Esempio di costruzione delle tabelle TSR

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Esempio di costruzione delle tabelle TSR

• Prof. Ing. Carla Raffaelli

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Example network

• TSR B and TSR D use TSR E as next hop
• TSR A uses TSR B as next hop
• TSR C uses TSR D as next hop
• Each TSR has 3 interfaces

if0
if2
if1
A
if1
B
if0
if0
if2
E
if1
if2
C
D
if0
if0
if2
if1
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Contruction of the TFIB

• When A determines the next hop B it takes a tag
  from its pool for example 100
• TSRA uses 100 as an index in its TFIB and sets
  incoming tag to 100, next hop B and outgoing
  interface if1
• When B determines the next hop E, it takes a tag
  from its pool for example 6

In tag
out tag
Next hop
out int.
On TSRA
100
?
TSRB
if1
In tag
out tag
Next hop
out int.
On TSRB
6
?
TSRE
if1
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Distribution of information

• To define outgoing tag TSRA sends information
  about local binding to B and C
• When B receives binding information notices that
  it doesnt come from Bs next hop. So TSRB doent
  use this information
• When A receives information from B it notices
  that B is next hop and uses the tag to update its
  outgoing tag
• TSRE has itself as next hop and its outgoing tag
  remain ?

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TFIB entries after tag distribution
In tag
out tag
out int.
Next hop
On TSRA
100
6
TSRB
if1

• When E receives packets that carry tag 6 TSR E
  acts as an edge TSR and strips the tag from the
  packet

On TSRB
6
6
TSRE
if1
On TSRC
17
5
TSRD
if2
On TSRD
5
6
TSRE
if0
On TSRE
6
?
TSRE
if0
6
Actual packet forwarding

• When TSRA receives a packet with tag 100, it uses
  this tag as an index to locate the entry
• A replaces the tag carried by the packet with the
  outgoing tag 6 (label swapping) and sends it to B
  via interface 1
• When E receives the packet it strips the tag