The Tencent Interview (one side)

Suddenly called me at about 4:30 in the afternoon to talk to me about the interview. I remember I had voted for more than a month, but I was flattered by the news...so that I don’t remember any job group I voted for...

To get back to the subject, I started by introducing myself, introduced the school, what I learned, and the position I wanted to work in (I forgot all of them). Then began the technical interview.

1. What did you do in school and what projects did you have?
   Answer: I'm talking about the experiment of IGP's comprehensive networking, redistributing routing filtering between multiple routing protocols, realizing network interconnection, talking about the division of labor of the project, and then the process of project implementation.

2. What is the difference between OSPF and BGP?
   Answer: I don't think it is good or bad, because the difference is too big. I don't know where to start. First of all, I said one is the external gateway routing protocol, the other is the internal gateway routing protocol; OSPF is a link state routing protocol, BGP is an enhanced path vector routing protocol; then the underlying implementation is different, BGP is based on TCP, OSPF It is based on IP. BGP uses the autonomous system as a hop, OSPF is not; then BGP establishes neighbors on physical links that can not be directly connected, but OSPF is not; their neighbor discovery process is also different, I replied that this is different There are too many points... Now that I think about it, I can talk about the characteristics of BGP, routing rules, some rules of BGP routing distribution, alas.

3. The process of OSPF neighbor establishment
   A: I still answered this very well. I have explained the whole establishment process completely. I will not go into details for details. There are too many.

4. The role of arp
   A: I said that ARP is an address resolution protocol, which resolves the MAC address from a known IP address (and did not answer too much).

5. How to express an IPv6 address in the IPv6 address space?
   Answer: I only know that it is 128 bits.

6. QoS
   Answer: The service quality level, I didn't learn the finer... I made up for the evil, and sent all kinds of data through different levels. I didn't answer the specific implementation.

7. I asked about the implementation of the network failure project written on my resume.
   A: This is the content on the resume, which depends on personal circumstances.

8. Specific implementation measures for load balancing
   A: I just talked about the Ethernet link bundling, and then LVS can achieve server load balancing. I didn't quite understand the specifics, and only talked about some concepts.

9. What is the situation of ***** in traceroute? ? ?
   Answer: I don't know. After follow-up query, it seems that the firewall blocked the ICMP return information, so we can't get any related data packet return data.

   The query knows: The source sends an ICMP Equest, the TTL of the first request is 1, and the TTL of the second request is 2, and then increments to the 30th.
   The router in the middle sends back ICMP TTL-expired (ICMP type 11) notification source, (packet is dropped due to TTL timeout at the same time), so the source knows every router passed along the way; the last destination is sent back to ICMP Echo Reply (the last hop will not return to ICMP TTL-expired).

   So if ICMP Echo Request is sealed on any router in the middle, traceroute will not work; if type 11 (TTL-expired) is sealed, the router in the middle cannot be seen at all (it is ***), but the packet arrives. The last destination; if the ICMP Echo Reply is sealed, the omnipotent in the middle can see it, but the last destination cannot be seen.

   If you use traceroute on Linux, the udp protocol is used by default, except for the first hop, the rest are * * *. 80% is because the virtual machine nat router discards packets with port>32767 by default. So everything is explained. Completed.

10. Network communication quintuple
    Answer: Source port, source address, protocol number, destination port, destination address.

11. Python's data structure, the difference between tuples and lists.
    Answer: I didn't play well and I was a little nervous. I also forgot to say...

Big companies are big companies, and they don't know many details. Let's not talk about it, study it, alas.