Basic Multicast part 1 – PIM Dense Mode
March 16, 2012Laurent PratLeave a commentGo to comments
I would like to share some basic Multicast examples. As this topic is quite wide I will make different posts. This first post will talk about PIM Dense Mode. The next post will cover topics such as PIM Sparse Mode, Auto-RP and PIM BSR.
Let′s consider the following topology:
Source: The multicast source 150.1.0.4 will be sending to multicast group 239.10.10.10 which is part of the administratively scoped addresses assigned by IANA which is for use in private multicast domains, much like the IP unicast range defined in RFC 1918.
IGP: The IGP used is EIGRP
Platform/IOS: Cisco 2691/12.4(15)T11Adv IP services
Let ′s start with Dense Mode. PIM Dense Mode is based on the “push” or “implicit join” model where Multicast traffic is flooded throughout the entire multicast domain without the receivers needing to join the specific multicast group being flooded. So PIM Dense Mode is not really scalable and is only suitable for small multicast implementations. The reason of that is the flooding and the (S,G) state creation for every source/group.
Let′s enable IP multicast routing PIM Dense Mode on all the routers. As soon as we enable PIM on an interface the router starts to send multicast PIM hello packet to 224.0.0.13 in order to form adjacency with the others PIM neighbors. This information will be used by PIM to know where to forward multicast packets. PIM packets are encapsulated inside IP packets with protocol number 103.
Now that PIM dense mode is enabled on all the routers let′s send multicast traffic from the source 150.1.0.4 to 239.10.10.10. Please note that the receiver hasn′t joined the group 239.10.10.10 yet.
If we do some debug ipmpacket (disable mroute-cache on the interface in order to see the debug output) on R3 just when the source starts sending multicast traffic we can see the following output:
We can see that R3 is forwarding multicast traffic received on its RPF interface both out its interface f0/0 connected to 200.1.0.0/34 network and out its serial interface connected to the Frame-Relay network. Actually these interfaces are used to forward multicast traffic because R3 has a PIM neighbor on each of these interfaces. Interface F0/1 is not used for forwarding multicast traffic because this interface is the incoming interface for incoming multicast traffic. It is the incoming interface because it has passed the RPF check that is to say when R3 receives the first multicast packet from the source; R3 uses the unicast routing table to perform the RPF checks and look at the source IP address (150.1.0.4) and because this interface is used to route packet out to 150.1.0.4 it is elected as the RPF interface. The RPF interface is computed as the interface with the lowest cost path (based on AD/metric) to IP address of the source or in case of Sparce Mode (*,G) the RP. If multiple interfaces have the same cost, the interface with the highest IP is chosen as the tiebreaker. The RPF check is run every 5 seconds and the outgoing interface list is adjusted appropriately so the RPF interface never appears in the outgoing interface list.
A show iprpf demonstrates that F0/1 is the RPF interface for this source:
The ?means that the DNS lookup has failed for 150.1.0.4.
Now let′s look at the multicast routing table on R3:
From the above output we can tell that R3 is running in Dense Mode for the multicast group 239.10.10.10. The D flag in the (*,G) entry tells us that. Actually Dense Mode uses only (S,G) entry to forward multicast traffic so you may wonder why is (*,G) also present in the multicast routing table. Well that is because Cisco′s implementation automatically creates a parent (*,G) state whenever (S,G) state is created. So whenever it is necessary to create a (S,G) entry a corresponding parent (*,G) entry is automatically created first.
The outgoing interface list (OIL) of an (*,G) entry reflects the interface where other PIM-DM neighbors are connected or directly member of the group exist. In this case R3 has PIM neighbors on F0/0, F0/1 and S0/0.1 which are respectively R4,R5 and R2. Furthermore the OIL of the (S,G) child is populated from its parent entry (*,G), that is why S0/0.1 and F0/0 are present in the OIL of (150.1.0.4,239.10.10.10). Please note that F0/1 is not appearing in the OIL of the (S,G) because it is the RPF interface and that would defeat the purpose of multicast loop prevention mechanism.
The T flag on the (S,G) entry means that traffic is forward via the SPT which is the shortest path to the source based on the unicast routing table. Also the RPF neighbor is 0.0.0.0 because the source is directly connected to R3.
Please also note that both interface are in forwarding mode and the expire timer will never expire for these interfaces as long as the source is sending packet. Every time the router sees a multicast packet it reset the timer for the (S,G) entry. When the source stops sending multicast traffic the timer for the entry will expire and the (S,G) entry will be deleted which will in turn trigger the count down timer to start for the (*,G ) entry and after 3 minutes this entry will also be deleted.
If we look closely at a debug ippim/debug ip packet on R3 when the source has just started to send multicast traffic we can see the following:
If you take a look at the diagram you would see that R5 and R3 are both connected to the network 200.1.0.0/24. What is happening is when R5 receive the first multicast packet from the source it will trigger the RFP process to determine if the packet arrived on the correct interface which it does as the source is directly connected to both R5 and R3. So based on the succeed of the RPF check, R5 now forwards the multicast packet out F0/0 which is present in the (S,G) OIL built from the parent entry (*,G) [see above explanation for details]. So now you can guess what is happening. There will be duplicate multicast traffic on the 200.1.0.0/24 network because both R3 and R5 are sending multicast traffic out F0/0 so there will see each other multicast packet coming in their multicast outgoing interface. To avoid this kind of situation PIM has a feature called PIM Asserts which basically triggers a PIM router to send a PIM assert message to all PIM routers (224.0.0.13) containing the source IP, the group and the path cost (AD/metric) to the source every time it receives a multicast packet on its multicast forwarding interface.
In our example because R5 receives a multicast packet on its multicast forwarding interface F0/0 it sends a PIM assert packet to R3. When R3 receives the PIM assert packet (see output above) it compares the metric announced by R5 to reach the source 150.1.0.4 to its own metric and because the metric are equal (both R3 and R5 are connected to the same network where the source is connected) the highest IP address is used a tiebreaker. In this case R5 has an higher IP (200.1.0.5) than R3 so it wins the right to forward traffic on this segment while R3 must prune its interface (F0/0) connected to 200.1.0.0/24 .
As a result of losing the assert process R3 sends a PIM prune packet for (150.1.0.4,239.10.10.10) to R5 (see output above). But what will happen to R4? It still needs (if there any receiver downstream that may be interested in receiving this multicast flow) to receive multicast traffic in order to forward it down to the Frame-Relay network. Well PIM uses a process called Prune override to overcome the situation where R5 will prune its interface connected to 200.1.0.0/24 network as a result of receiving the PIM prune packet from R3. Here is how it works.
When R3 sends the PIM prune packet to R5 as a result of losing the assert process R4 will also hear this message as it is multicasted to all PIM multicast enabled router (224.0.0.13) and because the OIL of R4 for (150.1.0.4,239.10.10.10) is not NULL (R4 hasn′t received a prune message on its multicast forwarding interface (S0/0.1)) and it has a PIM connected neighbor, R4 sends a PIM join (150.1.0.4,239.10.10.10) to R5 in order to override the previous prune from R3.
To make pruning works a 3 seconds delay timer is started when R5 and R4 receives the prune message from R3 which means that R5 will wait 3 seconds before pruning its interface F0/0. As it receives a PIM join from R4 within this interval the interface is not pruned and the multicast traffic can continue to flow normally.
Now that multicast traffic is being flooded let′s have a look at the multicast routing table of R1 which is a leaf of the multicast tree:
So there is an issue there. R1 has no entry in its multicast table for the multicast group 239.10.10.10 although the source is sending multicast traffic to this group. Let′s have a look at R2 which is the hub of the Frame-Relay network:
So R2 is saying that it has an entry for this group but the entry is pruned which is one of the reason why R1 is not receiving this multicast flow. But there is another issue here. From the output above R2 is saying that the RPF interface (incoming multicast interface) is S0/0 which
is correct as R2 has only one interface. Next R2 says that its RFP neighbor is R3 which is based on the best path metric to reach 150.1.0.4:
So R2 is choosing to route through R3 due the lower cumulative delay.
But let′s come back to the previous output. What is happening is that as we saw before the incoming multicast interface or RPF interface cannot be present in the OIL and that is what we can see in the output. As the incoming interface is s0/0 this interface cannot be present in the OIL of (150.1.0.4,239.10.10.10) which means that the OIL of R2 for this group is NULL which in turns triggers PIM to send a PIM prune for this group toward the RPF neighbor of R2 that is to say R3 which is confirmed by the following output:
So R3 Prune the interface S0/0.1 in its OIL for (150.1.0.4,239.10.10.10) during 3 minutes.
Then the flooding of multicast will start again out this interface and R2 will send a PIM prune again and the process goes on and on. That is the flooding/pruning behavior of PIM Dense Mode.
So to conclude R1 is not getting the multicast traffic because R2 is unable to forward multicast traffic back to the same interface it was received on and this is due to the RPF check process that says that an RPF interface of a multicast forwarding entry must never appear in its outgoing interface list. The second issue is that PIM treats the Frame-Relay interface as a “broadcast” media that is to say it assumes that all the multicast packets received on this interface are heard by all members connected to the Frame-Relay network which is not the case in reality unless the Frame-Relay network was fully meshed. So when R3 forwards a multicast packet only R2 received it on the Frame-Relay network as R2 will never forward the packet back out the same interface. There are 2 solutions to solve this issue in Dense Mode: ?Configure point-point sub interfaces on the hub R2
?Use Multicast tunneling
If we were using Sparse Mode there will be a third solution which will be to use PIM NBMA mode which is an extension of the PIM protocol for WAN interfaces. In our case we cannot use this method as PIM Dense Mode is based on the “implicit join” model and hence PIM NBMA will not be able to track the different PIM join messages.
In this example let′s configure a tunnel between R2 and R1 to solve the Frame-Relay issue so we can send multicast traffic from the source all the way down to R1.
So once the tunnel is configured between R1 and R2 let′s try to send traffic again from the source. If you look at a debug ipmpacket on R1 we now get the following:
R1 can receive the multicast traffic from R2 via the tunnel interface. The issue now is that when R1 receives the first multicast packet via the tunnel interface it does a RPF check on the source IP address using its routing table and find out that the RPF interface for 150.1.0.4 should be via S0/0.1 and not the tunnel interface. This is because R1 has learned the 150.1.0.0/24 via EIGRP and not via the tunnel interface. So the unicast shortest path does not match the multicast distribution tree. To solve this issue we have to use a static mroute statement to allow R1 to perform the check correctly:
This command does not specify any forwarding rules. Instead, it creates an ordered table entries to look up for RPF information. Note that the mroute table is ordered in the same way you enter the IP mroute commands so you should enter the most specific mroutes first.
When a router finds RPF information in both the unicast routing table and the mroute table it prefers the mroute information since the AD is better (AD=0). In this case the AD for the unicast routing table is 90 (EIGRP).
Let′s try to send multicast traffic from the source again and see what happens now that we have solved the RPF issue. Let′s have a look at the multicast table of R1 while the source is sending traffic:
So now R1 has the correct entries for the source 150.1.0.4 in its multicast table. But there is still one issue :-) If you look closely at the OIL for the (S,G) R1 says that it will forward multicast traffic out its Frame-Relay interface (not the tunnel which is the RPF interface) which will actually cause a loop in the network because upon receiving the multicast packet from R1, R2 will make an RPF check and that will succeed because the multipoint Frame-Relay interface is the RPF interface. While the source sends traffic we can actually see the loop between R1 and R2 with a debug ipmpacket:
The following diagram illustrates this multicast loop process:
So to solve this issue there are 2 solutions:
?Disable PIM on the Frame-Relay interface of R1 so only the tunnel interface will be used for multicast data plane and control plane traffic
?Configure point-point sub interfaces on the hub R2
In this this example we will just disable PIM on the Frame-Relay interface of R1. So now let′s have a look at the multicast table of R1 when the source is sending multicast traffic:
So now things look correct. As a result of the OIL being NULL R1 sends a PIM prune to R2 as it doesn′t need to receive multicast traffic because it hasn′t any directly connected members or PIM DM neighbors on this interface. Remember that the RPF interface (in this case Tunnel 12) must never appear in the OIL of a (S,G) entry. In the following output we can effectively see that R1 is sending a PIM prune*:
*Note actually that PIM hasn′t a specific PIM prune or PIM join message. There is only a single PIM Join/Prune: message type. Each PIM join/prune message contains both a join list and a prune list. So a router can include multiple entries in the join list or prune list and therefore effectively join/prune multiple sources and/or groups with a single PIM join/prune message.
As our last step let′s make the receiver join the multicast group 239.10.10.10 while the source hasn′t started to forward traffic to this group yet. So if we look at the multicast routing table of R1 we can see the following while the receiver is joining the group:
So R1 is receiving an unsolicited Memb ership report (“join”) for the multicast group 239.10.10.10. This membership report was multicast to 239.10.10.10 from the receiver (20.20.20.2) as the result of joining the multicast group 239.10.10.10. So now R1 has an (*,G) entry for the multicast group 239.10.10.10 in its multicast routing table. The creation of this entry was triggered by the IGMP membership report sent by the receiver:
As we are using Dense mode the incoming entry equal to NULL has no significance here. In Dense Mode only (S,G) entries are used to forward multicast traffic and they build their OIL from the parent (*,G) entry applying the rule saying that the RPF interface must not be present in the OIL of the (S,G) entry. Unlike Sparse Mode R1 will not send a PIM join message because Dense mode is based on the “Implicit join model” which means that all routers in the
multicast domain don′t have an (*;G) entry for 239.10.10.10 considering that the source hasn′t started to send traffic yet.
Please note that every 125 seconds R1 will send an IGMP general query out interface F0/1 (where the receiver is connected) to the multicast address 224.0.0.1 (all hosts multicast group) to find out if any host is interested in receiving packets for any multicast group. After sending the Query R1 expect the receiver to reply with an IGMP solicited membership report for the multicast group 239.10.10.10.
Let′s send some multicast traffic from the source now and see the result on R1 multicast routing table:
So upon receiving the first multicast packet from the source R1 creates an (S,G) entry with the OIL based on its parent entry for this group.
If the receiver were to leave the multicast group it will send an IGMP leave (type 0X17) to all routers Multicast group 224.0.0.2 which will trigger R1 to send an IGMP group specific query to 239.10.10.10 (in our example) in order to check if there are still members that wants to get the multicast stream for this group. If R1 doesn′t get an IGMP membership report from the receiver which is the case in our example as the receiver leaves the multicast group is will set the interface where the receiver is connected in its (S,G) OIL to NULL which will trigger R1 to send a PIM prune to R2 via the tunnel interface. Let′s see the debug output on R1 when the receiver leave the multicast group:
So that is it! Basic multicast PIM Dense Mode has been covered. In my next post I will talk about PIM Sparse mode using the same diagram that I have used in this post. Thanks for reading and your comments are more than welcome.
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What subject(s) are you studying Why did you choose to study that subject Do you like your subject (Why/Why not) Is it very interesting (Possibly) Are you looking forward to working Do you prefer to study in the mornings or in the afternoon Do you have a favorite teacher Do you want to be a teacher in the future What kinds of teachers do you like Do you think teachers should be angry at students or not Do you like strict teachers What's the different between young and old teachers Is it important for teachers to interact with students frequently What ' s the most important part in your study, teachers or classmates What ' s (the name of) your hometown (again) Is that a big city or a small place Please describe your hometown a little. How long have you been living there Do you like your hometown (Possibly) Do you like living there * What do you like (most) about your hometown Is there anything you dislike about it Do you think you will continue living there for a long time What kind of housing/accommodation do you live in Do you live in a house or a flat Who do you live with How long have you lived there Do you plan to live there for a long time (If you answer you haven't lived there long) What's the difference between where you are living now and where you have lived in the past Can you describe the place where you live Which room does your family spend most of the time in What do you usually do in your house/flat/room Are the transport facilities to your home very good Do you prefer living in a house or a flat Please describe the room you live in. What part of your hometown do you like the most 个人信息类 Studies 2. 3. 4. 5. 6. Teachers 1. 2. 3. 4. 5. 6. 7. 8. Hometown 1. 2. 3. 4. 5. 6. 7. 8. 9. Accommodation 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13.
Part1: https://www.doczj.com/doc/494650258.html, ●What is your full name? ●How should i address you? ●Have you got any English name? ●Are there any special meanings about your name? ●Who gave you this name? 2.Studies or work ●Which school are you studying now? what is your major? ●Who choose the major for you before you entering your university? ●What are the advantages and disadvantages of your university? ●Which subject you like most and which subject do you dislike most? Why? ●Do you like the school you are studying at? 3.Home ●Do you live in a house or a flat? ●Please describe the place where you live. ●How have you decorated your home (or, your room)? ●Is there anything (hanging) on the walls of your home (or your room)? (e.g., decorations) ●What can you see when you look out the window of your room (or, the windows of your home)? 4.Hometown ●Where is your hometown? (Or, what part of China do you come from?) ●Do you think you'll always live there? ●Where do you live at the moment? ●Do you like your hometown? (Why?/Why not?) ●What sorts of buildings are there in your hometown? 5.Books & Reading ●Do you like reading (books)? (Why?/Why not?) C ●What (kinds of ) books do you like to read? C ●(Similar to above) What (kinds of ) books do read (for enjoyment)? ●Are you reading any books at the moment? N ●Did you read much when you were a child? 6.Newspapers & Magazines ●What kind of newspaper do you have in China? ●What is your favorite magazine? ●When did you begin to read newspaper? ●What’s the difference between Chinese newspapers? ●Which one do you prefer to read, newspaper or magazine?
Confirmation Questions Good morning/afternoon. How are you? Morning/afternoon. Fine, thank！ How do you do? How do you do? Hi, good to meet you. Good to meet you too. Hi, how are you doing? Not too bad. And you? 1.Can I see your ID card please? Sure, here you are. 2.Could you tell me your full name please? My full name is ……. But you can call me…. 3. And what shall I call you? Mo st people call me …... Hometown Questions 4. Whereabouts is your hometown? Xian is located in Shanxi province, which is in central China. 5. Let's talk about your hometown or village. What kind of place is it? My hometown is a small place, just outside of Beijing. It takes about an hour to reach/get to there. The people there are mostly farmers, but a lot of the young people work in Beijing. It's a quiet place and I like it. 6. Could you tell me something about your hometown? a. Well, it's quite big and it's the capital of Shanxi province. The population's about 6 million and it's famous for its historic sites, especially for the Terracotta Warriors. Xi' an used to be the capital of China, and it's the beginning of the famous Silk Road. b. Okay. Well, my hometown is Beijing and I live just outside of it near the 4th ring road. As you probably know, Beijing's the political and cultural center of China, and it's quite a historical place as well. It's huge-about 12 or 13 million people live in it now-and it seems to be getting bigger every year. 7. What kind of landscape surrounds your hometown? a. Harbin's right near the Song Hua Jiang River and it's kind of in a flat area, with mountains in the distance. b. Indio's a coastal city near the sea, so the main landscapes are the beaches and bays. There are also some nice hills nearby. 8. What are the main tourist attractions in your hometown? There's the Great Wall and the Forbidden City. These are the two that are most well known. They are also symbols of China. They attract most visitors, but there are quite a lot of other famous sites as well. 9. What are the people like in your hometown? They're usually very friendly, but a bit conservative. People still hold onto a lot of old customs and traditions, which is what I mean by conservative. But I think people there are very hospitable and kind. If you ask someone for directions, they'll always try to help you out, or find someone else who can. 10. What places in your hometown do you like best and tell me why? I like the Temple of Heaven best because it's very beautiful. It has a lot of space and there are lots of really nice and old trees there. In the early morning, it's very peaceful.
雅思口语Part1答案：Hometown家乡 1. Where do you come from? Well, I’m from HanDan, an inland city that is in the middle of China. It’s well known for its historical architecture. Also, many travellers like the traditional spicy food, which is a “must-eat” for visitors once they come to town. 我来自邯郸，是个中国中部的内陆城市。邯郸以历史建筑而闻名。而且，很多游客都喜欢邯郸传统的辣食，这是游客们一到邯郸必吃的东西。 2. What tourist attractions are there in your hometown? Actually, there’re several must-see spots here, like the national museums, international shopping malls and other historical heritages. Well, I’d like to mention a place called Sai Kung, which is a famous fishing village. What’s more, there’re many roadside vendors selling different kinds of trinkets along the sea front. 其实，这有很多必看的景点，比如国家博物馆，国际购物中心和其他历史遗产。我要提一下有个叫西贡的地方，是个有名的渔村。海岸前面有很多路边商贩卖各种小玩意儿。
第一节考试第一阶段话题总结 第一阶段主要是关于个人情况的介绍，考官会问一些具体的问题，内容涉及考生的工作、学习情况，家乡，爱好，以及关于身边的衣食住行等问题。 About yourself 1.What’s your full name 2.What’s your English name 3.Does your Chinese name have any special meaning Literally:Lean on a sailing boat to see in the distance Make a good wish that Everything is going smoothly 4.Do you want to change your name Smoothly & successfully Hometown and cities 1.Where do you come from / Where are you from / Where is your hometown Wuhan, a large-sized city in the middle of china, and it is also a crucial city during revolution period in the history
2.Do you think your hometown is a good place for young people to live in 3 aspects: @.local delicious food snack street : hot dry noodles , fried bread stick ,stinky tofu shrimp balls ,spicy hot noodles, hot hot hot, hot pot, spring rolls @shopping malls & amusement parks 国广&欢乐谷 @university city, district relatively high education standard 3.What aspects do you like best in your hometown 4.What aspects do you dislike in your hometown Larged-sized city large population crowded in the station competetion is fierce In the process of contruction of infrustracture ==road traffic jam
雅思part1口语题库大全 雅思口语题库2020【1】 题目： 1.Do you think your city is clean or not? 2.How do you feel when you see people throwing garbage on the street? 3. Why do some people throw garbage on the street? 4.What do you do with garbage when you are on the street? 范文： 1.Do you think your city is clean or not? Well, I suppose my city is quite clean for most of the time, thanks to the hard work of sanitation workers，you can see neat streets and classification trash bins everywhere. By the way, if you travel to my city and take a look, you will be amazed by how perfectly it is maintained as a clean place to live in. 2.How do you feel when you see people throwing garbage on the street? When witnessing people throwing garbage on the street, I always feel very angry, because I think as citizens we all have the responsibility to take care of the city and abide by the regulations. Only by doing this can we build a beautiful and clean home. 3. Why do some people throw garbage on the street? From my understanding, I think people throw garbage on the street mainly because they find it is a more convenient way to get rid of the garbage than throwing it in the garbage bin. Also, I would say it is because there are not enough garbage bins around the city. 4.What do you do with garbage when you are on the street? When I am on the street, first of all I myself would never throw garbage randomly, and would always help keep the street clean. Secondly, if I pass by a piece of garbage on the street, I usually volunteer to pick it up and throw it into the nearest garbage bin. 1-4月雅思口语话题 雅思口语题库2020【2】 题目： 1.Is there a good place to look at the sky where you live?
雅思口语Part1重要性及备考方法 当大家谈论到雅思口语Part1的第一感觉是什么?是不是感觉非常简单。很多同学就是因为感觉Part1太过简单而疏于备考，结果在口语考试中吃了亏。下面就和大家分享实例分析雅思口语Part1重要性及备考方法解析，来欣赏一下吧。 雅思口语Part1重要性及备考方法解析 一. 雅思口语Part1重要性分析 雅思口语Part1既是考试，也是热场环节，这时候如果你表现的非常自信，而且问题也答得很好，就能给口语考官留下好的印象，也能为口语高分奠定基础。相反，如果你因为紧张或者缺乏准备，导致回答时磕磕巴巴，那可能就已经为口语低分“奠定了基础”。所以Part1的表现是会影响雅思口语整体评分的。 二. 雅思口语Part1备考攻略 1. 熟悉各类考试话题 雅思口语考试备考过程中，大家都会用到口语题库。除了受变题季影响，口语题库会有大的变动外，其他时间段内口语题库基本稳定。所以备考雅思口语Part1的时候一定要利用好口语题库，熟悉各类口语话题类型，并且多做练习。大部分情况下，Part1
都是问名字、天气之类的，比如“Does your name have any special meaning? ”，然后你根据自己的名字去说一下寓意即可。但是也有可能会遇到一些平时不常见的话题，比如遇到“Punctuality”的话题时，可能会问你“Do you think it is important to be punctual?”，有的同学可能对“punctual”这个单词还很陌生，遇到这样的话题可能直接就懵了，大脑一片空白。所以熟悉各类口语话题非常重要，不仅可以准备常考话题，也能准备到一些不常见的话题类型。 2. 根据话题准备语料 除了要熟悉各类话题外，还要准备一些语料。不然自己的答案可能会杂乱无章，我们还以上文中的问题为例，当问到你名字的特殊含义时，如果你没有准备过类似的语料，即便你了解自己名字的中文意义，却找不到对应的英文词将其表达出来，可能也会一时语塞，不知如何作答。所以即便是比较简单的Part1部分，我们要准备一些答题的语料，不论问到什么问题，都能侃侃而谈。 3. 切忌背范文 大家在备考的过程中也会发现，虽然Part1比较简单，但是网上也能找到很多模板和范文。有的同学在备考时看到范文就将其背会，以期待在考试中能用上。首先，雅思口语Part1问题类型多变，并不是针对每个话题都有固定问法，所以背范文作用不大;其次，背范文直接在考试中应用如果被发现可能会有作弊嫌疑，所以建议大家不要背记Part1范文，多看多学习即可。