RS interview report 2.3

卡农ccc

1、STP、RSTP
2. Campus network gateway
3. What will switches and routers do when they receive data without table entries

Answer order: 1, 3, 2.
1. From the port role, we can start with: role, status, BPDU (type, flag, sending mode, aging time, processing of secondary BPDU), topology change, fast convergence, and four kinds of protection
PS: after speaking for more than 20 minutes, I didn‘t interrupt in the whole process. I felt strange, and then I offered to finish
Question: where is BPDU protection configured? Orders? ---------Global, STP BPDU protection default ; Examiner: default? Sorry, wrong, enable
Question: where is root protection configured? Orders? -------------DP port, STP root protection, generally configured on the access layer
Question: Why are so many specified ports in the access layer? Can‘t you go up the root bridge? ---I didn‘t answer. I confessed to the examiner
Question: why is loop protection configured on RP and AP? ----Here the train of thought is confused, did not answer, the examiner also said behind what did not hear clearly

2. Unknown table entry
Answer: the switch receives the unicast frame and checks the MAC address table according to the destination MAC. If there is no table entry, the ports in the VLAN other than the receiving port will flood
When a router receives a packet, it looks up the routing table according to the destination IP, forwards it if there is one, and discards it if there is none"
Then, I will talk about how to deal with unicast, multicast and broadcast received by the switch (only BPDU is mentioned in multicast frame, IGMP snooping is not mentioned)
How to deal with unicast, multicast and broadcast received by router

After talking about it, I found that it was only 7.8 minutes. I felt that I couldn‘t give it a chance. So I talked about how to deal with the unicast, multicast and broadcast received by the layer 3 switch. There was still a long time left. So I mentioned how to judge the unicast and multicast frames. I found that there was still a long time left, so I took the initiative to tell the examiner that I had finished (I was stupid, I could just say something else)
Question: let me draw a picture of how two exchanges and two PCs connect to each other in the same network segment, and tell you the detailed process?,
A: first, in the same network segment, send ARP request, write out the target IP, MAC, sender IP and MAC in ARP, then go to port 1 of SW1, type PVID (here the examiner does not draw VLAN, I will follow the default processing), then strip tag from port 2, go to SW2... Finally, PC2 sends ARP After receiving, PC1 adds IP-MAC mapping to ARP table, and then encapsulates ICMP, IP and MAC


Question: how to deal with the data frame of SW1 when the interconnection interface between switches is configured with trunk?
Answer: all switches have tags inside. When sending out, check whether they are in the allowed list. If so, check whether they are the same as PVID. If they are the same, separate them and send them directly
How to deal with the receipt of SW2?
A: I talked about how to deal with those received with tags and those not (the follow-up questions are relatively simple)


Question: suppose there is a layer-3 switch and there is no gateway on the PC, how can I access it?
Answer: if the PC is not equipped with a gateway, it will not generate a default route to the gateway. You can turn on the ARP proxy. When the switch receives the ARP request and finds that the destination IP is not the IP address of its own vlaif interface, it will respond to the MAC address of its own vlaif interface to PC1, and then the switch will forward it instead


Question: do you reply directly? Is there anything you don‘t need to do?
Answer: if you have an ARP entry of PC2 in your own ARP entry, you will return it
Do you know the ARP Miss message?
A: when an attacker appears


Question: must it be an attack?
A: not necessarily... Then, if the device receives an IP message that cannot be resolved by the destination IP, it will generate an ARP Miss message. The destination IP cannot resolve the route corresponding to the destination IP, but there is no ARP entry corresponding to the next hop in the routing table

3. Gateway
First, cost, second, resources, third, scalability, fourth, gateway redundancy, fifth, forwarding efficiency, sixth, routine maintenance, seventh, isolated broadcasting, eighth, fault location, ninth, control level, tenth, line efficiency


There is still no interruption in the whole process. I don‘t know what to say after I finish speaking, and I take the initiative to tell the examiner that I have finished speaking
Question: where is the gateway redundancy? Why is the stack used in layer 2? Do you know m-lag?
A: sorry, it‘s not very clear.

Q: you mentioned load in VRRP. Now there are two different businesses. How do you implement it?
A: three switches are drawn with inverted triangle. The switch SW1 below connects two PCs. in the same gateway 1.1.1.1 and 1.1.1.2, there are different gateways 1.1.1.253 and 1.1.1.254 respectively. PC1 is in vlan10 and PC2 is in vlan20. Then MSTP, vlan10 --- endurance 1 and vlan20 --- endurance are deployed in the three switches 2. SW2 and SW3 are the root bridge and backup root bridge of instance 1 and 2 respectively. Meanwhile, SW2 and SW3 create two vlanif10 and vlanif20 respectively, and deploy VRRP. SW2 and SW3 are master and backup respectively


How do they get their traffic?
Examiner: don‘t elaborate, just tell me how to get there
Answer: you must find the gateway first, and the traffic will go to SW1 first... Then ask the examiner whether they are in the same network segment?
Examiner: you planned it yourself, and you asked me, don‘t you think there is something wrong with the planning?
Answer: Yes, I changed the address of PC2 to 2.2.2.2, and then the traffic got stuck in SW1. So the examiner asked, what is the tree of your instance 1 and where is it blocked? When I say XXX blocking, what is instance 2 like? Where is the blocking? I said that XXX is blocked, and the flow goes from XXX. Examiner: right, that‘s how it comes down (pc1-sw1-sw2-sw3-sw1-pc2)

Final comments
Chief examiner: finally, I know under the guidance here. Is there anything the Deputy examiner wants to say
Associate Examiner: you have talked a lot about theories, such as root protection and loop protection. Why should they be equipped there? Go down and think more about why, and then let me finish the exam.

There are still some questions that I forget what it is. I feel it‘s relatively simple as a whole. Unfortunately, I didn‘t answer a few simple questions. The examiner is very kind. I hope the students behind can ask questions. Come on!
  
            

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