FAQ - CSCI 558L, Fall 2009

Q:		I got the key, but I couldn't open the door, is there combination code?
A:		No, there is no combination code. You might want to try the lower keyhole.
Q:		What is time slot for lab exercises?
A:		Because we have limited number of routers, each student is assigned several time slots each week for doing lab exercises. During your assigned time slots, you have exclusive use of the assigned routers. Each time slot is four-hour long. There are two sets of routers, called Rack I and Rack II. So, each week has 2 (racks) * 7 (days) * 6 (slots/day) = 84 time slots.
Q:		What are the passwords of Linux machines and routers?
A:		The password of Linux machines is on the lab whiteboard. Routers don't have passwords. Do not change any password. In case when you configure routers and are asked to "Enter router password:" or "Enter router secret:", just do <Ctrl+C> to abort the configuration dialogue. You will come to command line prompt. You are supposed to configure the router at command line.
Q:		How will our submissions be graded?
A:		Most points are given to the trace files and the reports. The trace files can show whether you did the exercises correctly. Some questions ask you about the phenomena of the exercises, you should explain why they happen, not just answer yes or no. You can also write your thoughts or comments about the exercises in the end of the report to help us improve them.

Q:		I can't get minicom to work, how should I set the parameters?
A:		/dev/ttyS0, 9600 baud rate, 8N1, No flow control.
Q:		Can I download router's configuration file to PC?
A:		Yes, you can use tftp to download and upload router's running-config. Read the man pages and Cisco documentation to figure out how to do it.
Q:		I can't find tftp server and client in Linux machines?
A:		The tftp server and client may not be installed in Linux. Get the Linux CDs and install tftp-*.rpm. The server should be called in.tftpd and the client tftp.
Q:		Do I need to clean up the configuration information on the routers and the Linux machines? Can you tell me what should I do?
A:		Yes, you should clean up all your configuration of both the Cisco routers and the Linux machines. To erase the configuration on Zebra, you may delete the configuration files (zebra.conf, ospfd.conf, bgpd.conf) under <where-you-install-zebra>/etc. To erase the configuration on Cisco routers, do a "clean startup-config".
Q:		I've set the IP address on the corresponding interfaces, but routers can't ping each other. Do you have any suggestion?
A:		I assume you've made the correct IP address assignment. First, you should make sure the the cable connection is Ok. Second, the Ethernet interface on the router shall be UP (you should figure out the Cisco command to bring up the interface). If the problem is still not resolved, send email to TA.
Q:		How do I configure F such that it belongs to different AS?
A:		Multiple instances on bgpd.
Q:		I think the Ethernet card on F is not working, I couldn't access to the Internet even if I set the IP address, gateway and DNS correctly.
A:		There are 2 Ethernet cards on F, the upper one (eth1) is supposed to connect to the external LAN. The problem is due to the fact that you configure eth1 but plug the cable to the lower NIC (eth0).
Q:		I'm trying to configure A, C and F into one subnet...
A:		You don't need to do that. All nodes in a subnet must be able to communicate with each other directly (e.g. they are all connected to the same Ethernet segment).
Q:		Do I need to configure virtual interface on C, D, E?
A:		If you want to keep Internet access on these machines, you should.
Q:		Router A and B do not exchange BGP info, why?
A:		This is a common problem that happened to many students, it is very likely that something is wrong in the configuration of Router A and B. You might want to do "no synchronization" in A and B. And setting the cluster-id may help. Here is a pointer to the Cisco page on troubleshooting when BGP routes are not advertised.
Q:		I have problem in setting up multiple instances on F, do I need to use view?
A:		Yes. The current Zebra implementation seems not supporting BGP multiple instance perfectly. But If you manage to set it without using view, please let me know...
Q:		How do I know whether the route reflector is working or not?
A:		One good way to debug the configuration is to collect traces on the routers. On zebra machines, you need to enable debug to collect the trace (the zebra manual doesn't say this). By analyzing the trace, you will get many hints on what happened and what might go wrong.
Q:		Can you explain why we need "no synchronization"?
A:		When synchronization is enabled, the route reflector will not advertise the routes it learns from its clients to other BGP peers (outside that cluster) if the route can't be validated in IGP. We need to do this since F is not running OSPF and the route advertised by F is usually non-existent.
Q:		What is the difference between routing table and BGP routing table?
A:		Routing tables store the routes that routers use to forward packets. BGP routing tables store only the BGP routes that are dynamically learned from neighbors or statically configured. Similarly, OSPF routing tables store only the OSPF routes. Routers will merge static routes, OSPF routes, and BGP routes into the routing tables.
Q:		How to get the trace and BGP routing messages on zebra?
A:		Put the following commands in bgpd.conf: debug bgp updates log file bgp.trace dump bgp all bgp.packets The trace file (bgp.trace) is in text format, while the dump file (bgp.packets) is in binary format which is called MRT format. There is a tool (route_btoa) in the MRTd package (http://mrt.sourceforge.net/) that can view the dump file. A copy of the executable is available here. This tool will generate output like: % ./route_btoa bgp.packets TIME: 1092084092 [08/09/04 13:41:32] TYPE: BGP4MP/MESSAGE/Update FROM: 198.32.16.49 AS4 TO: 198.32.16.54 AS65530 ORIGIN: IGP ASPATH: 4 NEXT_HOP: 198.32.16.49 MULTI_EXIT_DISC: 0 ANNOUNCE 192.228.79.0/24 You should submit the original binary dump files. Do not convert it to text format.

Some suggestions:

1. Make sure you have a clean system, reinstall the system if you think it is necessary;
2. Make sure the network connection is working, also you should check it from time to time;
3. If C, D, and E complain that they can't find the route to the network that F advertises, try adding a static route on C, D, and E, telling them that it can be reached through F.

Q:		There are no enough transceivers in the lab. How can we setup the topology?
A:		Instead of connecting two machines via a direct link, you can connect multiple machines via the hub. The physical topology may not resemble to the one shown in the exercise, but the logical topology should be the same. Hint: make sure the target and the sinkhole use dedicated links, so when you run tcpdump on these machines, it won't capture the traffic not belonging to them.
Q:		Do we have to put all machines and routers in the same AS?
A:		Yes.
Q:		When I trigger the blackhole or sinkhole routes, they don't propagate to other routers. Why?
A:		Remember that BGP requires the I-BGP peerings in full mesh. You can setup a full mesh peering topology, or use route reflection you learned in exercise 1. Depending on your configuration, you may also need to run OSPF.
Q:		Do we need to run zebra in machines?
A:		No, you can configure static routes in machines so that they know how to reach each other.

Q:		What you mean by sending back-to-back UDP packets?
A:		It means you should send UDP packets as fast as possible.
Q:		How can I know the TOS octets of packets are set correctly?
A:		You can use tcpdump to check the trace files. If packets have the tos octet set, tcpdump will show something like [tos 0xAB] where AB is the value of tos octet. Remember that precedence field is the first 3-bit of tos octet.
Q:		My submission tarball is huge, how can I submit it?
A:		You can use lab machines or public email account (e.g. Yahoo, Gmail) to email them. If you use lab machines, remember to set the email's "Reply-To" to your regular email address where the confirmation mail will be sent.