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Problem Set 1 Discussion (Q/A)

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Problem Set 1



Kaushik wrote: Could somebody send me (kaushikb@cc) the converted ASCII files (after using MRTD) for problem 4 ?? I am having problem installing mrtd on salo..
Kaushik wrote: Problem 1, part 4d (ii) – Do we have to do traceroute from GT to k.root-servers.net OR from k.root-servers.net to GT ?? The question seems a bit misleading

Has anyone tried to run the ruby scripts on COC machines? I tried to run it on Myrna since Helsinki is down. However, i encountered the following error message even without any modification to the code:"
./resolv-pset.rb:1811: unmatched (: / (RegexpError)
(?:#) |
(?:#) |
(?:#) |
(?:#)/
from ./StubResolverIter.rb:3:in `require'
from ./StubResolverIter.rb:3
from ./resolve.rb:9:in `require'
from ./resolve.rb:9
"
May i know what should be the right procedure to execute the script? (I have copied the optparse.rb from my windows installed lib directory to the linux server, since i can't find the optparse.rb either in the package or in the server.)

Answer to myself: i just found out that the Ruby code runs on Salo and Helsinki, but not on Myrna.

Question 3:
How can I locate georgia tech in the bgp routing file.

Question 2:
Ask to use seven of eleven IS-IS packet traces. Only one of the trace address is given, how can I, and where can I find the rest. Please answer here with the links. _

Kaushik wrote:
How to observe the BGP table dumps from Abilene Network (Problem 4) ... I tried opening in Wireshark and vi but it didn't work..

Guillaume wrote:
Same problem here...

Min Yang wrote: i think it needs MRTd to convert the file, as stated in http://www.abilene.iu.edu/abilene/research-data.html. However, i tried all the possible websites to try to download it, unfortunately, all the websites are not accessible. The downloaed perl script could not even be decompressed! :-(

Sriram wrote:
The mrt program converts the unzipped file to ASCII format. I got it from http://ftp.debian.org/debian/pool/main/m/mrt/mrt_2.2.2a.orig.tar.gz .
I am unable to understand what the question 4.1.(d) is asking. What does which prefixes are reachable mean? Doesn't an entry mean that?
Min Yang wrote:
Problem 4, sub-question 1, part b: i tried to find out all the corresponding corporation to each AS, which has eBGP session with Abilene, (i.e. eBGP column value = 1), it seems that Microsoft is not inside. I also dig out about 11 AS numbers belonging to Microsoft, including one from research, however, none of them is inside the session table. How many ASes does Microsoft have?

Kaushik wrote: Yes, Microsoft ASN is not there..it ranges from AS 8068-8075

Junjie wrote: I found some other ASN for Microsoft in http://www.arin.net/whois/, but it seems that Microsoft asn is still not in the table.

Nitya wrote: likewise

Kaushik wrote:
Does anybody know how to import the mysql tables in problem 4 ??

Min Yang wrote: Just figure out. Actually, it is simple. Assume it is running on windows.
1. Create 3 different tables config_if, config_isis and config_ospf in your mysql server
2. Copy all those unzipped files in the config_if, config_isis and config_ospf directories into the corresponding directories under c:\programe files\mysql\mysql server 5.0\data folder.

Then, when you can execute your normal sql queries.

Sriram wrote: The files do not load properly when I used them with MYSQL 4.1.11 on Fedora Core 4. Although i was able to see the databases of config_if.. when i tried to see the tables, the fields were reported to be empty in all tables except for the as_regexps,bogon_list . Although I don't know the exact reason for the problem, I suspect an incompatibility with MYSQL 4.1. When I installed MYSQL 5.0.33 everything works fine.

How can we do it in Oracle running on ubuntu/linux. Where to put these files/folders.
Guillaume wrote : install mysql (sudo apt-get install mysql) then follow instruction for Windows (except that files are located at /var/lib/mysql/)
Question 2:
What is meant all LSA. do we have to calculate the propagation delay for all the LSA's in the trace. How do we know the originator of the LSA to trace the lsa through the network.How can we make 7x7 matrix with one trace. It would just be one row. Here, again I need to know who is the initiator. Can anybody help.


In Problem 2 I find that some of the propogations delay are negative , probably because of clock synchronization issues. Did anyone else face this issue?

Min Yang wrote: i think you have to check the clock time in the frame header rather than using the relative time in the LSP packet header. I did in this way, and found the result to be reasonable.

Junjie wrote: yes, I found some delays are negative, caused by "21:11:26.216749 IS-IS, L2 LSP, lsp-id 0000.0000.0017.00-00, seq 0x000263e8, lifetime 1189s, length 463" in HSTN. It is weird that the lifetime here is 1189s, others are 1198s. And I use the time stamp like "21:11:26.216749" to compute the delay. So why?
Min Yang wrote:
1. For prob 3, sub question 3, part b, i could not get the meaning of the question "What is the maximum number
of routing table entries that this single CIDR address saves? Why is it that we can only
infer the maximum, and not the actual, number of addresses that this CIDR address
saves?" R u trying to ask something relating to aggregation?

2. For prob 3, sub question 4,
What is the difference between part b and part c? Since part b means the best route, what is part c referring to?
Kaushik wrote:
For prob 2, how do you observe the .gz files after downloading them ?

A: Use Wireshark or Tshark

Nitya wrote:

I am having trouble untaring the files (abilene-rcc.tar, abilene-pset.tar) for the fourth problem. If anyone has been able to do this, could you please tell me how.

A. Use this command
tar xvfz abilene-rcc.tgz
tar xvfz abilene-pset.tgz
Or use a program like 7-Zip
Min Yang wrote:
Another question on problem 2:
1. When we create the CDF, can we just ignore the 0s, i.e, the diagonal value in the 7x7 matrix?

Min Yang wrote:
Three questions on Problem 2: Understanding IS-IS
1. Regarding sub-question 2, the refresh interval is referring to the LSP aging time or the hello interval?

A. Since LSPs are flooded, you should be able to track the propagation of an LSA across the network

2. What is sub-question 3 trying ot ask?

A. oooops! There's no question there. Freebie. :)

3. Is the link state announcement referring to LSP (Link state packet)?

A. Yes.

Kaushik wrote:
By observing a path, say A B i, in the table dump, how can we determine the peering relationship (Peer/Customer/provider) between A and B ??
Kaushik wrote:
In problem 4, part 1(f), I haven't understood the meaning of 'collection setup' and 'measurement box'. Could somebody please throw some light on this ??

Guillaume wrote:
Nick answered sometehing like : The question here is basically "why are the next-hop IP addresses in this
table from many different networks...?"
Nitya wrote:

Q: In Problem 2, From the packet trace for the Atlanta observatory I find two hostnames ATLA-m5 and ATLAng-re0. Are these two different hosts or the same? Also to find out the average end - to - end delay of LSA between router pairs, we need to see the LSA going out of a router & and coming into another. With packet traces from 7 routers, I think that I will be able to obtain only a 7x7 mtrix. Am I missing out on something?

Those are two different hosts.

Yes, that should read 7x7.

Kaushik wrote:

Q: In Problem 1, subquestion 1(d), when we run the command to obtain the mail servers for cc.gatech.edu, it returns 5 mail servers. How do we distinguish the primary mail servers and the secondary mail servers from these (All of them have the same priority/preference) ??

A: That is the point of the question. :) A good place to look would be the DNS RFC.
Sriram wrote:

Q: In question 4 of part 2, the expected propagation time of an LSA is asked. IS one supposed to use the distances between the routers and calculate the propagation time for the 7 x 11 matrix for different paths between 2 routers and average it? I am also assuming that propagation time is strictly the time to transmit a bit and does not include others like transmission and queuing delays.

A:
  • You should be able to get the propagation times from the packet dumps (i.e., you'll see the LSA packet get sent from one router and received at the other).
  • Each element in the 7 x 11 matrix should be an average propagation time.
  • Your last assumption shouldn't apply; you can get the times directly out of the packet traces.
Min Yang wrote:
  • Question 1, How to perform traceroute from k.root-servers.net? It seems there is no such website of http://k.root-servers.net. The only available website of http://k.root-servers.org seems not have the traceroute interface. Or r u referring to get look glass server in RIPE or LINX to do the traceroute?
    • A: Yiiiiikes. Use http://www.traceroute.org/ to do this. If the problem set omitted that, sorry for the confusion.
  • Question 2, what is CDF?
    • A: Cumulative Distribution Function. I'll explain in class tomorrow.
  • Question 4,
    • which file is the BGP table dump? Those files in the RIB directory or Update directory?
      • A:RIB directory.
    • Do we need to use all the files on 22nd Jan from all the routers?
      • A:In problem 3, you're using the routeviews table dump (read the first paragraph; let me know if that's unclear). There's only one of those, and I've given you the link to the table you should use. :)

How can I download the dns-resolv-rb.tgz
I tried to download it many a times, but this file always downloaded with size 0.

Can anybody send me good and easy read article that explains dig. I dont even understand the question asked in the assignment.
My query dig cname cc.gatech.edu returns no answers. Are you getting any results with this query. Question 1 part c

Try www.cc.gatech.edu
The CNAMES are there to distinguish different services running on the same server.
Try ftp.cc.gatech.edu as well as things would become more clear