Knowledge checks


Destination-based match+action.  



Destination-based forwarding, which we studied in section 4.2, is a specific instance of match+action and generalized forwarding.  Select the phrase below which best completes the following sentence:

"In destination-based forwarding, ..."




 

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1/7

Generalized match+action.



Which of the following match+actions can be taken in the generalized OpenFlow 1.0 match+action paradigm that we studied in Section 4.4?  Check all that apply.




 

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2/7

What fields can be matched in generalized match+action.



Which of the following fields in the frame/datagram/segment/application-layer message can be matched in OpenFlow 1.0? Check all that apply.




 

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3/7

Match+action in Openflow 1.0.



Consider the figure below that shows the generalized forwarding table in a router.  Recall that a * represents a wildcard value. Now consider an arriving datagram with the IP source and destination address fields indicated below.  For each source/destination IP address pair, indicate which rule is matched. Note: assume that a rule that is earlier in the table takes priority over a rule that is later in the table and that a datagram that matches none of the table entries is dropped.



Question List:
Answer List:
  1. Rule 3, with action send to controller

  2. No match to any rule.

  3. Rule 2, with action drop

  4. Rule 1, with action forward(2)


 

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4/7

Crafting network-wide forwarding using flow tables.



Consider the network below.  We want to specify the match+action rules at s3 so that only the following network-wide behavior is allowed:

  1. traffic from 128.119/16 and destined to 137.220/16 is forwarded on the direct link from s3 to s1;
  2. traffic from 128.119/16 and destined to 67.56/16 is forwarded on the direct link from s3 to s2;
  3. incoming traffic via port 2 or 3, and destined to 128.119/16 is forwarded to 128.119/16 via local port 1. 
  4. No other forwarding should be allowed.  In particular s3 should not forward traffic arriving from 137.220/16 and destined for 67.56/16 and vice versa.

From the list of match+action rules below, select the rules to include in s3's flow table to implement this forwarding behavior. Assume that if a packet arrives and finds no matching rule, it is dropped.

 




 

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5/7

Crafting network-wide forwarding using flow tables (more).



Consider the network below.  We want to specify the match+action rules at s3 so that s3 acts only as a relay for traffic between 137.220/16 and 67.56/16.  In particular s3 should not accept/forward and traffic to/from 128.119/16.

From the list of match+action rules below, select the rules to include in s3's flow table to implement this forwarding behavior. Assume that if a packet arrives and finds no matching rule, it is dropped.

 




 

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6/7

Generalized forwarding.  



What is meant by generalized forwarding (as opposed to destination-based forwarding) in a router or switch?




 

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7/7

We gratefully acknowledge the programming and problem design work of John Broderick (UMass '21), which has really helped to substantially improve this site.

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