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TCP/IP

midterm 1,2 and tp 1,2 grades
... are shown printed in front of BC 260.
To see your grades you must know your sciper number.

For midterm 1 and 2 you have posibilty to see your work until end of January 2007 at latest - after that date we consider the published grades final.

Any possible mistake for your tp 1 and 2 grades should be reported to us by end of January 2007 at latest - after that date we consider the published grades final.

TAs
Posted by Slavisa Sarafijanovic at 9:32
Different questions regarding the slides
Hi

There are several things I didn't get in the slides, some of them being just typos, I think.


in archi.ppt on top left of page 39, there is the formula T = L/D, shouldn't it be T = L/b ?


in tcp.ppt on pages 43, there are several things I don't understand :
"Reset timers for packets 4, 5, 6", as packet 6 is an ack, shouldn't it be "Reset timers for packets 4, 5" ?

then at event 8, why does the sender waits for the ack (event 9) before sending the next packet ? Is it because it's usable window is empty ?

there is something I don't understand with the "win" field (same on page 57). It is supposed to be the offered Window Size so I suppose that on the acks, it represents the window's size the sender should use (credits). And on the data, it represents the window's size the sender is actually using. So why don't they match ? After receiving an ack, the window's size should be set the the received value, and then the next sent packet should piggyback this same value.


in dv.ppt on page 9, I think there is a typo on the 3rd (should add B4 at the end) and 4th routes (should add B2 between R2 and R3).

on page 36, the statement "Just before B updates its table..." shouldn't it be "Just before B broadcasts its table..." ?

on page 42, I don't understand what the "bounce effect" is. Is it just a synonym for slow convergence ?

on page 43, I think the starting scenario is: link 1 fails -> the system converge to a new stable state -> link 6 fails -> D updates its table (sets costs to INF). Then the entry "B l3 INF" on table D is not logical, is should be : "B l6 INF" (same for pages 46, 47, 48)

Are these statements true ?:
split horizon can fail only if there is a loop;
even if there is a loop, the order of the broadcasts will determine failure or success of split horizon (success if all routers with correct infinite values are able to broadcast their values to all neighbors before receiving incorrect values);
even if split horizon fails, the routers will just count toward infinity, thus (slowly) converging to a stable state.


in bgp.ppt on page 5, it is said that ARD D and B are transit. It's ok for D since it serves as a relay between A and C. But it's not the case for B so shouldn't B be multihomed instead of transit ?

on page 12, the last line states that : "ISP 1 announces to ISP3 only routes to ISP3?s customers". But it doesn't make sense to me, so shouldn't it be "... only routes to ISP1?s customers" ? This way, ISP3 is not aware of the connection between ISP2 and ISP1 and therefore cannot send its packet to ISP2 through ISP1.

on page 20, the import policy accepts or rejects routes. But what is the point of rejecting some routes ? Are there incorrect routes ? And if yes, how can they be detected ?

on pages 34, 35, 79, 80, the address 2.2.2.2 is the external address of router R5 and not R6 ?

on page 80, shouldn't R1 also inject the route in its forwarding table ?
Posted by René Giller at 1:37
Comments (9)
additonal exercise session on jan 11
we will have a look at exercise 3.3 on january 11 -> cf course schedule on the website.
Posted by Manuel Flury at 18:32
TP3 - Changes on TP deadline and in Problem 3
Hi all,
the new dedline for TP3 is on January 11, 2007.
You can hand it in either during the office hours on January 11, or just before the beginning of the lecture, in INM 202, always on January 11.
Please note that the deadline is sharp: reports that are handed in
after will be accepted for grading but 20 points (out of 100) will be taken off. Reports for TP3 will not be accepted after Monday 15 january 2007.
Also, Problem 3 is now an optional part of TP3: if well done, it gives you bonus points for the grade of that TP.
Posted by Gianluca Rizzo at 13:33
TP3 Report Submission
Next week I will not be in Lausanne therefore cannot hand-in the TP3 report on paper, can I submit it via email instead? If so, to whom should I send it to? Thank you.
Posted by Roberto Cardona at 10:35
TP3 - Problem 1 - recommendation
Hi all,
in Problem 1, we recommend you to assign to all network interfaces which are on the same hub Ip addresses on the same subnet.
Also, on page 18, for the question "How many paths exist....", you should answer according to what you observe at router R1.
Posted by Gianluca Rizzo at 17:19
Tp3, redistribute...
Hi,

We have a little hesitation. If we understood correctly, the command "redistribute connected" will only tell the neighboring bgp routers about the on-link subnets of a given router. i.e. R4 will only tell R2 about the subnet going towards R6 but not anything it learned from R6. (It is at least what we seamed to experiment). Is this correct?

If so, how can we make routers forward information they received avoiding the use of the "network" command which would require a router to know exactly in advance what he will be advertised?


Thanks for your help,

Group A19.
Posted by Christophe Gudin at 17:13
Comments (1)
TP3 - precisation
Hi all,
in the pictures for problem 1 (p. 15) and 2 (on p.20), when you have to configure a BGP speaker, and you have to decide with which BGP speaker of a neighboring AS it has to estabilish a TCP connection for BGP data exchange, you must choose the one which is geographically closer (according to the picture) to the one you are configuring.
As an example, as the figure on p.15 suggests, router R5 will choose as neighbor router R3 of as 65341, and not router R4.
Posted by Gianluca Rizzo at 17:44
TP3 - advice - save your config files
Hi,
we advise you to bring to the lab a floppy, or an usb key, in order to save your config files for the next time you come to the lab.
Otherwise, you could connect the machines in the lab to the internet (see TP1), and move your files to any machine to which you have access.
Posted by Gianluca Rizzo at 17:51
Comments (1)
TP3 - errata corrige
Hi all,
some corrections on the text of TP3:

-on page 5: in the script, the line that launches zebra should have the syntax:

zebra --user root --group root -d -f zebra.conf

-in order to use the command "show running-config" via telnet, you have to pass to privileged mode (that is, type "ena" on the telnet command line);

-on pages 9-10: for the command access-list, the prefix should be in the form (ip_address netmask).

-for the exercise on page 12-13, on question 2: in the case in which the TCP connection between AS 65099 and AS65101 goes down, we admit that the router in AS 65101, receiving two advertisements for network x.y.z.a/w with the same AS path length, it will choose the one passing through AS 65102.

Thanks
Posted by Gianluca Rizzo at 17:47
Comments (1)
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