  • Fall '08
  • Varghese,G

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