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ospf link failure

In the lecture for link state routing, why can't we pass to X5 a packet to A1? We could imagine X5 forwarding it to X3 and X3 forwarding it to A1. I know it is not optimal, but it seems to work.


Good luck for tomorrow.

Ghita Mezzour
Posted by Ghita Mezzour at 15:32
Comments (1)
Exo 4.4 Q2
Exo 4.4 Q2
What is the definition of line utilisation.

Posted by Ramatou Abibou at 12:34
Comments (1)
Exo 4.3 Q2
I have a problem with question 4.3.2. The question is: is there a case where the first option bit should be considerded as an error? The answer says that in some cases, you need to set the option bit to 1. I don't understand the connection. Could you develop the answer please?
Posted by Ramatou Abibou at 12:08
Exo 4.2 Q5
Exo 4.2 Q5

Why the maximum size of the ip datagram is 2^16

is it total lenght is coded by 16 bit
Posted by Ramatou Abibou at 10:34
Comments (1)
Test1,2,3 and the solutions
Hello, is it possible to have the assignments of the Test that we have done during the semester and their solutions?
Posted by Maoan Zhou at 14:27
Comments (3)
Lab and test 3 grades?

I just wanted to know if it would be possible that you post all the tests and lab notes on the site with our sciper or if not tell us when they'll be available in front of your office.

Thanks alot,

Posted by Christophe Gudin at 19:08
Comments (1)
Last set of questions
Hi, some last questions (I hope):


Why is link L8 on B3 listed as "designated" ? Links L7 and L8 are on the same LAN, so, only one link can be designated, the other one should be backup, shouldn't it ?


I don't understand what the forwarding address field in an AS-external-LSA represents and what is it used for.
- Is it the address of an AS boundary router in another AS ? But this information is useful only to the AS boundary router which originated the LSA, so why inform every one of it ?
- Is it the address of the router, in this AS, toward which traffic had to be send to reach the network described in link state id (in LSA header) ? But in this case, the forwarding address will always be the same as the advertising router (unless AS boundary router advertise routes to a linked AS through another AS boundary router).
In the example on p.73, the forwarding address is set to, what does this value means ?
- Is it to describe a default route ?
- Is a special value which means "advertising router" ?

Router announce an infinite distance to AS boundary router which is the same router. So announce an infinite distance to itself ! Is it correct ?
Posted by René Giller at 18:38
Comments (2)
Office hour for questions on the midterm

is it possible to get a possibility to ask some questions on the midterms?
In my case, i got a question on the first part of question 2 in midterm 2.
I was allready present during the office hours, but i was told that you(the assistants) would announce a kind of "question hour" where alle of the assistants would be there to answer on questions.


Posted by Johann Töws at 12:08
appli.ppt / ipagain.ppt
Hi, I, again, have some questions:

If I'm not mistaken, a TCP server port is a port on which a machine listen for incoming connections. So, In passive-mode, why is port 1515 on S not listed as such ? And, always in passive-mode, the OK arrow of the second connection is reversed, I think.

p.13, 3.
It is said that a root name server knows the IP addresses of all level-2 domains. But there's a lot of level-2 domains ! So is it not all top-level domains ? And then, another name server which knows all level-2 domains related to this top-level domain gives the final answer ?
And how is the database of these top-level (level-2) domains maintained up-to-date at a root server ?

R1 sends an ICMP redirect to inform A that a shorter route exists through R2. Ok, but how does R1 knows about the connection A-R2 ? R1 being on link with A and R2 doesn't automatically imply that A and R2 are also on link. So, does the ICMP redirect function only with certain network topologies ?

When PMTU is enabled, isn't the "don't fragment" flag set ? Is this case, a router cannot fragment a TCP packet even if the PMTU estimation failed, all it can do is send an ICMP message to inform that the packet is too big.

In this slide, the physical address seems to be deducted from the IP address, but where does this 33:33 comes form ? Is it just a default value set when some part of the physical address can't be deducted.
The solicited-node address ff02::1:80b2:9c26/128 corresponds to a machine which has a physical address ending by 80.b2.9c.26. This doesn't correspond to lrcsun13' physical address but it does correspond to the translated IP address of lrcsun13. So, will lrcsun13 reply to ff02::1:80b2:9c26/128 ?

Ok, it's all for tonight.
Posted by René Giller at 15:50
Comments (3)
tp4 experiment 4

We tried to run after_restart.sh as written in the tp4 document, but there is no /proc/sys/net/ipv4/tcp_congestion_control on any of computers we tried. What should we do?

Posted by Aleksandar Dragojevic at 21:47
Comments (2)
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